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Cod fishes (Gadidae).

Authors:

Abstract

The atlas presents a unique set of abundance data to describe the spatial, depth, size, and temporal distribution of demersal and pelagic fish species over an extensive marine area, together with accounts of their biology. A large number of pictures, graphs and distribution maps illustrate the text. By largely avoiding - or at least explaining - scientific terms and providing extensive references, the book should be useful for both laymen and scientists. The quantitative information on some 200 fish taxa is derived from 72,000 stations fished by research vessels during the period 1977-2013. The area covers the northwest European shelf from the west of Ireland to the central Baltic Sea and from Brittany to the Shetlands.
1
Order Gadiformes
The Gadiformes represent a large group of species that, with few exceptions, are distributed in the
northern hemisphere. Several have been well studied, because they constitute a major resource for
many fisheries in the North Atlantic. The systematics of the Gadiformes is far from resolved, and
different studies suggest varying hierarchies of families and sub-families (Nelson, 2006; Roa-Varón
and Ortí, 2009). Whilst we treat the Lotinae, Gadinae and Phycinae as sub-families within the
Gadidae, it is recognised that other authors consider these as families in their own right (Lotidae,
Phycidae and Gadidae). Some studies even differentiate the rocklings further, by treating them as
either a distinct family (Gaidropsaridae) or sub-family (Gaidropsarinae).
The species reported represent five families: Macrouridae, Moridae, Gadidae (with the subfamilies
Gadinae, Lotinae, and Phycinae), Merlucciidae and Melanonidae.
Six species of Moridae or deepsea cods and one species belonging to the Melanonidae or pelagic
cods were reported in the surveys, but only from stations >200 m (see Table ###). These are not
further discussed. Three other families (Muraenolepididae or eel cods; Bregmacerotidae or codlets;
Euclichthyidae or eucla cod) are only found in the southern hemisphere or in (sub-)tropical waters.
30. Grenadiers (Macrouridae)
Odd Aksel Bergstad
Family Macrouridae
The Macrouridae, grenadiers or rat-tails, live in deep water along the continental slopes. Altogether 27
genera and about 350 species are known. Of the 16 species occurring in the Northeast Atlantic, only
three have been recorded from stations <200 m roundnose grenadier Coryphaenoides rupestris,
hollowsnout grenadier Coelorinchus caelorinchus
1
, and softhead grenadier Malacocephalus laevis ,
while four more were caught at deeper stations (Table ###). In deeper areas immediately adjacent to
the Atlas area, macrourid diversity is much greater. The northernmost deeper parts of the North Sea
and the slope off Norway are inhabited by the sub-Arctic species Macrourus berglax (Bergstad et al.,
1999), and at least 17 species have been recorded on the continental slope and rise in the North
Atlantic to the west of the British Isles (Haedrich and Merrett, 1988; Priede et al., 2010).
Macrourids have a large head, a short trunk, and a long, tapering and scrubby tail (hence the name
rat-tails) with an inconspicuous caudal fin. Some species have a barbel. The first dorsal fin is short, the
second dorsal fin is long, extending to the end of the body and comprising of short fin rays. The long
anal fin extends from the vent to the tail.
Because of their long, tapering tails that are easily damaged, measuring grenadiers in a consistent
way presents difficulties and over the years, essentially two types of measurements have been applied
(see Box on p. ###). However, the method was not always specified and therefore arbitrary decisions
had to be taken to be able to combine all information into one set of length measurements (LT).
Nevertheless, the LFDs shown for the three species should provide a reasonable approximation of the
total length distributions over the whole area.
Because only a minor fraction of the distribution area of these deep-water species has been surveyed,
the data collected do not provide reliable information on abundance trends in any of these stocks.
1
The spelling of the scientific name has been confusing! We stick to WoRMS.
2
30.1 Roundnose grenadier Coryphaenoides rupestris
Gunnerus, 1765
DE: Rundnasengrenadier ;ES: Granadero de roca ;FR:
Grenadier à nez rond ;NL: Grenadier ;NO: Skolest
Lmax: 150 cm LT (Geistdoerfer, 1986)
Data range: size 5117 cm; depth 41763 m
Presence/absence of roundnose grenadier.
General
Roundnose, or rock grenadier, is the largest, most common, and best studied species of the three.
Taxonomy and identification: C. rupestris have a rounded head and a blunt snout with an almost
terminal mouth. The second finray in the first dorsal fin has a serrated front edge. The scales are large
and deciduous. For more details on identification, a specialist key has to be used (Geistdoerfer, 1986).
Biogeographical distribution: All three species have a distribution extending far beyond the survey
area. C. rupestris ranges from the Bay of Biscay northward at least to Vestfjorden (including deeper
shelf troughs and fjords) in north Norway (Eliassen, 1983). It is also found on the Mid-Atlantic Ridge
from Iceland to the Azores and in the Northwest Atlantic from slopes off Greenland south to Bermuda
(Haedrich and Merrett, 1988).
Survey data
Spatial distribution: The roundnose grenadier was reported in large numbers from the Norwegian
Deeps and Skagerrak, and much less so from the slope to the west of Britain, with a few records from
the central northern North Sea.
Depth distribution: The Atlas data originate from surveys that only sample the shallower parts of the
depth range of macrourids and are obviously not well suited for delineating the distribution of
grenadiers by depth zone. The data suggest that roundnose grenadiers favour the deeper shelf areas
(>400 m). This is largely in agreement with the available information on depth distribution of this
species: upper, middle and lower slope at 2502000 m depth (Bergstad, 1990; Geistdoerfer, 1986;
Haedrich and Merrett, 1988; Priede et al., 2010).
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59
60
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Coryphaenoides rupestris
3
Overall depth (left) and length (right) distribution.
Size distribution: The LFD of roundnose grenadier is relatively broad, but few individuals exceeded
100 cm. The maximum reported size was 117 cm, well below the Lmax of 150 cm.
Time series: Catches of roundnose grenadier have been irregular in both ecoregions. A recent history
of the size distributions of roundnose grenadier in the Skagerrak, including the data from the
Norwegian Pandalus survey, indicates large shifts over the period 19842013 in response to
exploitation and recruitment variability (Bergstad et al., 2013).
Survey indices by ecoregion.
Biology
Habitat: Grenadiers are typically deep-water species living on the continental slopes and the deep
ocean floor, the abyssal plain.
Age, growth and maturity (for growth parameters see Table ###): Among the three species, roundnose
grenadier is the only one that has been studied extensively by counting growth zones in otoliths
(Bergstad, 1990; Kelly et al., 1997; Gordon and Swan, 1996). Growth is generally slow and estimates
of the longevity are in the order of at least 6070 years. Females grow larger than males, and
maximum size is somewhat higher in the western subareas compared with the Skagerrak. Maturity
ogives in the two areas are similar (Bergstad, 1990; Kelly et al., 1997; Allain, 2001; Lorance et al.,
2001, 2008), indicating that A50% is about 8 (males) or 10 years (females), corresponding to an L50% of
8 and 11 cm Lpaf, respectively.
Reproduction: Roundnose grenadiers spawn in the Skagerrak in late autumn (Bergstad and Gordon,
1994), and on the upper slope to the west of the British Isles for a more protracted period (Allain,
2001). There is no indication of specific spawning areas. They are batch spawners with a fecundity of
470 thousand oocytes per batch, but annual fecundity could not be determined (Allain, 2001).
Early stages: Eggs of some species have been well described (Merrett, 1978, 1986), but only
scattered data are available on their occurrence in various parts of their distribution ranges. All three
species have pelagic eggs, larvae and early juveniles (Merrett, 1986). Embryos appear very primitive
at hatching. Although older information suggested that roundnose grenadier eggs ascend to the
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
Coryphaenoides
rupestris
0.0
0.5
1.0
0 25 50 75 100
length class (5 cm)
Coryphaenoides
rupestris
Y
0
2
4
6
8
1977 1982 1987 1992 1997 2002 2007 2012
Coryphaenoides rupestris
0
2
4
6
8
1977 1982 1987 1992 1997 2002 2007 2012
Coryphaenoides rupestris
4
surface and that larvae gradually descend to meso-pelagic depths (Merrett, 1978), eggs and larvae
have in the Skagerrak only been found during winter/spring at depths >150 m and their absence in
extensive egg and larval collections from near-surface waters makes shallower occurrence unlikely
(Bergstad and Gordon, 1994). The duration of the different life phases is not well known, but the truly
pelagic period is at least 6 months, because juveniles are first caught on the bottom in early autumn.
At that time, they tend to be restricted to the deepest trough of 500700 m (Bergstad, 1990; Bergstad
and Gordon, 1994). In the Rockall Trough and Porcupine Bank area, small fish appear to be most
abundant at intermediate depths but more or less absent from the shallowest and deepest parts
(Mauchline and Gordon, 1984; Lorance et al., 2008).
Movements and migrations: The substantial concentrations of roundnose grenadier in midwater
(several hundreds of metres above the seafloor) observed by hydroacoustics and midwater trawl
sampling suggest temporal excursions off the bottom (Bergstad, 1990).
Trophic ecology: Juvenile roundnose grenadier maintain a pelagic diet comprising of small pelagic and
suprabenthic copepods, ostracods, mysids, euphausiids, amphipods and decapods, while larger
individuals may also prey on cephalopods and small fish (Mauchline and Gordon, 1984; Mauchline et
al., 1994; Bergstad et al., 2003).
Stock structure: According to a recent trans-Atlantic molecular-genetic study, roundnose grenadier
from the Skagerrak and a coastal trough off mid-Norway had a substantially different genetic identity
from conspecifics sampled at truly Atlantic locations. Although some heterogeneity existed among the
more oceanic sites, differences were much smaller than between the North Sea and all other sites.
This suggests that the Skagerrak and other troughs and fjords around Norway may host an isolated
population, and that connectivity between populations at distant locations within the North Atlantic is
also rather limited (Knutsen et al., 2012).
Exploitation
Roundnose grenadier has been exploited in a directed fishery that was initiated by the former USSR in
the Northwest Atlantic in the late 1960s, using bottom or bentho-pelagic trawls. This fishery moved
across the Mid-Atlantic Ridge to the European slope (Troyanovsky and Lisovsky, 1995; Shibanov and
Vinnichenko, 2008), where it developed into an international fishery that expanded further in the mid-
1980s. Although assessments are uncertain, biomass may have declined to 50% (or perhaps 20%) of
the virgin biomass (Lorance et al., 2008; Bailey et al., 2009). In the Skagerrak, roundnose grenadier
has been a bycatch in the bottom-trawl fishery for shrimp for a long time, but became the target of a
small-scale fishery in the 1980s (Bergstad, 1990; Bergstad et al., 2013). The annual landings were
usually around 3000 t or less but increased rapidly in 20032005 to an unprecedented 1012
thousand t. This harvesting level was considered unsustainable, and the fishery has been closed in
2006 as a precautionary measure to avoid stock depletion (Hansen et al., 2011).
5
30.2 Hollowsnout grenadier Coelorinchus
caelorinchus (Risso, 1810)
DE: Schwarzfleckgrenadier; ES: Granadero
tristón; FR: Grenadier raton; NL: Kleine
grenadier; NO: Spiritist
Lmax: 38 cm LT (Geistdoerfer, 1986)
Data range: size 238 cm; depth 180763 m
Presence/absence of hollowsnout grenadier.
Summary
C. caelorinchus, the smallest of the three species, are characterised by their sharply pointed snout.
The head has a prominent bony ridge extending back below the eye. The second finray in the first
dorsal fin is a smooth flexible spine. The vent is close to the origin of the anal fin. Hollowsnout
grenadier occur rarely northeast of the Wyville-Thomson Ridge, but are distributed much further south
along the European-African slope (Haedrich and Merrett, 1988), and also occur in the Mediterranean
Sea (Geistdoerfer, 1986). In the Porcupine Bank area, hollowsnout grenadier was more abundant than
the other two grenadier species. More scattered records came from Rockall and along the 200 m
isobath into the Norwegian Deeps. They were most abundant in waters of 300500 m depth. The
depth distribution indicated in the literature is the upper and middle continental slope at 1401300 m
(Geistdoerfer, 1986; Haedrich and Merrett, 1988; Priede et al., 2010).
Overall depth (left) and length (right) distribution.
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50
51
52
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54
55
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59
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61
62
Coelorinchus caelorinchus
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
Coelorinchus
caelorhincus
0.0
0.5
1.0
0 6 12 18 24 30 36
length class (2 cm)
Caelorinchus
caelorhincus
6
Survey indices in the CSER.
The LFD shows two peaks at 614 and 1629 cm. The estimated size of the largest fish equalled the
reported Lmax of 38 cm. Hollowsnout grenadier appear to be strongly increasing during recent years.
The food consists primarily of benthic invertebrates (polychaete worms, squat lobsters and
gastropods), but suprabenthic prey, such as amphipods, copepods, mysids, euphausiids, isopods and
natantid shrimps, are also taken (Mauchline and Gordon, 1984; Geistdoerfer, 1986).
0
1
2
3
4
5
6
1977 1982 1987 1992 1997 2002 2007 2012
Coelorinchus caelorhincus
7
30.3 Softhead grenadier Malacocephalus
laevis (Lowe, 1843)
DE: ; ES: Abámbolo de bajura ; FR:
Grenadier barbu ; NL: ; NO: Småskjellet
skolest
Lmax: 50 cm LT (Geistdoerfer, 1986)
Data range: size 355 cm; depth 180763 m
Presence/absence of softhead grenadier.
Summary
M. laevis have a short and blunt snout, large eyes, and large jaws with curved teeth. The second finray
in the first dorsal fin is smooth. Its scales are small. The vent is closer to the anal fin than to the pelvic
fins. It occurs rarely northeast of the Wyville-Thomson Ridge, but is distributed much further south
along the European-African slope (Haedrich and Merrett, 1988). In the surveys the species was
reported in lower numbers in the Porcupine Bank area, but more frequently around the 200 m isobath
west of the British Isles than the two others. May also be found at Rockall. Its typical habitat, the upper
slope at 200700 m, is is at somewhat shallower depths than the other two species (Geistdoerfer,
1986; Haedrich and Merrett, 1988; Priede et al., 2010).
Overall depth (left) and length (length) distribution
-14 -12 -10 -8 -6 -4 -2 0246810 12 14 16 18 20 22 24
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58
59
60
61
62
Malacocephalus laevis
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
Malacocephalus
laevis
0.0
0.5
1.0
0 10 20 30 40 50
length class (2 cm)
Malacocephalus
laevis
8
Survey indices in the CSER
Although the Lmax of 50 cm was exceeded by 5 cm, these lengths represent converted values from Lpaf
measurements and should not be taken for granted. The LFD shows a high and narrow peak at 1820
cm and a small one of juvenile fish at 68 cm. In the CSER, softhead grenadier has been most
abundant in the 1990s and seems to be increasing again recently. The diet comprises epibenthic
animals, specifically squat lobsters (Mauchline and Gordon, 1984).
References
Allain, V. 2001. Reproductive strategies of three deep-water benthopelagic fishes from the northeast Atlantic
Ocean. Fisheries Research, 51: 165176.
Bailey, D. M., Collins M. A., Gordon J. D. M., Zuur, A. F., and Priede I. G. 2009. Long-term changes in deep-water
fish populations in the North East Atlantic: deeper-reaching effect of fisheries? Proceedings of the Royal
Society, B., 275: 19651969.
Bergstad, O. A. 1990. Distribution, population structure, growth and reproduction of the roundnose grenadier
Coryphaenoides rupestris (Pisces:Macrouridae) in the deep waters of the Skagerrak. Marine Biology, 107:
2539.
Bergstad, O. A., Bjelland, O., and Gordon, J. D. M. 1999. Fish communities on the slope of the eastern
Norwegian Sea. Sarsia, 84: 6778.
Bergstad, O. A., and Gordon, J. D. M. 1994. Deep-water ichthyoplankton of the Skagerrak with special reference
to Coryphaenoides rupestris Gunnerus, 1765 (Pisces: Macrouridae) and Argentina silus (Ascanius,
1775)(Pisces, Argentinidae). Sarsia, 79: 3343.
Bergstad, O. A., Øverbø Hansen, H., and Jørgensen, T. 2013. Intermittent recruitment and exploitation pulse
underlying temporal variability in a demersal deep-water fish population. ICES Journal of Marine Science,
doi:10.1093/icesjms/fst202.
Bergstad, O. A., Wik, Å. D., and Hildre, Ø. 2003. Predator-prey relationships and food sources of the Skagerrak
deep-water fish assemblage. Journal of Northwest Atlantic Fisheries Science, 31: 165180.
Eliassen, J. E. 1983. Distribution and abundance of roundnose grenadier (Coryphaenoides rupestris Gunnerus)
(Gadiformes, Macrouridae) in northern and mid-Norway. ICES Document CM 1983/ G:43. 24 pp.
Geistdoerfer, P. 1986. Macroruridae. In Fishes of the North-eastern Atlantic and the Mediterranean. Volume II, pp.
644676. Ed. by P. J. P. Whitehead et al. UNESCO, Paris. pp. 5171007.
Gordon, J. D. M., and Swan, S. C. 1996. Validation of age readings from otoliths of juvenile roundnose grenadier,
Coryphaenoides rupestris, a deepwater macrourid fish. Journal of Fish Biology, 49 (Suppl. A): 289297.
Haedrich, R. L., and Merrett, N. R. 1988. Summary atlas of deep-living fishes in the North Atlantic. Journal of
Natural History, 22: 13251362.
Hansen, H. Ø, Bergstad, O. A., and Jørgensen, T. 2011. Update on Norwegian fishery independent information
on roundnose grenadier (Coryphaenoides rupestris) in the Skagerrak and north-eastern North Sea (ICES
Division IIIa and IVa). Working Document, ICES WGDEEP, February 2011, 16p.
Kelly, C. J., Connolly, P. L., and Bracken, J. J. 1997. Age estimation, growth., maturity and distribution of the
roundnose grenadier from the Rockall Trough. Journal of Fish Biology, 50: 117.
Knutsen, H., Jorde, P.E., Bergstad, O.A., and Skogen, M. 2012. Population genetic structure in a deepwater fish
Coryphaenoides rupestris: patterns and processes. Marine Ecology Progress Series, 460: 233246.
Lorance P., Bergstad O. A., Large P. A., and Gordon J. D. M. 2008. Grenadiers in the North East Atlantic
distribution, biology, fisheries and their impacts, and developments in stock assessment and management.
American Fisheries Society Symposium, 63: 365397.
Lorance, P., Dupouy, H., and Allain, V. 2001. Assessment of the roundnose grenadier (Coryphaenoides rupestris)
stock in the Rockall Trough and neighbouring areas (ICES Sub-areas VVII). Fisheries Research, 51:151
163.
Mauchline, J., and Gordon, J. D. M. 1984. Diets and bathymetric distributions of the macrourid fish of the Rockall
trough, northeastern Atlantic Ocean. Marine Biology, 81: 107121.
0
1
2
3
4
5
6
1977 1982 1987 1992 1997 2002 2007 2012
Malacocephalus laevis
9
Mauchline, J., Bergstad, O. A., Gordon, J. D. M., and Brattegard, T. 1994. The food of juvenile Coryphaenoides
rupestris Gunnerus, 1765 (Pisces, Macrouridae) in the Skagerrak. Sarsia, 79: 163164.
Merrett, N. R. 1978. On the identity and pelagic occurrence of larval and juvenile stages of rattail fishes (Family
Macrouridae) from 60o N, 20o W and 53o N, 20o W. Deep-Sea Research, 25: 147160.
Merrett, N. R. 1986. Macrouridae of the Eastern North Atlantic. Fiches d’Identification du Plancton, No. 173–175.
14p., ICES, Copenhagen.
Priede, I. G., Godbold, J. A., King, N. J., Collins, M.A., Bailey, D.M., et al. 2010. Deep-sea demersal fish species
richness in the Porcupine Seabight, NE Atlantic Ocean: global and regional patterns. Marine Ecology, 31:
247260.
Roa-Varón, A., and Ortí, G. 2009. Phylogenetic relationships among families of Gadiformes (Teleostei,
Paracanthopterygii) based on nuclear and mitochondrial data. Molecular phylogenetics and evolution, 52:
688704.
Shibanov, V. N., and Vinnichenko, V. I. 2008. Russian investigations and the fishery of roundnose grenadier in
the North Atlantic. American Fisheries Society Symposium, 63:399412.
Troyanovsky, F. M., and Lisovsky, S. F. 1995. Russian (USSR) fisheries research in deep waters (below 500 m)
in the North Atlantic. In Deep-water fisheries of the North-Atlantic Oceanic Slope. pp. 357366. Ed. by A. G.
Hopper. NATO ASI Series, Series E. Applied Sciences, vol. 296. 420p.
Generic references
Nelson, J. S. 2006. Fishes of the world. Fourth edition. John Wiley & Sons, Hoboken, New Jersey. 601 pp.
10
BOX Measuring, reporting, and processing size information
From http://en.wikipedia.org/wiki/Fish_measurement
There are various ways to measure fish length (Figure X). The common procedure in fisheries
research is to measure total length (LT) by folding the tail fin and record on a measuring board with cm
divisions in which cell it ends (‘measurement to the cm below’). Measurements of standard length (LS),
the distance between the nose or jaw (whichever protrudes) and the end of the body (disregarding the
tail), require more handling time, because the tail hides the scale partitioning on the measurement
board. Therefore, LS measurements are largely reserved for taxonomists who measure only a few fish
in a laboratory rather than thousands on board of a rolling vessel before the next catch comes in.
Presumably, ‘real scientists’ in white coats would also round to the nearest cm (or even in mm), which
might cause a small discrepancy in translating LT into LS (or vice versa), but species-specific
knowledge of the average relative tail length would be needed anyhow. Luckily, this is a non-problem
when dealing only with survey data, although comparisons of the data collected with the ‘scientific
literature’ may be problematic.
[Include here a photograph of a fish measuring board with a heap of fish]
Most fish are measured in cm, but some species such as herring and sprat are routinely measured in
half cm, because their investigators consider them to be a special case. Some species may be even
measured to the mm below. But whichever unit is chosen, fish length will go down in the records to the
length class below, i.e. if you are a fish with an actual size of 127.8 mm, you may be recorded as
being 12 cm if you were a cod, 12.5 if you were a herring, and 127 mm, if you were a salmon or an
anchovy. For instance, the recorded size depends on how hard you press the fish against the wall that
marks the beginning of the graduated ruler. Sport fishers champions would know how to cheat: take a
large cod by the tail, give it a jerk, and suddenly it could have become 5 cm longer!
So far, so good for a data analyst, because all these measurement units can be brought under a
common enumeration of being measured to the cm below, i.e. 12 cm. At least, when the measurement
unit is coded correctly (the standard being ‘1’ for cm classes, ‘0’ for half cm, and ‘.’ for mm).
Regretfully, this is not always the case. In DATRAS, the ICES database for survey data, anchovies
have been reported in the range of 97156 cm (length-code ‘1’). So some error must be involved
somewhere. There are two options: the data could be rejected altogether (with the inherent danger
that we underestimate the abundance of anchovy and biodiversity), or a sensible correction could be
made, which in this case would be that the anchovies have been recorded in mm rather than cm.
Wherever possible, we have chosen the common-sense option.
[Include here a photograph of a punch card, a sorting machine, and an electronic measuring board]
In the old days, fish measurements involved two people, one with dirty hands measuring the fish and
one with clean hands who tallied the scores on sheets with preprinted size partitions. Subsequently,
endless piles of sheets had to be processed at the laboratory by means of old-fashioned calculating
machines. Later on the punch card was invented: the tally sheets had to be translated into paper fish
11
with holes in it that represented all kind of information, length, weight, sex etc., each card representing
one paper fish. To avoid punching errors, all data were entered twice by different punching typists,
who had never seen a fish. The entries were then compared for potential mistakes. Correcting was a
tedious process, but the system worked well for typos, not for errors caused by bad readability of the
tally sheets! And later, everything was again transformed into electronic fish that could be processed
by computers only. However, if an odd electronic fish turned up, one could still go back to the original
tally sheets to check whether something had gone wrong along the way. Nowadays, measuring and
recording are often done simultaneously by one person using an electronic measuring board: after
entering a species and a sample code, each fish is put on the board and by running your finger with a
magnet over the scale partition, where the tail ends, the recorder is activated. It is all very efficient, but
a check later on is no longer possible. Moreover, with two people sitting at the table, the chances for
noticing an actual mis-identification or a tally error is considerably larger than when everything is in the
hands of a single person. Progress is not always what it seems.
BOX Measuring grenadiers
Grenadiers, as well as other off-shelf species such as rabbitfish, have presented a pressing problem to
their investigators, who want to report on their size, because not only their fins but even their tails
break off easily in the catching process. Therefore, neither LT nor LS can often be measured correctly.
Other size measurements would seem appropriate to ensure consistency among scientific
investigations. This problem applies particularly to grenadiers (although also rabbitfish suffer from the
same characteristics), because their body tapers gradually into a narrow projection so that it is virtually
impossible to see where the body ends and where the tail begins. And because the tail easily breaks
in the catching process, neither LT or LS are very useful parameters. In this case, the pre-anal fin
length (LPAF), i.e. the length of the fish between the tip of the snout and the anus has been advertised
as the appropriate measurement unit and appears to be used frequently on board of various research
vessels nowadays. However, the problem is that it is not apparent, when the data collected refer to LT
and when to LPAF.
To investigate this matter, the length distributions of grenadiers by survey and by year have been
plotted and the results appear to be fairly consistent. This is highlighted in Figure ###, showing
markedly different size compositions within individual surveys among periods. By applying a rough
relationship LT=2*LPAF, these findings can be compared with the overall length distributions given for
the various species. Although the multiplication factor might of course be improved by a special study,
we are of the opinion that the data presented approximate the absolute differences in LFD among
species and areas pretty closely or at least better than the original data.
A conversion equation for differently measured grenadiers is LT= 4.73 LPAF 1.64 (Atkinson, 1981).
12
31. Hakes (Merlucciidae)
Henk J. L. Heessen and Hilario Murua
Family Merluciidae
Within the Merlucciidae or hakes three subfamilies are distinguished, altogether with 5 genera and 22
species. Only one representative, Merluccius merluccius, is found in the Atlas area.
31.1 European hake
Merluccius merluccius
(Linnaeus, 1758)
DE: Seehecht; ES: Merluza
europea; FR: Merlu; NL: Heek;
NO: Lysing
Lmax: 180 cm (Wheeler, 1978)
Data range: size 3130 cm; depth 71105 m
Catch rates of European hake.
General
European hake is a piscivorous, demersal as well as bentho-pelagic gadoid with a large mouth full of
sharp teeth and a ferocious appearance. It is also highly valued, especially in Iberian fisheries and in
the Mediterranean Sea. The information provided here is largely based on a review by Murua (2010),
where more references can be found.
Taxonomy and identification: The genus Merluccius has once been included in the Gadidae, but is
now considered to represent a separate family. The genus Merluccius comprises about 15 species
worldwide, but only one representative occurs in the Atlas area. European hake has no barbel, a
straight lateral line, two dorsal fins and one anal fin. In adults, the pelvic fins do not extend to the anal
opening. The jaws are strong with large teeth and the inside of the mouth is almost black. The dark
grey colour of the back becomes lighter on the sides and the belly is silvery white.
13
Biogeographical distribution: The distribution is restricted to the Northeast Atlantic from north Norway
and Iceland to the Gulf of Guinea, including the Mediterranean and Black Seas. Not at the Azores.
Survey data
Spatial distribution in the Atlas area: Hake is most abundant to the west of the British Isles, in the
northern North Sea, and also in the Skagerrak and Kattegat. The species is hardly found in the
eastern part of the English Channel, the Southern Bight, and absent from all but the most western part
of the Baltic Sea.
Depth distribution: Catch rates in both the CSER and NSER were highest on the outer shelf and the
upper part of the slope, but in the BSER they were caught in shallow waters only.
Depth distribution by ecoregion.
Size distribution: There are marked differences in the LFD among ecoregions. The catches in the
CSER were dominated by small fish (1020 cm), in the BSER by relatively large fish (3040 cm), and
in the NSER by sizes in between (1535 cm). When plotted by depth band, the outer shelf (<200 m)
proves to have relatively more small hake than the slope region (>200 m).
Length distributions: by ecoregion (left), and by depth band (right).
These differences can also be visualised in maps for small (<25 cm) and larger (>25 cm) hake
separately. Small hake are concentrated on the outer shelf southwest of Ireland and to the west of
Scotland, while the larger hake are more homogeneously distributed along the shelf edge of the entire
Atlas area, while they are also penetrating much farther into the Irish Sea, Channel area, North Sea
and even the Baltic Sea.
0.0 0.5 1.0
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Merluccius
merluccius
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merluccius
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merluccius
0.0
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025 50 75 100 125
lfd
length class (5 cm)
Merluccius
merluccius
E
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L
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lfd
length class (5 cm)
Merluccius
merluccius
<200 m
>200 m
14
Catch rates of small (<25 cm; left) and larger (>=25 cm; right) hake.
Time series: Despite large annual fluctuations, the average annual catch rate has clearly increased in
the CSER since the start of the surveys. In the NSER, they have remained stable until the early 2000s,
when catches of hake suddenly rose to an unprecedented level. In the BSER, the indices point to
short-lived influxes in 1996 and in the mid-2000s.
Survey indices by ecoregion.
These trends are of course influenced by variations in survey coverage. However, when the data are
split into three periods (19771989, 19901999, and 20002011), it becomes clear that in all areas
surveyed consistently, European hake have undergone major and positive changes in abundance.
Catch rates of hake by period: 19771989 (left), 19901990 (middle), and 20002011(right).
Biology
Habitat: Hake live close to the bottom during daytime, but move up the water column at dusk and
down at dawn. Adult hake live and spawn along the shelf edge, in places with a rough bottom often
associated with canyons and cliffs, whereas small juveniles occur mainly in outer shelf seas and older
ones penetrating to the inner shelf in some years.
Age, growth and maturity: Ageing from otoliths has been proven difficult and because of this, hake has
in the past been identified either as low-growing or as a fast-growing species. International agreement
on the best method for ages up to 5 years has been only reached by around 2000. Otoliths of older
fish still pose problems. Up to age 3, males grow faster than females, but thereafter females start to
grow faster, whereas growth rates of males decline. This is presumably caused by the onset of
maturity. As in many other species, females reach a larger size, and grow older than males. All big
specimens are female. The maximum age is currently believed to be around 12 years. Based on a
0
1
2
3
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Merluccius merluccius
0
1
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3
4
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Merluccius merluccius
0
2
4
6
8
10
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Merluccius merluccius
15
recent tagging study, hake is definitely quite fast-growing, which has been confirmed by studies of
daily growth increments (Piñeiro et al., 2007, 2008). In the light of these results, the age-reading
protocol is currently being revised. In the Bay of Biscay and in Galician waters, males and females
reach maturity at around 35 cm and between 45 and 50 cm, respectively. Males mature at a younger
age than females.
Reproduction: Spawning activity takes place almost all year round, but the main season lasts from
December to July, being somewhat earlier in the south than in the north. The main spawning areas are
situated beyond the shelf edge off the French coast in the Bay of Biscay, off west Ireland, and a
smaller one off the northwest coast of the Iberian Peninsula. Hake is an indeterminate spawner,
meaning that the number of eggs produced in the forthcoming season is not fixed prior to the onset of
spawning, and therefore cannot be determined beforehand. It is also a batch spawner: eggs are
released in a number of batches during the reproductive season (estimates of the interval between
consecutive batches run from 512 days). Therefore, estimates of the annual egg production can only
be made on the basis of the number of oocytes released per batch (batch fecundity), the percentage
of females spawning per day (spawning fraction), and the duration of the spawning season.
Combining such data has provided estimates of the relative egg production for the Bay of Biscay,
which vary from 985 in January/March to 445 eggs per g gutted female in April/October.
Early stages: The pelagic eggs are concentrated in the upper 200 m of the water column over the shelf
break at an ambient temperature of 1013ºC, which appears to be the optimum for spawning. They
are spherical with a diameter of 0.941.03 mm and contain a single oil globule measuring 0.250.28
mm (Russell, 1976). Early larvae (<8 mm) are present in broadly the same area. Shortly after, they are
displaced coastward towards the main nursery areas over the outer continental shelf. This transport
appears to be a critical factor for later survival. In the Bay of Biscay, larvae settle on the seabed
around 40 days after hatching. The 0-group fish usually live on muddy parts of the continental shelf at
depths ranging from 70 to 200 m, with highest abundances around 100 m. A main nursery area is
situated on the large mud-plain La Grande Vasière along the French coast, and another one on the
shelf off the southwest coast of Ireland.
Movements and migrations: Although clear spawning and nursery areas exist, and adults apparently
disperse after spawning, no specific migration patterns have been reported.
Trophic ecology: Juveniles (<20 cm) mainly feed on decapod prawns and euphausiids. Between 20
and 40 cm, the diet consists of fish (blue whiting, horse mackerel, mackerel and clupeoids). Above 40
cm, food composition varies between areas, depth zones and seasons. Blue whiting represent the
main food in the Cantabrian Sea, anchovies in the Celtic Sea, and horse mackerel may be the main
prey elsewhere. Mackerel, poor cod and bib have also been reported as favoured prey. Cannibalism
may account for 420% in percentage volume.
Stock structure: For management purposes, two stocks are distinguished in the Northeast Atlantic,
with a split at the Cap Breton Canyon (close to the border between French and Spanish waters).
Genetic studies, however, have not revealed any evidence for multiple populations in European
waters.
Exploitation
The large scale exploitation only began during the first half of the twentieth century. Both technological
developments to exploit a deep-water species efficiently (and rigorously) and the collapse of major cod
stocks may have played a role. European hake is nowadays a valuable and heavily exploited species.
EU legal minimum landing size is 27 cm in the Northeast Atlantic and 20 cm in the Mediterranean Sea.
References
16
Murua, H. 2010. The biology and fisheries of European hake, Merluccius merluccius, in the North-East Atlantic.
Advances in Marine Biology, 58: 97154.
Piñeiro, C., Rey, J., de Pontual, H., and Garcia, A., 2008. Growth of Northwest Iberian juvenile hake estimated by
combining sagittal and transversal otolith microstructure analyses. Fisheries Research, 93: 173178.
Piñeiro, C., Rey, J., De Pontual, H., and Goñi, R., 2007. Tag and recapture of European hake (Merluccius
merluccius L.) off the Northwest Iberian Peninsula: First results support fast growth hypothesis. Fisheries
Research, 88: 150154.
Generic references
Russell, F.S. 1976. The eggs and planktonic stages of British marine fishes. Academic Press, London. 524 pp.
Wheeler, A. 1978. Key to the fishes of northern Europe. Frederick Warne, London. 380 pp.
17
32. Cod fishes (Gadidae)
John R.G. Hislop, Odd Aksel Bergstad, Tore Jakobsen, Henrik Sparholt, Tom Blasdale, Peter J.
Wright, Matthias Kloppmann, Nicola Hillgruber, and Henk J. L. Heessen
Family Gadidae (Subfamily Gadinae) Cod fishes
Of all Gadiformes, the Gadidae comprise by far the most numerous species in the surveys, and also
some of the economically most important ones. The subfamily Gadinae may be found in temperate
and cold waters in the Atlantic, the Arctic and the Pacific, mostly on the shelf or off the shelf edge, but
some ranging further offshore pelagically. Sixteen genera and 31 species are known, of which 12
species occur in the Northeast Atlantic (Nelson, 2006). They usually have 2 or 3 dorsal fins, 1 or 2
anal fins, all lacking true spines and many having a chin barbel. Because the scales are mostly small,
their bodies can feel rather soft.
32.1 Silvery pout Gadiculus argenteus Guichenot, 1850
DE: Silberdorsch; ES: Faneca plateada; FR: Gadicule; NL: Zilverkabeljauw; NO: Sølvtorsk
Lmax: 15 cm (Wheeler, 1978)
Data range: size 220 cm; depth 201105 m
Catch rates of silvery pout (size range: 220 cm; depth range: 201105 m).
General
A short-lived, small gadoid found all along the edge of the continental shelf and beyond, straying
sometimes onto the inner shelf. The good thing about silvery pout is that it has no congeners with
which it can be confused. A silvery pout is a silvery pout for everyone.
Taxonomy and identification: Silvery pout represents the monospecific genus Gadiculus. The lower
jaw is projecting beyond the upper jaw (no chin barbel), and the mouth is pointed upwards. The large
eyes have a diameter that exceeds the snout length. Scales are large but deciduous. Sensory canals
on top of the head form deep, open pits (Svetovidov, 1986). Two subspecies have been described: G.
argenteus thori Schmidt, 1914 and G. argenteus argenteus Guichenot, 1850 (for morphometric and
meristic characteristics, see Mercader and Vinyoles, 2008).
18
Biogeographical distribution: Silvery pout is encountered all along the continental shelf, and beyond,
from the North Cape (western Barents Sea) down to northwest Africa and the eastern Mediterranean
Sea, G. argenteus thori and G. argenteus argenteus inhabiting the waters north and south of the Bay
of Biscay, respectively. The boreal distribution of the former includes the northern North Sea and
Skagerrak (Svetovidov, 1986, Wienerroither et al., 2011), but the species appears to be absent from
the Baltic Sea and from the Faroe Islands.
Survey data
Spatial distribution: The species is common in the Skagerrak, northern North Sea, and along the
western seaboard of the British Isles and in the Celtic Sea. Catch rates were particularly high at
Rockall and in the Porcupine Bank area. In the northern North Sea, the distribution coincides almost
perfectly with the 100 m isobath. The overall pattern strongly resembles the distribution of blue whiting
Micromesistius poutassou. Although occurring predominantly on the outer shelf, strayers are
occasionally recorded in low numbers from inner shelf locations.
Depth distribution: In the NSER, catch rates were highest at depths of 150300 m, but fair numbers
have been caught in the 125150 m depth class. In the CSER, the highest abundances were
observed beyond 200 m depth. Although this is in line with reports of a more extensive depth range
down the continental slope (2001000 m; Svetovidov, 1986; Haedrich and Merrett, 1988), few were
actually caught beyond 500 m. The catches reported from relatively shallow waters must refer to
strayers.
Depth distribution by ecoregion.
Size distribution: The LFD is bimodal for the CSER, with peaks at 7 and 12 cm, and unimodal with a
peak at 10 cm for the NSER. These peaks appear to be related to the depth distribution, large
individuals being almost absent in waters <200 m deep. The maximum lengths reported in both the
ecoregions (19 and 20 cm, respectively) exceed the published Lmax of 15 cm (Wheeler, 1987)
considerably.
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Gadiculus
argenteus
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Gadiculus
argenteus
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Gadiculus
argenteus
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7
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lfd
length class (cm)
Gadiculus
argenteus
<200 m
>200 m
19
Length distributions: overall (left), and by depth band (right).
Time series: In the NSER, abundance has varied without a clear trend. In the CSER, abundance in all
surveys was much higher during the last 5 years.
Survey indices by ecoregion.
Biology
Habitat: Silvery pout live in deep water, near the edge of the continental shelf, mainly at depths of
150400 m, where they aggregate over various types of bottom (Cohen et al., 1990).
Age, growth and maturity: Silvery pout rarely becomes older than 3 years based on analyses of mode
shifts in size-distributions. In the northern North Sea, 0-groups appear in bottom-trawl catches in
October and the cohort can be followed during the next winter and spring as a distinctive mode of the
specimens <10 cm (Albert, 1993). Being a short-lived species, maturity is presumably reached by the
majority of the 2-year-old fish, while some may even spawn at age 1.
Reproduction: Spawning takes place in mid-winter and spring (Cohen et al., 1990) and may occur over
much of the distribution area.
Early stages: Eggs and larvae have been described by Ehrenbaum (1909) and Schmidt (1909).
Larvae are pelagic for an unknown period of time, but presumably become bentho-pelagic in the early
summer (Russell, 1976). Bentho-pelagic juveniles are found over the entire distribution range and do
not seem to aggregate in specific nursery areas, but later in the year the 0-group concentrate in
shallower parts of the range (Albert, 1993).
Movements and migrations: Silvery pout may form dense aggregations that can result in unusually
high catch rates. They migrate between deep areas, where they stay in winter, and shallower areas in
summer-autumn, but the pattern is not very pronounced. Also, they may have a tendency to gradually
move into deeper waters as they grow (Albert, 1993).
Trophic ecology: Both juveniles and adults feed almost exclusively on pelagic crustaceans
(euphausiids, amphipods, mysids, decapods and copepods), but small fish are also consumed
(Mattson, 1981; Mauchline and Gordon, 1984; Albert, 1993).
Exploitation
Silvery pout are an unavoidable bycatch in the industrial fisheries targeting Norway pout and blue
whiting. They are also a bycatch in fisheries for northern shrimp (Pandalus) in the Skagerrak and
North Sea, and can be used as bait.
0
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1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Gadiculus argenteus
0
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1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Gadiculus argenteus
20
32.2 Cod Gadus morhua
Linnaeus, 1758
DE: Kabeljau, Dorsch; ES:
Bacalao; FR: Morue; NL:
Kabeljauw; NO: Torsk
Lmax: 200 cm (Cohen et al., 1990) Photo: Sieto Verver
Data range: size 2140 cm; depth 11105 m
Catch rates of cod.
General
Apart from serving a delicious dish and being of great economic value or rather because of that ,
cod has been one of these creatures that has led to wars between countries as well as to international
cooperation for conservation. ‘Cod, a biography of the fish that changed the world by Kurlansky
(1998) describes its long history of influence on international developments very well. ‘Fishing for truth
by Finlayson (1994) provides a lot of insight in the world of scientific assessments, political inadequacy
to deal with important management problems, and the power of public opinion. There is a vast and
ever-growing amount of scientific literature relating to cod that is becoming increasingly hard to digest.
Here, there is only space for a brief overview and we apologise to those whose findings have been
omitted.
Taxonomy and identification: Although Linnaeus originally placed many members of the family in the
genus Gadus, it is currently only represented by three species: Atlantic cod Gadus morhua, Pacific
cod G. macrocephalus and Greenland cod G. ogac. Based on morphological characteristics, three
subspecies of G. morhua have been recognized: G. morhua morhua is the most widespread,
inhabiting both the western and eastern sides of the Atlantic, G. morhua callarias is restricted to the
Baltic Sea and G. morhua marisalba is only found in the White Sea (Svetovidov, 1986). The most
obvious distinction between the two subspecies found in the Atlas area is that the anterior processes
of the swimbladder of G. m. callarias are relatively long and curled at the tip. However, neither a
fisherman nor a scientist could tell from the outside whether a cod caught in the Belt Seas belonged to
one subspecies or the other. Recent synonyms include Gadus callarias.
Cod have three dorsal fins, all close together at the base, and two anal fins. The first anal fin originates
beneath or behind the interspaces between the first and second dorsal fins. The upper jaw is slightly
21
longer than the lower, which has a prominent barbel. Late post-larvae and newly-settled demersal
juveniles have characteristic ‘chess board’ markings. The background colouration of older cod can be
reddish, greenish or sandy brown, depending on the habitat, with darker mottling on the back and
sides and a prominent, pale lateral line. The ventral surface is white.
Biogeographical distribution: Cod is found throughout the boreal region of the North Atlantic; in the
west from North Carolina to Labrador, around Greenland and Iceland, and in the Northeast Atlantic
from the northern part of the Bay of Biscay up to Spitsbergen and Novaya Zemlya (Svetovidov, 1986).
Survey data
Spatial distribution: Cod occur throughout the Atlas area, but clearly reach their southern limit off
Brittany. On average, the highest catch rates are restricted to the Baltic Sea, the Kattegat/Skagerrak,
and the German Bight. Catch rates in the North Sea and just south of Dover Strait are somewhat
lower, but south of 49N catches drop remarkably. However, the distribution is more or less
continuous, without sharp separations that correspond to current management units (see Stock
structure),
Depth distribution: Newly-settled demersal juveniles can be found close inshore even in depths <10 m.
The adults occur down to 500 m or more but the bulk of the catches in the Atlas area were within
depths <200 m. In the BSER, shallow waters appear to be largely avoided and a peak is reached at
5060 m. This might well be related to the lower salinity in the top layer.
Depth distribution by ecoregion.
Size distribution: The LFDs differ considerably among ecoregions. In the CSER, there were
proportionally fewer small fish (<25 cm) and more larger ones than in the NSER, which is dominated
by small cod. In the BSER, a single mode is present around 30 cm, with relatively few smaller as well
as few larger fish. Really big cod (>100 cm) were scarce throughout the Atlas area, the vast majority
measuring <50 cm. Small cod are particularly abundant in waters <20m deep.
Length distributions: by ecoregion (left), and by depth band (right).
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Gadus morhua
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Gadus morhua
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depth class
Gadus morhua
0.0
0.1
0.2
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lfd
length class (5 cm)
Gadus morhua
E
F
L
0
2
4
6
8
10
0 25 50 75 100 125
lfd
length class (5 cm)
Gadus morhua
<20 m
>20 m
22
The difference in spatial distribution of small (<25 cm, representing largely 0-group and 1-year-olds)
and large cod is clearly visible below###. Small cod are virtually absent offshore in the Celtic Sea and
particularly abundant on inshore stations in the German Bight, and also along the Skagerrak and in
the Kattegat. Large cod roam the entire shelf, avoid the inshore continental coast and are most
abundant in the Baltic Sea.
Catch rates of small (<25 cm) and larger (>=25 cm) cod.
Time series: In the CSER, abundance was particularly high in 1988, 1997 and also in 2013, the last
year of the series. In the NSER strong year classes were produced in the 1970s and 1980s, but since
the last peak in the catches in 1996, abundance has been low. The time series for the BSER is much
shorter but suggests a strong decline after a short revival during the first few years, but in recent
years, catch rates have picked up again.
Survey indices by ecoregion.
The overall downward trend in the NSER is associated with a tendency to leave the southeastern part.
The concentration of juveniles previously seen in the German Bight has nowadays disappeared
completely (see maps below###). These maps also suggest a strong recent increase in the BSER
compared to the 1990s.
Catch rates of cod by period: 19771989 (left), 19901999 (middle), and 20002011(right).
Biology
Habitat: Cod generally aggregate in loose shoals roaming both over the sea bed and in mid-water.
They do not show clear preferences for specific sediments but appear to stay mostly within the
continental shelf area. Large specimens can often be caught near wrecks, where they appear to have
0
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3
4
5
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Gadus morhua
0
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20
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Gadus morhua
0
1
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3
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Gadus morhua
23
a more sedentary life style. Based on annual variations in temperature fields in relation to cod
distribution during winter, there is no evidence that cod have a particular preferred temperature range
(Heessen and Daan, 1994), although larger ones seem to avoid shallow waters during summer. The
thermal niche ranges from 1.5 to 19°C, but is narrower (1 to 8°C) during the spawning season
(Righton et al., 2010). However, the tolerance appears to depend both on size and on gradual
acclimatisation (see also Box on p. ###). Small 0-group in the Waddensea can tolerate temperatures
up to 23C. In addition, cod occupy a wide range of salinities, from near-freshwater conditions in the
Baltic Sea to about 35 psu (Hedger et al., 2004).
BOX Temperature tolerance in cod: serendipity in practice
In the winter of 1979, the Dutch research vessel had collected a large number of live cod of all sizes in
its well for feeding experiments back home, when it met surface temperatures below zero during a
severe gale in the Skagerrak and had to head back because of black ice developing. Because the well
was constantly fed by water from outside, the temperature had dropped rapidly and upon checking, all
large cod >60 cm were already dead. The following morning, also the middle-sized cod were floating
at the surface, but all cod <25 cm happily survived this unforeseen experiment (Daan, pers. obs.).
Age, growth and maturity (see also Table ###): Cod in the Atlas area have the potential to live for >15
years and attain a length of 140 cm or more. However, because of heavy exploitation, individuals older
than ten years and larger than 100 cm have become exceedingly rare. Growth rates differ by area and
from year to year. For example, the average length of 2-year-old cod caught during IBTS surveys in
the years 19701980 varied between 32 cm and 44 cm (van Alphen and Heessen, 1984). Cod in the
southern North Sea grow somewhat faster initially but to a smaller ultimate size than those in the north
(Daan, 1974). The length-at-age in the Baltic Sea is substantially lower than in the North Sea (Bagge
et al., 1994). L50% varies both spatially and temporally (Yoneda and Wright, 2004). Some individuals
mature in their second year of life but it is not until the age of six years that all have become mature.
The proportion reaching sexual maturity at two years of age has increased between the 1970s and the
2000s in both the northwestern and southern North Sea (Wright et al., 2011b). Size and age-at-
maturity off the west coast of Scotland have decreased over the same period (Yoneda and Wright,
2004). Cod in the Baltic Sea mature at a smaller size (but at a similar age) to those in the North Sea
(Bagge et al., 1994).
Percentage maturity by age group of North Sea cod (data Q1 IBTS, 20002004).
Reproduction: Spawning is widespread throughout the Atlas area and the season extends from
January in the south to April in the north. The situation in the Baltic Sea is special: the western
population spawns in spring and the eastern population during summer (Bagge et al., 1994). In the old
days, only late-stage ‘cod-like’ eggs could be identified reliably to the species level (Daan, 1978), but
recent advances in molecular techniques have made unambiguous identification of the early stages
possible. The distribution of recently released cod eggs during an ichthyoplankton survey in 2004 (Fox
et al., 2008) shows main concentrations in the region of the Dogger Bank with smaller patches in the
German and Southern Bights and near the entrance to the Skagerrak. Smaller numbers were also
0
20
40
60
80
100
1 2 3 4 5 6
Percentage maturity
Age (year)
F
M
24
taken off the Moray Firth and to the east of the Shetland Islands. Although in general accordance with
earlier investigations (Daan, 1978), this 2004 survey suggests that the importance of a spawning area
off the northeast coast of England (Harding and Nichols, 1987) has declined considerably. In the Baltic
Sea, the eastern population spawns over the deeper troughs (Gotland Deep, Gdansk Deep, Bornholm
Deep), and the western population in the transition area between the Kattegat and the Baltic Sea
(Bagge et al., 1994). In westerly waters, cod spawn in the Bristol Channel, southwest of Ireland, in the
Irish Sea, the Firth of Clyde and the Minches (Brander, 1994; Dransfeld et al., 2004; Hislop, 1986).
Spawning takes place near the bottom or in mid-water (Harden Jones, 1968). During the so-called
‘gadoid outburst’ in the 1970s (Cushing, 1984), fishers reported unusual large and ‘clean catches of
ripe and running cod in the Southern Bight, suggesting that cod form dense aggregations during the
actual spawning event. Under aquarium conditions, males display to the females by erecting the
dorsal and anal fins and producing sounds (grunts) by vibrating the swim bladder (Brawn, 1961; Rowe
and Hutchings, 2006).
Cod is a batch spawner. In captivity, females shed their eggs in up to 19 batches, at intervals of 112
days (Kjesbu, 1989). The relationship between fecundity, length and weight varies with time and space
(Rijnsdorp et al., 1991). Around 1970, the relative fecundity in the southern and central North Sea was
approximately 500 eggs per g body weight and the relationship between fecundity and total length
(cm) was estimated as F = 1.3 *LT3.3 (Oosthuizen and Daan, 1974); thus, a 75 cm female produced
almost 2 million eggs. Recent investigations (Yoneda and Wright, 2004) indicate that cod from the
northwestern North Sea now mature at a smaller size and younger age and have a higher fecundity
than around 1970 (West, 1970). Weight for weight, fecundity of Baltic cod is substantially higher
(Botros, 1962; Schopka, 1971).
Early stages: Cod produce large numbers of small pelagic eggs (1.161.60 mm) that do not contain an
oil globule (Russell, 1976). They are difficult to distinguish visually from the eggs of other gadoids,
such as haddock, until they are in a late stage of development and the embryos have developed their
characteristic pigmentation. The eggs of Baltic cod are larger (up to 1.89 mm), to compensate in terms
of buoyancy for the low salinity at which spawning takes place. The interval between fertilization and
hatching depends on temperature, ranging from 16 days at 6°C to 7 days at 12°C (Geffen et al.,
2006). Larval abundance tends to peak within frontal zones with steep haline gradients (Munk et al.,
1999, 2002). As in many gadoids, the juveniles stay off the bottom in midwater after metamorphosis
(see Box on p. ###) and take to the bottom at a length of 57 cm. In the northwestern North Sea,
young cod are most abundant in relatively shallow water (<20 m), often close inshore (Gibb et al.,
2007) and may associate with macroalgae and other structurally complex habitats. Off the west of
Scotland the majority are found in sea lochs. In the southern North Sea, the largest concentrations of
juveniles occur close inshore on sandy bottoms along the continental coast. The preference of 0- and
1-group for shallow water or for rough and/or weedy ground makes it difficult to obtain reliable indices
of abundance from bottom-trawl surveys. The distribution pattern in the North Sea has changed
markedly during the last 30 years. In the 1980s, the highest concentrations were found in the
southeast, along the continental coast, off northeast England and in the Skagerrak and Kattegat.
Since then, the continental coast has almost completely lost its function as an important nursery area
(Lewy and Kristensen, 2009). Intermittent periods of high abundance of juvenile cod in the eastern
Skagerrak have been linked to an inflow of eggs and larvae from the North Sea (Svedang and
Svenson, 2006).
Movements and migrations: In some parts of their geographical range, cod undertake long feeding
and spawning migrations (e.g. between the Lofoten and the Barents Sea), but within the Atlas area
movements are much less extensive. In the Norwegian Deeps, seasonal migrations up and down the
slope have been observed (Bergstad, 1991). In the southern North Sea, immature cod aggregate in
shallow water during winter and move to deeper water during summer (Heessen, 1983), while mature
cod appear in the commercial catches in autumn and disappear completely next May. Deployment of
data storage tags (DST) has provided insight into their behaviour. In the southern North Sea, cod
make use of tidal streams to migrate northwards and eastwards in spring, whereas tidal stream
25
transport was rarely exhibited by cod released in the eastern English Channel (Righton et al., 2007).
Robichaud and Rose (2004) distinguish four migratory patterns of spawning cod: sedentary, accurate
homers, inaccurate homers and dispersers. Within the Atlas area, the majority of the spawning groups
is thought to be sedentary (Neat et al., 2006; Wright et al., 2006).
Trophic ecology: Larval cod of 28 mm in length feed mainly on the nauplii and copepodite stages of
copepods (Last, 1978). After metamorphosis, the 0-group continue to feed mainly on copepods and
euphausiids but the diet changes rapidly and at a length of 5 cm they feed predominantly on fish
(Robb and Hislop, 1980). Kept alive in a tank on board, the larger 0-group fish were seen with the tails
of smaller individuals sticking out of their mouths, the population shrinking rapidly (N. Daan pers. obs.).
Once the juveniles have settled on the bottom, at a length of 57 cm, the diet is once again dominated
by crustaceans (including crabs and shrimps) but as they grow, fish becomes increasingly important.
Many of the prey taken by cod are of commercial importance, such as Crangon sp., Nephrops,
gadoids, sandeels, flatfish and clupeoids (Daan, 1989; Hislop, 1997). However, cod are not only
predators, but also scavengers. At least part of the fish found in stomach contents could easily
originate from discards. In the Baltic Sea, juveniles feed mainly on invertebrates (crustaceans and
polychaetes) and the adults on sprat and herring, although benthic isopods and polychaetes are also
important prey (Bagge et al., 1994). See also Box on p. ###.
Diseases and parasites: In some areas on both sides of the Atlantic, cod are heavily infected with
larvae of the nematode Pseudoterranova decipiens (known as sealworm), particularly in regions where
grey seals, their definitive hosts, are abundant (Rae, 1963; Marcogliese and McLelland, 1992). The
parasites live mostly in the liver or around the gut, but may also penetrate the flesh, necessitating their
removal before the fish can be sold for human consumption.
Stock structure: Genetic studies indicate that there are several sub-populations of cod within the Atlas
area. Microsatellite analysis has suggested that there are four genetically distinct populations in the
North Sea: near Bergen Bank, in the Moray Firth, near Flamborough Head and in the Southern Bight
(Hutchinson et al., 2001). Tag-recapture experiments indicate that there may be several resident
spawning groups of cod to the west of Scotland (Firth of Clyde, Minch; Wright et al., 2006). However,
from the continuous distribution of cod over the entire area and the presence of strayers as shown by
tagging experiments, the borders between these sub-populations must necessarily be rather vague.
For management purposes, seven stock units are distinguished: eastern and western Baltic Sea,
North Sea (including the Kattegat and the eastern Channel), West of Scotland, Celtic Sea, Irish Sea
and Rockall. This division is not necessarily based on population structure, but rather a reflection of
the necessity of managing fisheries on the basis of traditional fishing rights.
Exploitation
Cod has been exploited on both sides of the Atlantic for centuries as an important target as well as a
bycatch species in almost all gears used in demersal and pelagic fisheries throughout the area. The
main gears are otter trawls, pair trawls, gill nets and, in some areas, longlines. It is also favoured in
many recreational fisheries.
Catches in the Baltic Sea dropped from 400 thousand t in 1984 to 50 thousand in recent years and
from 75 thousand in the 1970s to 20 thousand t for the eastern and western stock, respectively. Total
catches (including discards) in the North Sea peaked at about 350 thousand t in the 1970s and early
1980s, during the time of the ‘gadoid outburst’ (see Box on p. ###). Thereafter, catches gradually
declined to a level of 5070 thousand t during the 2000s. The catches in the other management areas
have always been much smaller, but show also sharp declines. These declines have been attributed
to overfishing: the increase in fishing mortality resulted in a spawning stock biomass that was too small
to produce enough juveniles to replace the losses.
In an attempt to reverse the decline in spawning stock biomass in northern European seas an
international Cod Recovery Plan was initiated in 2004. Measures introduced under the Common
Fisheries Policy included increases in mesh size, seasonal area closures and a considerable reduction
26
in fishing effort. The large reduction in fishing mortality did help to increase the abundance of adult cod
in some areas, but there is still a long way to go before the fisheries in all areas will profit from these
measures.
BOX The gadoid outburst
From the late 1960s until the late 1980s several exceptionally strong year classes recruited to the
North Sea cod stock. This succession of strong year classes caused a rapid increase in both biomass
and landings. Because similar patterns were observed at the same time in other Gadidae (haddock,
with a strong year class in 1962 and an even stronger one in 1967; whiting; saithe), this event has
been called the gadoid outburst (Cushing, 1984). The causes are still obscure (Hislop, 1996). Some
explanations favour environment-induced changes in plankton abundance, while another explanation
links the outburst to over-exploitation and poor recruitment of the pelagic fish stocks. It is worth
pointing out that the application of Virtual Population Analysis (VPA) to commercial catch-at-age data,
which provides estimates of the absolute numbers and biomass of cod, haddock and whiting, began in
the early 1960s, coincident with the start of the gadoid outburst. The VPA time series for these three
species show a more-or-less continuous decline in the biomass, giving the impression that their stocks
may have decreased to unusually low levels. However, considered from an historical perspective it
has been postulated (Holden, 1991; Pope and Macer, 1996) that the decline in biomass observed
during the 1980s and 1990s might be regarded as a return to ‘normal’ levels after a period of
exceptionally high abundance. This interpretation now seems to have been too optimistic: in cod, for
example, the decline in spawning stock biomass (SSB) continued into the mid 2000s, reaching an
historical low point in 2006, while fishing mortality steadily increased until the end of the 1990s (ICES,
2014). These were symptoms of a stock in serious trouble. Fishing mortality has been decreasing
since 2000 and SSB has increased in the last few years but is still well below what is considered a
biologically ‘safe’ level.
27
BOX Pelagic 0-group Gadoid Surveys
All marine Gadidae in the Atlas area have pelagic eggs. After metamorphosis the juveniles remain in
the upper water layer, usually above the thermocline. The duration of the pelagic phase varies
between species. It is relatively short in cod, which disappear from the water column at a length of 6 or
7 cm, but considerably longer in whiting. Haddock and Norway pout make diel vertical migrations
between the upper and lower water layers before becoming largely demersal (Bailey, 1975).
During 19741983, coordinated international surveys using a fine-meshed pelagic trawl were
undertaken in late June/early July to map the abundance and distribution of the pelagic 0-group
stages of cod, haddock, whiting, and Norway pout in the northern and central North Sea (Holden,
1981). The main reason for these surveys was to find out if year-class strength was already fixed at
this early stage of development, but that turned out not to be the case. Nevertheless, they provided
valuable information on the spatial distribution.
The 10-year average for each species is shown in Figure ###. The northern North Sea between the
Shetlands and Norway apparently serves as an important pelagic nursery for all species, with another
hotspot north of Scotland. The pelagic nurseries of cod and whiting, and to a lesser extent haddock,
stretch southeastward to the Danish coast as well as in southwestern direction along the British coast.
In the shallow waters of the German Bight, cod were less abundant than whiting; it may have been the
case, that young cod in this area had already settled on the bottom by the time of the surveys.
Average catch rates of pelagic 0-group cod, haddock, whiting, and Norway pout, 19741983 (Hislop et al., 1984).
28
32.3 Haddock Melanogrammus aeglefinus
(Linnaeus, 1758)
DE: Schellfisch; ES: Eglefino; FR: Eglefin; NL:
Schelvis; NO: Hyse
Lmax: 112 cm at Iceland (Wheeler, 1978)
Data range: size 387 cm; depth 61105 m
Catch rates of haddock.
General
Haddock is typically a British food fish, sold fresh, smoked, frozen, or dried. In Scotland, it is a major
constituent of ‘fish and chips’, while Norwegians turn it into excellent fiskeboller. Authorities say that
haddock is not good for salting. So, if not sold fresh, it is either dried or smoked. The cold-smoked
Finnan haddie is served for breakfast, poached in milk. Not a bad idea after a heavy night.
Taxonomy and identification: The genus is represented by a single species. There are three dorsal
and two anal fins. The first dorsal fin is triangular, with long fin rays. The lower jaw is markedly shorter
than the upper and carries a short barbel. The snout extends beyond the mouth, which is directed
downwards when protruded, in keeping with the generally benthic diet. The dorsal surface is charcoal
grey, the flanks greyish-silver, and the belly white. There is a conspicuous rounded black ‘thumbprint’
between the pectoral fin and the first dorsal fin. The lateral line is dark (Wheeler, 1969). A recent
synonym is Gadus aeglefinus.
Biogeographical distribution: The distribution In the eastern Atlantic extends from the northern part of
the Bay of Biscay to Spitsbergen, the Barents Sea and Iceland, including Rockall Bank and the
Faroes. In the northwestern Atlantic, haddock inhabits shelf waters from Georges Bank to
Newfoundland (Svetovidov, 1986).
Survey data
Spatial distribution: In the North Sea both mature and immature haddock occur mainly in the northern
and central areas. In general, the southerly border of the distribution extends from northeast England,
along the northern edge of the Dogger Bank to the Skagerrak and Kattegat, closely following the 50 m
depth contour. However, when strong year classes are born, the distribution of juveniles may extend to
the more shallow areas in the south (ICES, 1976). It is absent from all but the extreme westerly part of
29
the Baltic Sea, but abundant in the shelf waters west of the British Isles, including the Irish Sea. High
catch rates were also recorded at Rockall, which presumably represents an isolated population.
Haddock is markedly less common in the most southerly part of the Atlas area.
Depth distribution: Found mainly in the depth range 50200 m with a peak around 100 m. Only in the
BSER do they occupy lesser depths (<40 m).
Depth distribution by ecoregion.
Size distribution: The majority of the haddock caught in the surveys were in the length range 1030
cm, i.e. individuals of <3 years old. The size distributions in the CSER and NSER are virtually similar,
but in the BSER the catches contained markedly larger fish. No effect of depth on the size distribution
could be found, the patterns below and above 100 m deep being almost the same.
Length distributions: by ecoregion (left), and by depth band (right).
Time series: There are no obvious trends in overall abundance in any of the three areas except that
the apparent increase during the earlier Baltic Sea surveys stopped abruptly in 1997. From time to
time, for reasons that are not well understood, haddock produces exceptionally strong year classes
such as those born in 1962, 1967, 1974 and 1999. These successful year classes result in short-lived
increases both in overall abundance and spawning stock biomass.
Survey indices by ecoregion.
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Melanogrammus
aeglefinus
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Melanogrammus
aeglefinus
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Melanogrammus
aeglefinus
0.0
0.1
0.2
0.3
0.4
015 30 45 60 75 90
lfd
length class (5 cm)
Melanogrammus
aeglefinus
0
2
4
6
8
0 10 20 30 40 50 60 70 80 90
lfd
length class (5 cm)
Melanogrammus
aeglefinus
<100 m
>100 m
0
1
2
3
4
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Melanogrammus aeglefinus
0
2
4
6
8
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Melanogrammus aeglefinus
0
2
4
6
8
10
12
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Melanogrammus aeglefinus
30
Biology
Habitat: Haddock is a demersal species, found mainly over sandy and muddy substrates. In the North
Sea the bulk of the population occurs in depths of between 75 and 125 m, at bottom temperatures
>6°C and salinities >34.5 psu (Hedger et al., 2004).
Age, growth and maturity: The general relationship between age and length (left panel in figure
below###) masks the fact that growth rates vary considerably among regions and years (Jones, 1983).
After the first year of life females are, on average, larger than males, reflecting the maturation of males
at a younger age. Haddock has the potential to live for about 15 years but, because of heavy
exploitation, few survive for more than six or seven years. More males than females become mature
during the first two years of life but >90% of the three-year-olds of both sexes are currently mature
(right panel in figure below###). The proportion of fish reaching sexual maturity by age has increased
markedly between the 1980s and the early 2000s: thus, the percentage of mature 2-year old females
in the western North Sea increased from 14 to 65% and in the eastern North Sea from 14 to 48%.
Around 70% of three-year olds were mature in the 1980s compared to about 97% in recent years
(Wright et al., 2011a).
Mean length (left) and percentage maturity (right) by age group of North Sea haddock (data Q1 IBTS, 2000
2004).
Reproduction: The spawning season extends from March to May. Haddock is a batch spawner. The
mean duration of spawning activity of a group of captive fish was 33 days (range 1959) during which
an average of 17 batches (range 1025) were produced (Hislop et al., 1978). Two-year-old, first-time
spawners spawn much later than older age-classes and the survivorship of their offspring is
comparatively low (Wright and Gibb, 2005). Principal spawning areas in the North Sea occur off the
northeast coast of Scotland, to the east and southeast of the Shetland Islands, and to a lesser extent
near the entrance to the Skagerrak/Kattegat. In the west, a major spawning area exists off the
northwest coast of Scotland, with smaller spawning grounds in the Minch, the northwestern Irish Sea
and the Celtic Sea (Saville, 1959; Dransfeld et al., 2004; Taylor et al., 2007). Haddock also spawn at
Rockall and on Porcupine Bank. Males exhibit a courtship display by erecting the dorsal and anal fins,
and altering the pigmentation of the flanks. In addition, they produce a variety of sounds by the action
of a pair of ‘drumming muscles’ on the swim bladder (Hawkins et al., 1967). The relationship between
fecundity (F) and size of North Sea haddock in the late 1970s is given by F = 0.90 *LT3.4 (Hislop and
Shanks, 1981; for an early study see Raitt, 1933). Thus, a 40 cm female produced approximately 275
thousand eggs. Since that time, the relative fecundity of 2- and 3-year-old haddock has increased
(Wright et al., 2011a).
Early stages: The eggs are pelagic, measure 1.21.7 mm in diameter and have no oil globule (Russell,
1976). Hatching takes from one to three weeks, depending on temperature. In an extensive study,
most of the larvae in the 611 mm size range were found at mid depths in the water column (2550 m)
in daytime, whereas they were more dispersed at night. The largest larvae (>10 mm) were found
higher in the water column, reacting to turbulence in the surface layer: they approached the surface
under calm conditions but moved deeper when wind speed increased (Gallego et al., 1999). After
0
10
20
30
40
50
1 2 3 4 5 6
Mean length (cm)
Age (year)
F
M
0
20
40
60
80
100
1 2 3 4 5 6
Percentage maturity
Age (year)
F
M
31
metamorphosis, 0-group haddock spend the first few months of life in mid-water above the thermocline
(see Box on p. ###). However, after adopting a demersal way of life at a size of 48 cm (Bailey, 1975:
Bromley and Kell, 1999), the distributions of the juveniles and adults overlap almost completely.
Although discrete nursery areas do not exist, high densities of 0-group do occur in the Skagerrak, east
of the Shetlands, off the east and northeast coasts of Scotland and north of the Hebrides. On the basis
of otolith microchemistry, it has been shown that the proportional contribution to the adult population of
each of four areas around Scotland varied from year to year (Wright et al., 2010). Although dispersal
of larvae away from the spawning grounds is generally limited, modelling studies suggest that a
substantial component of the eggs spawned off the Scottish west coast are transported into the North
Sea (Heath and Gallego, 1997).
Movements and migrations: Haddock is not known to make extensive migrations, but a seasonal
migration has been observed locally between relatively shallow areas in summer and deeper waters in
winter (Albert, 1991). Tag-recapture experiments in Scottish waters indicate a northerly movement
along the east coast and some interchange between the North Sea and the west coast, the majority of
movements being from east to west (Jones, 1959; Jones and Cross, 1965).
Trophic ecology: The larval stages feed mainly on immature copepods (Russell, 1976). Pelagic
juveniles (length range 30139 mm) eat copepods, euphausiids, decapod crustacean larvae,
appendicularians and larval fish (Robb and Hislop, 1980). Newly-settled juveniles eat pelagic
organisms (e.g. euphausiids) as well as a variety of benthic organisms, including polychaete worms,
crustaceans, molluscs and echinoderms. More than 50% of the diet of larger haddock (>35 cm)
consists of fish such as sandeels, Norway pout, long rough dab, gobies, sprat and herring (de la
Villemarque, 1985; Cranmer, 1986). At the right time and place, haddock may feed heavily on herring
eggs (‘spawny haddock’; Bowman, 1928), thereby potentially affecting the abundance of herring
(Richardson et al., 2011). More generally, shoals of haddock appear to feed on whatever is locally
abundant. See also Box on p. ###.
Diseases and parasites: Haddock is intermediate host to the nematodes Anisakis simplex (herring
worm or whale worm; Smith, 1984) and Pseudoterranova decipiens (cod worm or seal worm;
Marcogliese and McClelland, 1992). The former is normally found only in the body cavity but larval
Pseudoterranova may invade the flesh and pose a potential health threat to humans. The copepod
Lernaeocera branchialis is regularly found attached to the gills and this infection is associated with
lower body condition (Kabata, 1958) and reduced fecundity (Hislop and Shanks, 1981).
Stock structure: Although North Sea haddock is assessed separately from the populations west of the
British Isles, the separation is largely artificial because a genetically continuous race extends around
the Hebrides, the Northern Isles and the Scottish east coast. In contrast, the western and eastern
populations within the North Sea,are genetically distinct (Jamieson and Birley, 1989). Not a great deal
is known about the stock structure west of the British Isles, although the population at Rockall appears
to be isolated from the shelf populations.
Exploitation
Haddock is of considerable commercial importance. Most of the catch is taken in a mixed fishery
undertaken mainly by Scottish seiners and light trawlers. The bulk of the catch is landed for human
consumption but discarding rates are high in some fisheries (in particular the Nephrops fishery).
Landings of industrial fisheries for Norway pout also contain a variable amount of haddock. Total
catches from the North Sea and West of Scotland have declined more or less continuously since the
gadoid outburst of the late 1960s and early 1970s. This decline can be attributed to overfishing (and
associated low levels of recruitment) and, in recent years, to an increase in minimum mesh size,
introduced as part of the Cod Recovery Plan.
32
32.4 Whiting Merlangius merlangus
(Linnaeus, 1758)
DE: Wittling; ES: Merlan; FR: Merlan; NL:
Wijting; NO: Hvitting
Lmax: 70 cm (Wheeler, 1978)
Data range: size 274 cm; depth 1551 m
Catch rates of whiting.
General
Whiting have a problem. Although the flesh of whiting is as good as that of any other gadoid, they are
undervalued by most nations. Only in France and the UK do they get the respect they deserve. For
instance, in the 1960s and 1970s, 7090% of the catch in numbers taken by Dutch vessels has been
discarded. Only 30% of these were actually below the legal minimum landing size of 24 cm, but there
was simply no market for so many small whiting. Not enough cats and pure waste (Daan, 1976).
Taxonomy and identification: Whiting, another representative of a mono-specific genus, is a medium-
sized codfish with three dorsal and two anal fins. The first anal fin is long and originates beneath the
centre of the first dorsal fin. The lower jaw is shorter than the upper, the jaws somewhat pointed and
with prominent teeth. The dorsal surface is sandy to greenish-blue, the sides and belly are
conspicuously white and there is a dark spot at the base of the pectoral fin (Wheeler, 1978). Two
subspecies have been identified: M. merlangus merlangus without, and M. merlangus euxinus with a
chin barbel (Svetovidov, 1986). Recent synonyms: Gadus merlangus, Odontogadus merlangus.
Biogeographical distribution: The range of M. m. merlangus extends from the Barents Sea and
southeast Iceland to the western Mediterranean Sea, where it is uncommon. M. m. euxinus, occurs in
the Black Sea, the Sea of Azov, the Sea of Marmara and the Adriatic and Aegean Seas (Svetovidov,
1986).
Survey data
Spatial distribution: Whiting is one of the most widely distributed and most abundant gadoid species in
the Atlas area. It is found in high numbers throughout the North Sea, to the east in the
Skagerrak/Kattegat and in the western part of the Baltic Sea, but also all along the shelf to the west of
33
the British Isles. Whiting becomes less abundant in the offshore areas (Rockall and Porcupine Bank)
and in the most southwesterly region.
Depth distribution: The depth distribution ranges from extremely shallow inshore waters (<10 m) to a
maximum of 550 m, but by far the greatest numbers occur in the range 30100 m.
Depth distribution by ecoregion.
Size distribution: Although whiting has the potential to grow to more than 60 cm, the vast majority of
the population is made up of much smaller individuals (<40 cm). There are no obvious differences
between the size compositions in the three ecoregions, although the catches in theBSER included a
higher proportion of relatively large whiting (>30 cm). Whiting are on average smaller at depths <100
m than at greater depths.
Length distributions: by ecoregion (left), and by depth band (right).
The distribution of small (<20 cm; corresponding largely to 0-group and 1-year-olds) whiting is quite
different from the larger ones. Whereas the Kattegat and the German Bight are hotspots for the
juveniles, larger whiting are concentrated on the western side of the North Sea, particularly off north
Scotland, northeast England, and in the Channel area. Also in the CSER, the concentrations show
little overlap.
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Merlangius
merlangus
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Merlangius
merlangus
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Merlangius
merlangus
0.0
0.5
1.0
0 25 50 75 100
length class (5 cm)
Merlangius
merlangus
E
F
L
0
2
4
6
8
10
0 10 20 30 40 50 60 70
lfd
length class (5 cm)
Merlangius
merlangus
<100 m
>100 m
34
Catch rates of small (<20 cm) and larger (>=25 cm) whiting.
Time series: Indices of total abundance indicate two years of high abundance in the CSER during the
1990s, after which abundance has fluctuated around the average level, with 2013 standing out as a
year of relatively high abundance. In the NSER, an increase in abundance during the 1980s has been
followed by a decrease in the next two decades. Since 2002, catches have been below the long-term
average. There is no discernible trend in the more limited time series for the BSER, but 2013 was the
lowest on record. It seems surprising that whiting, a relatively warm-water gadoid, has not shown a
progressive increase in abundance in response to recent increases in water temperatures.
Survey indices by ecoregion.
The change in abundance in different areas can be followed in the distribution maps by three periods.
The western area has clearly undergone a major increase all around Ireland and also the Channel
area is doing well. In contrast, abundance in the northern North Sea has declined markedly.
Catch rates of whiting by period: 19771989 (left; no data for BSER and part of CSER), 19901999 (middle), and
20002011(right).
Biology
Habitat: The first two or three months of life are spent near the surface where the pelagic juveniles
often associate with jellyfish, in particular hair jelly Cyanaea sp. (Thiel, 1978; Hay et al., 1990).
Thereafter, they adopt a mainly demersal way of life although whiting also occurs in mid-water. Older
juveniles (0- and 1-group) are often abundant in coastal waters, including estuaries. Adults occur in
deeper water, mainly over sandy and muddy substrates.
-14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18 20 22 24
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Average n/hour
0 to 0.0001
0.0001 to 0.1
0.1 to 1
1 to 10
10 to 100
100 to 1000
1000 to 10000
10000 to 1000000
Merlangius merlangus <20cm
-14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18 20 22 24
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Average n/hour
0 to 0.0001
0.0001 to 0.1
0.1 to 1
1 to 10
10 to 100
100 to 1000
1000 to 10000
10000 to 1000000
Merlangius merlangus >=20cm
0
2
4
6
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Merlangius merlangus
0
2
4
6
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Merlangius merlangus
0
1
2
3
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Merlangius merlangus
35
Age, growth and maturity: Whiting grow slowly after the first year of life (left panel in figure below###),
as usual for a species that reaches sexual maturity at a young age. Still, regional variation in growth is
considerable and the age of a 30 cm North Sea whiting may range from two to six years (Daan, 1989).
The potential maximum age is in the order of 1215 years, but few fish surpass the age of six because
of heavy exploitation. Some females and a larger proportion of males mature at the end of their first
year of life and approximately 70% of the two-year-olds of both sexes are mature (right panel in figure
below###). The situation is broadly similar in the Irish Sea (L50% being 19 and 22 cm respectively), but
the percentage of one-year-old males reaching maturity has markedly increased since 1997 (Gerritsen
et al., 2003).
Mean length (left) and percentage mature (right) by age group in February 20002004 (NS- IBTS data).
Reproduction: The spawning season is prolonged, commences in January in the English Channel and
continuing until June or early July in the northern North Sea. Eggs are produced in batches, individual
females spawning over a period of 1214 weeks in captivity (Hislop, 1975). Like in cod and haddock,
males court females by displaying their dorsal and anal fins, but in contrast males do not produce
sounds (Hawkins, 1970). Whiting spawn mostly in water <100 m deep. Whiting is an extremely fecund
species (F = 5.85 x LT3.25), with a 35 cm female producing approximately 600 thousand eggs
(Messtorff, 1959; Hislop and Hall, 1974). Relative fecundity is also high (15002000 eggs per g gutted
weight; Hislop, 1984).
Early stages: Compared to other gadoids, the pelagic eggs are relatively small (diameter 0.971.32
mm; no oil globules; Russell, 1976). Hatching takes place after about ten days, depending on the
temperature. Information on larval distribution is patchy. Because of the wide area and the long
spawning season, early stages have been poorly sampled during ichthyoplankton surveys targeted at
species of greater commercial importance. However, concentrations of eggs and larvae have been
found off the northeast coast of Scotland and along the Dutch and German coasts (Taylor et al.,
2007), as well as in the western and eastern parts of the English Channel. To the west, whiting spawn
in the Minches, the Firth of Clyde and Irish Sea (Garrod and Gambell, 1965) and in the Celtic Sea.
Concentrations of larvae also occur off the north and south coasts of Ireland (Dransfeld et al., 2004).
Demersal juveniles (0-group) are found mainly in water <50 m deep, including estuaries. In the North
Sea, the locations where 0-group are concentrated vary on an annual basis and nursery areas do not
seem to be fixed geographically. West of the British Isles, the juveniles are found in sea lochs and the
shallow parts of the Celtic and Irish Seas (Gordon, 1977; Nagabhushanam, 1964).
Movements and migrations: Tag-recapture experiments have shown that whiting do not make long
migrations, the majority being recaptured <110 km (i.e. less than one degree latitude) away from the
release site (Tobin et al., 2010). Limited north/south movements have been reported along the
Scottish coast as well as inshore-offshore movements at Shetland (Hislop and MacKenzie, 1976;
Tobin et al., 2010). Part of the Skagerrak population is thought to move into the northeastern North
Sea to spawn (Knudsen, 1964). Whiting tagged in coastal waters in the southwestern North Sea in
summer moved offshore and into the eastern English Channel in winter (Williams and Prime, 1966).
Overall, spatial interchange appears to be limited between the northern and southern North Sea,
0
10
20
30
40
1 2 3 4 5 6
Mean length (cm)
Age (year)
F
M
0
20
40
60
80
100
1 2 3 4 5 6
Percentage maturity
Age (year)
F
M
36
between the northeastern North Sea and west of the British Isles, between the Irish Sea and the Firth
of Clyde and between the western and eastern parts of the English Channel (Tobin et al., 2010;
Garrod and Gambell; 1965; Hislop, 1986).
Trophic ecology: Whiting is an active predator that feeds on and near the sea bed as well as in mid-
water (sometimes only a few metres from the surface). The larvae start feeding at a length of 2.4 mm,
mainly on juvenile copepods (Last, 1978). Pelagic juveniles (10100 mm) feed on copepods,
euphausiids, appendicularians and larval fish (Robb and Hislop, 1980). The information on the diet of
older whiting is considerable (Hislop et al., 1991). It consists mainly of crustaceans and fish, although
polychaete worms and squid can be important prey in some areas and seasons. The proportion of fish
increases with body size, reaching about 80% in 30 cm fish. The principal invertebrate prey items
include mysids, amphipods, euphausiids and crangonid shrimps. Among the fish prey, sandeels, sprat,
small herring and gadoids, including whiting and Norway pout, are the most important species. Whiting
is one of the major predators on commercial North Sea fish species (ICES, 1991) as well as on brown
shrimp (Tiews, 1978). See also Box on p. ###.
Diseases and parasites: Parasites include the copepods Lernaeocera branchialis and Clavella
adunca, the larva of the cestode Gilquinia squali, which is found in the eye, the trematode
Diclidophora merlangi, found on the gills (Arme and Halton, 1972) and the protozoans Myxidium sp.
and Ceratomyxa sp., which occur in the gall bladder (Kabata, 1967). Larvae of the nematode Anisakis
simplex may be found in the body cavity (Smith, 1984). Parasitological studies have provided some
insight into stock structure.
Stock structure: Tag-recapture experiments and analysis of otolith microchemistry suggest that the
whiting population in the Atlas area is made up of a large number of sub-groups (Tobin et al., 2010).
Genetic studies indicate that the whiting in the Bay of Biscay can be differentiated from those in the
Atlantic waters west of the British Isles, which represent a metapopulation (Charrier et al., 2007). The
situation in the North Sea is more complex. Tag-recapture experiments and parasitological studies
(Kabata, 1967; Hislop and MacKenzie, 1976; Lang, 1990) suggest that there is little interchange of
whiting between the northern and southern parts of the North Sea and between inshore and offshore
areas. There may, however, be some movement of older whiting from the Moray Firth to Shetland and
thence to deeper waters to the east (Hislop and MacKenzie, 1976). Genetic studies have given
conflicting results, varying between no structure at all (Child, 1988) and the identification of at least
three distinct stocks (Charrier et al., 2007). However, given the continuous distribution and the
absence of well-defined spawning areas, it is difficult to imagine how these distinct units could be
maintained.
Exploitation
Whiting are caught in mixed demersal roundfish or flatfish fisheries, Nephrops fisheries and as a
bycatch in the industrial fisheries for sandeel and Norway pout. Most of the landed catch is for human
consumption, but substantial quantities, often larger than the landed catch (Daan, 1976), may be
discarded at sea. Total catches (including discards) in the North Sea and eastern English Channel
have decreased markedly during the last two decades from about 50 thousand t per annum in the
early 1990s to <20 thousand t since 2003. Although recruitment declined during this period, other
factors have also contributed. Thus, measures taken since 2002 to aid the recovery of cod stocks
have influenced the amount and distribution of fishing effort. Furthermore, minimum mesh sizes have
increased and industrial fisheries have reduced considerably since 1995. The decline in whiting
catches in the Irish Sea, Celtic Sea and on the grounds west of Scotland has been even more drastic
and the stocks in these areas in 2011 were close to historically low levels.
37
32.5 Blue whiting Micromesistius poutassou (Risso, 1827)
DE: Blauer Wittling; ES: Bacaladilla; FR: Merlan bleu; NL: Blauwe wijting; NO: Kolmule
Lmax: 50 cm (Monstad, 2004)
Data range: size 251 cm; depth 11763 m
Catch rates of blue whiting.
General
Blue whiting is a meso-pelagic gadoid from deeper waters that may be found in massive schools near
the edge of the continental shelf. Two comprehensive publications by Bailey (1982) and Monstad
(2004) thoroughly describe all aspects of the biology and exploitation. The biology sections essentially
summarize these publications without references, unless additional information is available.
Taxonomy and identification: Within the genus, blue whiting is the only species in the northern
hemisphere. Its congener, the southern blue whiting M. australis, occurs in the southwest Atlantic,
southwest Pacific and in the Bellingshausen Sea (Bailey, 1982). Blue whiting is a slender-bodied fish,
readily identifiable by three dorsal fins of which the first two have rather short bases compared to other
gadoids, by its long first anal fin that originates in front of the first dorsal fin, by its pale, bluish colour
and by the black mouth cavity. The second and third dorsal fins are widely spaced (Wheeler, 1969,
1978; Svetovidov, 1986; for meristics see Pethon, 2005). Blue whiting is the only gadoid for which
external sexual dimorphism has been described: males possess thin, elongated pelvic fins, while
these are short and blunt in females (Andersen and Jakupstovu, 1978).
Biogeographical distribution: In the Northeast Atlantic, blue whiting inhabit the temperate waters of the
Gulfstream from Morocco northwards to Spitsbergen, extending northwestwards to Iceland and
southern Greenland, as well as into the Barents Sea. Their northern distribution is limited by the Polar
Front. Although the species has been reported from the Mid-Atlantic Ridge in the 1970s and 1980s
(Gerber, 1993), later investigations failed to find any specimen in that area (Sutton et al., 2008). It also
occurs in the Mediterranean Sea and may even range into the Black Sea (although this area appears
to be suboptimal because of its low salinity). Blue whiting also occur in a restricted area east of
Newfoundland (Wheeler, 1978).
Survey data
38
Spatial and depth distribution: As a meso-pelagic species, blue whiting predominantly inhabit depths
>200 m (preferentially residing at depths of 300500 m), but may occur demersally on and along the
continental shelf. Consequently, during bottom trawl surveys they are chiefly captured in those areas,
where the topography intersects with the depth preference, such as the shelf edge, oceanic banks like
Porcupine and Rockall Bank, and along the Norwegian Deeps. Juveniles can also regularly be found
in shallower waters of the Celtic Sea, as well as occasionally in the deeper areas of the North Sea and
rarely in the Kattegat.
Depth distribution by ecoregion.
Length distribution by ecoregion.
Size distribution: The LFDs have a bimodal length distribution in both the CSER and in the NSER.
However, the peaks in the CSER are in the 15 and 20 cm length classes, indicating that mostly 0- and
1-group were caught (Bailey, 1982), whereas the second peak in the NSER falls in the 25 cm class,
indicating adults. The 1-group appers to be largely absent.
Time series: Because of its chiefly meso-pelagic occurrence, time series of demersal trawl catches on
the continental shelf do not necessarily reflect changes in total abundance. Catch rates in the CSER
have generally been higher since the early 1990s with a peak in 2010. The NSER is also
characterized by higher abundance in the late 1990s and early 2000s with an incidental peak in 2009.
Both peaks could refer to a good yearclass 2009, which turns up in the NSER as 0-group and in the
CSER as 1-group.
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Micromesistius
poutassou
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Micromesistius
poutassou
0.0
0.5
1.0
010 20 30 40 50
lfd
length class (2 cm)
Micromesistius
poutassou
0
1
2
3
4
5
6
7
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Micromesistius poutassou
0
1
2
3
4
5
6
7
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Micromesistius poutassou
39
Survey indices by ecoregion.
Biology
Habitat: Blue whiting is a meso-pelagic species that only adopts a demersal behaviour in those areas
where the bottom topography intersects with its preferred depth stratum (Merrett, 1986).
Age, growth and maturity (see also Table ###): Blue whiting grow relatively fast during their first year
to a length of 1220 cm, reaching 2025 cm after 2 years. They reach an age of >12 years, at which
they are generally 3540 cm, but specimens of up to 50 cm have been reported (Monstad, 2004). Blue
whiting from the Mediterranean Sea grow to a smaller size (Linf = 28 cm) than fish from the North
Atlantic (Linf: 3145 cm). The fish become mature at a size of 2025 cm and at an age of 24 years
about 86% of the population has reached adulthood. However, some individuals may not mature
before they are 7 years old (ICES, 1995). Males tend to become mature at a slightly smaller size than
females.
Reproduction: During the main spawning season in March and April, the bulk of the stock is found in
the area west of the British Isles along the shelf edge between the Porcupine Bank area and the
Hebrides. However, spawning takes place along the entire European Shelf between Portugal
(Kloppmann et al., 1996) and west of the Shetlands, on Rockall Bank, and at the edge of the southern
Faroese Shelf. Spawning starts in the south in January and progresses northward as temperatures
increase to end in May at the Faroes. Fecundity estimates (F) are characterized by the following
relationship: F = 0.14 L3.74 (Bailey, 1982). Thus, the fecundity of a typical female of 30 cm would be 48
thousand eggs.
Early stages: The development of eggs and larvae has been described from artificially fertilized and
reared eggs (Seaton and Bailey, 1971). At a temperature of 1011°C (which would be slightly higher
than the ambient temperature in the ocean), larvae start hatching after 4 days. Most eggs are found at
depths of 300500 m, but they are sometimes observed at lesser depths, which could reflect local
upwelling. Larvae occur down to a maximum depth of 600 m and typically show a bimodal depth
distribution. Recently hatched larvae of 23 mm are found at greater depths, while larger larvae
migrate to 3050 m depth where they find a suitable feeding environment (Coombs et al., 1981;
Hillgruber et al., 1997; Hillgruber and Kloppmann, 1999, 2000; Kloppmann et al., 2001). Within the
major spawning area, larvae may drift either northwards or southwards, depending on the exact
spawning site. In this way, they get transported towards the nursery areas, which stretch in the north
from the Norwegian Deeps far into the Norwegian Sea and in the south into the Celtic Sea. The
divergence in drift patterns may constitute the basis for different sub-populations.
Movements and migrations: Blue whiting undertake long-distance migrations between nursery,
summer feeding and spawning areas. During summer and autumn, the major part of the stock is
distributed over the Norwegian Sea, predominantly in association with fronts where feeding conditions
are enhanced (Monstad and Blindheim, 1986). In some years, they may also migrate westwards into
deeper ocean basins. Juveniles can be found all the way along the Norwegian coast and in the
Barents Sea. It is only recently that these migration patterns are starting to become fully understood.
(Hátún et al., 2009a,b): a close correlation has been found between spawning distribution, post-
spawning migration, recruitment success and the strength of the sub-polar gyre. When this gyre is
widely extended, spawning activity is more confined to the shelf edge west of the British Isles and the
post-spawning migration would follow a more easterly path through the Faroe-Shetland Channel into
the Norwegian Sea. When the sub-polar gyre is weak and more restricted, spawning activity is less
confined and extends into the Rockall Trough and the Rockall Bank area, while the post-spawning
migration would follow a more westerly path across the Iceland-Faroe Ridge into the Norwegian Sea.
The latter conditions would have a positive effect on recruitment. The occurrence of blue whiting in the
Barents Sea may be related to the magnitude of the Atlantic inflow and recruitment (Heino et al.,
2008).
40
Trophic ecology: The diet of juveniles and adults comprises large zooplankton (calanoid copepods and
euphausiids), but also includes small cephalopods and larvae or juveniles of lanternfishes and
pearlsides. While partially planktivorous, blue whiting lack a gill lattice and are therefore viewed as
being inefficient plankton feeders. In the Barents Sea, they also feed on small forage fish such as
polar cod, capelin, and redfish. However, their major food consists of krill Meganyctiphanes norvegica
and large copepods, which are also the cause of the high infestation with Anisakis nematodes.
The larval diet consists chiefly of nauplii and early copepodite stages of various copepod species.
First-feeding larvae in the deeper areas of Porcupine Bank fed predominantly on minute planktonic
organisms, such as tintinnids and cyclopoid nauplii, while larger larvae that were retained over the
shallower areas of the bank profited from the high abundance of larger calanoid nauplii, which they
actively selected (Conway, 1980; Hillgruber et al., 1997, Hillgruber and Kloppmann, 1999).
Blue whiting is itself a forage fish that represents a major food source for many marine predators,
including hake, squid and particularly pilot whales. The relationship between variability in ocean
circulation, zooplankton production, blue whiting recruitment and pilot whale abundance in the
Northeast Atlantic has been thoroughly investigated by Hátún et al. (2009b).
Diseases and parasites: Most parasites are acquired from crustacean prey. The most conspicuous
ones are larvae of the nematode Anisakis simplex, which infect the body cavity and muscles of the
flanks and belly. Prevalence increases with age, but condition does not appear to be affected
(Büssmann and Ehrich, 1979). In contrast to northern waters, individuals caught south of the British
Isles are less or even not at all infected. Another common parasite is the coccidian Eimeria, which
deposits oocytes in the liver and affects the condition. Infestation rate with specific parasites has
nourished the discussion about the possible existence of different populations.
Stock structure: A species that occurs and spawns over such a vast area within a complex circulation
system would be expected to comprise several populations (Bailey, 1982). Early investigations have
focussed on morphometric and meristic characteristics, but these did not resolve the issue. Based on
morphological observations and potential drift patterns of larvae, a separation line between a northern
and a southern stock component has been postulated (Isaev and Seliverstov, 1991; Isaev et al.,1992).
Later on, larval drift models supported the hypothesis that divergent drift patterns (north- or
southwards) in the Porcupine Bank area could help to sustain different populations (Bartsch and
Coombs, 1997; Skogen et al., 1999). Retention areas above the Porcupine and Rockall Bank or the
Rockall gyre could serve as mechanisms enhancing the potential for population separation
(Kloppmann et al., 2001). Recent work on genetics (Mork and Giaerver, 1995; Ryan et al., 2005, Was
et al., 2008) corroborated a separation between a northern and a southern stock component, but also
highlighted the existence of rather isolated populations at the southern (Mediterranean Sea) and
northern (Barents Sea) extents of the distribution (Ryan et al. 2005). The possible existence of several
smaller (sub-) populations within the northern and southern stock components is supported by an
analysis of otolith microstructure (Brophy and King, 2007).
Exploitation
Despite its sheer abundance, commercial exploitation of blue whiting was non-existent prior to the
1970s, except for the occasional bycatch in the industrial fisheries for other pelagic species (Wheeler,
1969; Bailey, 1982). With the collapse of the large herring stocks in the North Atlantic by the end of the
1960s, the fishing industry sought new resources and started to focus on blue whiting. Because of the
high infestation rates with nematodes, the species was quickly ruled out as providing a potential
market for human consumption. Only in southern Europe can blue whiting be found at local fish
markets, partly because of lower infestation rates with nematodes. Consequently, the majority of the
catches has been turned into fish meal. In recent years, however, blue whiting is increasingly being
used for the production of surimi.
41
32.6 Pollack Pollachius pollachius
(Linnaeus, 1758)
DE: Pollack, Steinköhler; ES: Abadejo; FR: Lieu
jaune; NL: Pollak, Witte koolvis; NO: Lyr
Lmax: 130 cm (Wheeler, 1978)
Data range: size 6101 cm; depth 1370 m
Presence/absence of pollack. (Some records disappeared from the Baltic)
General
Pollack or lythe is a poorly known bentho-pelagic gadoid that is generally caught in small numbers
together with saithe. Apart from their distribution in deep water and on rocky ground, they like hanging
around wrecks. A foul haul because of a damaged trawl often yields a few pollack of a good size.
Pollack must not to be confused with Atlantic pollock, which name in North-America refers to saithe
Pollachius virens, or with Alaska pollock Theragra chalcogramma, which represents an entirely
different genus.
Taxonomy and identification: The genus Pollachius is represented by two species that both occur in
the Atlas area: saithe P. virens and pollack P. pollachius. Pollack has three dorsal and two anal fins.
The first anal fin is long, with its origin under the first dorsal fin. The interspaces between the dorsal
and anal fins are relatively long. The lower jaw clearly projects beyond the upper one and the lateral
-14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18 20 22 24
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
-14 -12 -10 -8 -6 -4 -2 0246810 12 14 16 18 20 22 24
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Pollachius pollachius
42
line is dark against a lighter gold-brown background and has an obvious curvature. Based on these
last two characteristics, saithe and pollack can easily be distinguished.
Biogeographical distribution: The distribution is restricted to the Northeast Atlantic, where it may be
found from the Portuguese continental coast northwards around the British Isles, into the Skagerrak
and along the Norwegian coast, where it is fairly common up to the Lofoten Islands. Pollack is rare at
the Faroes and Iceland, and in the Baltic Sea (Svetovidov, 1986). Recently, catches from as far north
as Bear Island have been reported in Norwegian statistics.
Survey data
Spatial distribution: In the NSER, pollack are mainly found on both sides of the Norwegian Deeps, in
the Skagerrak and Kattegat, but (small) specimens are also regularly reported from inshore stations
along the continental coast. Incidental catches from the central North Sea often refer to foul hauls,
when the gear has been damaged by obstacles. Pollack are also frequently caught to the west of the
British Isles, in the Irish Sea and Celtic Sea and in the Channel. Incidental catches are recorded from
the Baltic Sea. No reports from Rockall or the Porcupine Bank area.
Depth distribution: The depth distribution covers the whole shelf area, while catches beyond a depth of
200 m appear negligible. Peak abundance varies between 8090 m in the CSER, 100125 m in the
NSER, and 4050 m in the BSER.
Depth distribution by ecoregion.
Size distribution: The LFD for the NSER shows two peaks: one around 35 cm, and a major one,
around 60 cm. For the CSER there is only one peak around 50 cm. The LFDs by depth band show
that pollack <40 cm are relatively more abundant in waters <50 m.
Length distributions: overall (left), and by depth band (right).
Time series: No clear signal is seen in the time series for the CSER and NSER, which may be caused
by their irregular appearance in trawl catches owing to a low catchability. Moreover, catches of pollack
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Pollachius
pollachius
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Pollachius
pollachius
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Pollachius
pollachius
0.0
0.5
1.0
0 25 50 75 100
length class (5 cm)
Pollachius
pollachius
E
F
L
0
2
4
6
8
0 15 30 45 60 75 90 105
lfd
length class (5 cm)
Pollachius
pollachius
<50 m
>50 m
43
often indicate gear damage and over time gear damage has declined considerably because stations
have been largely restricted to ‘clean tows’ based on improved GPS locations.
Survey indices by ecoregion.
Biology
Biological information is scarce. Instead of being largely restricted to hard bottoms close to the shore
(Svetovidov, 1986), the surveys show that the main distribution area is well offshore. While juveniles
appear to have a strong preference for coastal habitats, adults are often associated with wrecks and
other obstacles (Quéro and Vayne, 1997). The maximum age observed is 15 years, but firm data on
growth rates are lacking. In the CSER, pollack mature at about 3 years of age (ICES, 2012b). In
northwest Spain, L50% is 36 and 47 cm for males and females, respectively (Alonso-Fernández et al.,
2013). When held in captivity under natural light and temperature conditions, maturity was reached by
males after 2 years and by females after 3 years (Omnes et al., 2002). Experiments carried out at 8°C
indicate a fecundity of about 600 eggs per g body weight (Suquet et al., 2005). The eggs are 1.10
1.22 mm in diameter, the yolk is unsegmented and there is no oil globule (Russell, 1976). Young
pollack exhibit strong schooling behaviour, similar to young saithe, and move gradually away from the
coast as they grow (ICES, 2012b). The diet comprises mainly fish, but incidentally crustaceans and
cephalopods may also be eaten (Bergstad, 1991; ICES, 2012b). Using DNA techniques, some genetic
differentiation has been found, but sample sizes were small (Charrier et al., 2006). Both surveys and
fisheries indicate that the pollack west of the British Isles and in the English Channel are well
separated from those in the northeastern North Sea and Skagerrak/Kattegat.
Exploitation
Pollack form spawning aggregations and these may be targeted by commercial fisheries (ICES,
2012b). Elsewhere, they only serve as a highly valued bycatch or as a target for recreational fisheries.
The potential use for aquaculture has also been considered (Suquet et al., 2005). An analysis of stock
development in the Skagerrak and Kattegat for the period 19062007, based on trawl surveys and
commercial catches, suggests that stock biomass increased from 1940 onwards to reach a peak in the
late 1950s. Since then the biomass has declined to reach an all-time low around 2000, which might be
linked to an increase in sea temperatures (Cardinale et al., 2012).
0
1
2
3
4
5
6
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Pollachius pollachius
0
1
2
3
4
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Pollachius pollachius
44
32.7 Saithe Pollachius virens
(Linnaeus, 1758)
DE: Köhler, Seelachs; ES: Carbonero; FR: Lieu
noir; NL: Zwarte koolvis; NO: Sei
Lmax: 130 cm (Wheeler, 1978)
Data range: size 8126 cm; depth 1634 m
Catch rates of saithe.
General
What is in a name? Saithe sounds fine, but vernacular names referring to their colour (coalfish, coley)
would not help selling. In Dutch, the common name is a superlative, “zwarte koolvis” (black coalfish).
Consequently, the market prices were always lower than those of its congener, the ‘white coalfish’
(pollack), which gets the same price as cod. Because Seelachs sounds a lot better, the prices across
the German border were also better and in the 1980s Dutch fishers started to land their saithe in
Bremerhaven, before returning to their home port to sell the rest.
Taxonomy and identification: Saithe has three dorsal and two anal fins. The anal fin is long, with its
origin under the space between the first and second dorsal fin. The interspaces between the dorsal
and anal fins are relatively long. The most obvious characteristics to distinguish saithe from pollack are
that the lateral line is light against a dark-green body and straight, and that the jaws are of equal size.
Biogeographical distribution: Saithe is a boreal species distributed in the western Atlantic from North
Carolina to southwest Greenland, and in the eastern Atlantic from the Bay of Biscay to Iceland,
Spitsbergen and the Barents Sea (Svetovidov, 1986). The size of the American population (where it is
known as Atlantic pollock) is much smaller than the European.
Survey data
Spatial distribution: The distribution of saithe in the Atlas area highlights their concentration in the
northern part of the North Sea, Skagerrak, along the shelf edge north and west of Scotland and
Ireland, Rockall and in the area of Porcupine Bank. It is largely absent from the Celtic Sea, Irish Sea,
Channel, southern North Sea and the Baltic Sea (except for the most western part). However
incidental catches may occur everywhere. This might be related to the habit of juveniles to spread
along the coast in very shallow waters. Juveniles have for instance regularly been reported in fyke
45
catches within the harbour of IJmuiden, far away from the nearest spawning area. When they grow
larger, they might want to find their conspecifics and this could cause the occasional reports
throughout the shelf area.
Depth distribution: Saithe were most abundant at depths between 125 and 250 m. However, being a
semi-pelagic species the main distribution may well extend over deeper water beyond the shelf edge,
where only the fraction that is present in the bottom layer can be sampled by demersal trawls. Also the
presence of juveniles in shallow waters is underestimated. Only in the BSER, are saithe predominantly
found at <50 m depth.
Depth distribution by ecoregion.
Size distribution: The LFDs peak at 4050 cm in both the CSER and the NSER, which corresponds to
24 year old fish. In contrast, the peak in the BSER lies around 25 cm (1-year-olds), which
corresponds to the much shallower depth distribution. Younger age groups are mostly found in coastal
areas, while the distribution of mature saithe is not adequately covered by the surveys. Only in the
CSER, a small peak of large saithe is visible (75100 cm).
Length distributions: by ecoregion (left), and by depth band (right).
Time series: The time series for the CSER shows a sharp initial decline, followed by a period in which
abundance remained mostly below the long-term mean (=1). During the last 10 years, abundance
fluctuates around the mean. The NSER is characterized by large fluctuations, but over the entire
period there appears to have been a slight increase, with a positive outlier in the very last year. In the
BSER, saithe turn up only occasionally in any numbers.
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Pollachius virens
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Pollachius virens
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Pollachius virens
0.0
0.1
0.2
0.3
0 25 50 75 100 125
lfd
length class (5 cm)
Pollachius virens
E
F
F
0
1
2
3
4
5
6
7
0 25 50 75 100 125
lfd
length class (5 cm)
Pollachius
virens
<50 m
>50 m
46
Survey indices by ecoregion.
Biology
Habitat: Saithe live a semi-pelagic life in shoals that may be encountered over broad depth ranges,
from over the shelf edge to close-inshore areas depending on size and age, and near the bottom as
well as in midwater, or even near the surface. The adults sometimes make extensive diel vertical
migrations and may be found hundreds of metres above the bottom at night, as well as close to the
bottom during the day, at depths of >300 m (Bergstad, 1991). The shoals may also move off the shelf
and stay off the bottom continuously. In contrast, the 0- and 1-group saithe occur almost exclusively in
inshore waters (fjords and harbours). Overall, habitat characteristics are wide ranging and depend on
life-history stage.
Age, growth and maturity: Males and females have similar growth rates during the first 6 years of life,
but females become ultimately slightly larger. However, the survey data may overestimate the mean
length of the younger age groups, if only the larger specimens within an age class recruit to the
offshore stock that is being sampled adequately. The majority has reached maturity at age 6. Partial
recruitment of only the larger fish within a year class might explain the irregular maturation pattern
seen in the younger age groups.
Mean length (left) and percentage maturity (right) by age group of North Sea saithe (data Q1 IBTS, 20002004).
Reproduction: Spawning takes place from January (in southern areas) to May (further north), and
generally occurs along the edge of the continental shelf (Reinsch, 1976). There is no evidence of
spawning in the Skagerrak/Kattegat. A 75 cm long female produces, on average, 3 million eggs during
a spawning season, equivalent to 750 eggs per g body weight (Storozhuk and Golovanov, 1976).
Early stages: The eggs are 1.031.22 mm in diameter, the yolk is unsegmented and there is no oil
globule (Russell, 1976). The pelagic larvae and post-larvae are transported by the currents along the
shelf edge. In the North Sea, 0-group saithe can be found pelagically in the open northern part in
June, from where they move to shallow habitats (lochs and fjords) along the Scottish and Norwegian
coasts. Not infrequently they spread out to reach the outer harbours in south Scotland. On the
Norwegian coast, juveniles (46 cm) are usually first seen in shallow water in late April or beginning of
May. Tagging experiments have shown that young saithe leave their coastal nurseries during spring
and shift towards deeper water close to the coast during the next two years of life (Nedreaas, 1987)
before joining the offshore component of the stock (Newton, 1984).
0
1
2
3
4
5
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Pollachius virens
0
1
2
3
4
5
6
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Pollachius virens
0
2
4
6
8
10
12
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Pollachius virens
0
10
20
30
40
50
60
70
1 2 3 4 5 6
Mean length (cm)
Age (year)
F
M
0
20
40
60
80
100
1 2 3 4 5 6
Percentage maturity
Age (year)
F
M
47
Movements and migrations: Both fisheries and tagging experiments provide evidence of seasonal
spawning migrations. Saithe usually aggregate in schools that comprise fish of similar size.
Occasionally, long-distance journeys are undertaken based on tag returns from northern Norway,
Iceland and Faroe Islands (Homrum et al., 2013; Jakobsen and Olsen, 1987). However, extensive
tagging experiments of juveniles on the Norwegian west coast in the 1970s showed that around 90%
of the tag returns came from the northern North Sea (Jakobsen, 1978). Recaptures of saithe tagged
on the Scottish east coast were also mainly from the northern North Sea, where they apparently mix
with Norwegian recruits (Newton, 1984). Tagging in the Clyde area gave mainly local recaptures. IBTS
data have shown that density in the northeastern North Sea is markedly higher during summer than
during winter, suggesting dispersal during the feeding season (Knijn et al., 1993).
Trophic ecology: Young saithe in inshore waters feed on planktonic organisms, including copepods
and euphausiids, but are able to change to a benthic diet when suitable planktonic prey is scarce, or
feed on larval and juvenile fish (Nedreaas, 1987). Adults feed almost entirely on pelagic and demersal
fish, such as herring, Norway pout, haddock and sandeel, though euphausiids and other invertebrates
are also consumed (Du Buit, 1991; Hislop, 1997). See also Box on p. ###. Juveniles are occasionally
eaten by larger gadoids and other demersal fishes and are also part of the diet of harbour seals (Tollitt
et al., 1998).
Diseases and parasites: An epizootic of the bacterial infection vibriosis occurred in young saithe on the
Norwegian coast in 1974, which caused skin lesions and according to fishermen strange schooling
behaviour, and ultimately mass mortality. Similar outbreaks appear to have been common in previous
years (Egidius and Andersen, 1975).
Stock structure: Saithe in the North Sea, Skagerrak/Kattegat and West of Scotland are considered to
represent one unit stock, although some exchange with saithe from the Faroes and the Northeast
Arctic may be expected (Homrum et al., 2013).
Exploitation
In many European countries, saithe is an important species for human consumption. A directed fishery
is executed along the shelf edge by Norwegian, German and French offshore trawlers. In Norway,
there is also a directed gillnet fishery for adult saithe in the northern North Sea and a purse seine
fishery for immature fish in coastal areas. Because of the spatial separation among size classes,
discards in targeted saithe fisheries are generally low. Annual landings in the North Sea and to the
west of Scotland peaked at 300 thousand t in the mid-1970s. Since then, landings have decreased to
a stable level of approximately 100 thousand t per year (ICES, 2013).
48
32.8 Norway pout Trisopterus esmarkii (Nilsson,
1855)
DE: Stintdorsch; ES: Faneca noruega; FR: Tacaud
norvégien; NL: Kever; NO: Øyepål
Lmax: 35 cm (Baranenkova and Khokhlina, 1968)
Data range: size 233 cm; depth 41105 m
Catch rates of Norway pout.
General
Norway pout is a short-lived, boreal species, living in deeper waters on the outer shelf as well as
along and beyond the shelf edge. It has a bentho-pelagic life style, living in extensive shoals near the
bottom during the day and dispersing in midwater during the night. One can easily get bored sorting
through piles of Norway pout on a research vessel in the northern North Sea. However, when viewed
alive under natural conditions, one would hardly recognize the beautifully coloured creature with dark
bands on its body and iridescent fins from the dull fish on a measuring board.
Taxonomy and identification: Norway pout is distinguished from its congeners (T. minutus and T.
luscus) by having a lower jaw that protrudes slightly beyond the upper jaw, and by having a relatively
short and thin barbel. There is a small dusky spot on the upper edge of the pectoral fin base. The
dorsal surface is yellowish-brown, shading to silvery white beneath. A recent synonym is Gadus
esmarkii.
Biogeographical distribution: Distributed in the Northeast Atlantic only, from the Channel to Iceland
and extending along the Norwegian coast into the southwestern Barents Sea (Svetovidov, 1986).
Survey data
Spatial distribution: Norway pout have both a northern and a western distribution in the atlas area with
high concentrations running from the Skagerrak through the northern North Sea beyond the 100 m
depth contour, off the Scottish west coast, and around Ireland. Its southern limit cuts a sharp line
through the Kattegat, the central North Sea and the Celtic Sea, below which catches are marginal. It is
49
also absent from Rockall and catches in the Porcupine Bank area are much lower than on the
adjacent shelf.
Depth distribution: In the NSER and CSER, Norway pout was found mostly between 80 and 250 m
deep, on average slightly deeper in the former. The few fish venturing into the BSER have been
caught at much shallower depths.
Depth distribution by ecoregion.
Size distribution: Individuals of up to 33 cm were reported in trawl surveys. The LFDs by ecoregion did
not reveal marked differences, all showing a bimodal pattern with the first peak around 1011 cm and
the second peak around 1617 cm. The smallest individuals are found in shallower waters.
Length distributions: by ecoregion (left), and by depth band (right).
Time series: The long-term estimates of abundance show large fluctuations. In the CSER, Norway
pout were especially abundant in the mid-1990s and at the end of the time series. In the NSER,
abundance fluctuated annually, but there is also some periodicity: low in the 1980s, high in the 1990s
and low again after 2000, but increasing in recent years.
Survey indices by ecoregion.
Biology
Habitat: Mostly found in open, deeper water (>80 m), over muddy bottoms.
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Trisopterus
esmarkii
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Trisopterus
esmarkii
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Trisopterus
esmarkii
0.0
0.5
1.0
0 10 20 30 40
lfd
length class (2 cm)
Trisopterus
esmarkii
E
F
L
0
2
4
6
8
10
12
0 6 12 18 24 30 36
lfd
length class (2 cm)
Trisopterus
esmarkii
<50 m
>50 m
0
1
1
2
2
3
3
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Trisopterus esmarkii
0
1
2
3
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Trisopterus esmarkii
50
Age, growth and maturity (see also Table ###): Norway pout usually grow to a maximum length of
about 20 cm, and rarely as large as 25 cm. They seldom get older than 4 years. Females may grow to
a larger size than males, and females dominate numerically in the older age groups (Albert, 1994).
Norway pout mature partly as 1-year old and almost all are mature at 2-year old. The proportion of 1-
year-old reaching sexual maturity varies markedly from year to year and has been relatively high in
recent years (see Figure ###; Lambert et al., 2009).
Temporal variability in percentage mature Norway pout at age 1 and 2, 19832006 (After Lambert et al., 2009).
Reproduction: The spawning season in the North Sea lasts from January to March (Lambert et al.,
2009; Nash et al., 2012). Few observations of “running” or spent Norway pout are available for the
Skagerrak area (Lambert et al., 2009), indicating that no spawning takes place there. Concentrations
of eggs and larvae have also been found to the north and west of the Outer Hebrides (Schmidt, 1909;
Raitt, 1965). Mortality has been shown to increase markedly with age. Because other possible
explanations (such as a size-selective fishery, higher predation pressure on older individuals, and
size-related catchability in the survey gear) could be ruled out, it has been argued that a high
proportion of the fish must die after spawning (Sparholt et al., 2002; Nielsen et al., 2012). A female
produces 420980 eggs per g body weight, equivalent to 21 thousand eggs for a 30 g (2-year-old) fish
(Raitt, 1968).
Early stages: The pelagic eggs are small (1.001.28 mm), and do not contain an oil globule (Russell,
1976). Early larvae are mainly found in the northwestern North Sea (ICES, 2007), while larger larvae
occurred to the southeast of this area, suggesting advection of young stages to the southeast and
toward the Skagerrak (Nash et al., 2012). In the past, small numbers of larvae have been recorded in
the Celtic and Irish Seas (Schmidt, 1909), but no surveys have been carried out there since. After
metamorphosis, the 0-group fish are found in midwater in June (1.56.0 cm; Heessen et al., 1982; see
also Box on p. ###). There is no evidence of specific nursery areas.
Movements and migrations: During the summer, the 0-group, which inhabit initially only the layer
above the thermocline, start to migrate vertically in the water column, being found close to the seabed
during the daytime and spending the night in midwater (Bailey, 1975).
Trophic ecology: Pelagic 0-group Norway pout feed mainly on copepods and appendicularians (Robb
and Hislop, 1980). The diet of larger specimens (1020 cm) consists of crustaceans such as mysids,
natantids, copepods, euphausiids and amphipods, and of small fish, mainly gobies. Feeding tends to
be more intensive at night (Raitt and Adams, 1965; Albert, 1994). Extensive stomach-sampling
programmes in 1981 and 1991 have shown that cod, whiting and saithe are major predators of
demersal Norway pout, while mackerel is the main predator on 0-group (Daan, 1989; Hislop, 1997).
Total mortality has decreased over the recent two decades, consistent with a substantial decline in the
0
20
40
60
80
100
1980 1990 2000 2010
Percentage mature
Year
age 1
age 2
51
stock sizes of the three main gadoid predators (Sparholt et al., 2002). Norway pout is also an
important prey for other demersal fishes and marine mammals.
Stock structure: Norway pout in the North Sea and Skagerrak/Kattegat area are supposed to belong to
one unit stock. Whether the west of Scotland and Celtic Sea populations belong to different stocks
remains unclear.
Exploitation
Because of its small size, Norway pout is of no use for human consumption, but because of the high
abundance an industrial fishery has developed for reduction to fishmeal and fish oil, especially by
Denmark and Norway. Because dense schools are usually found within a few metres of the seabed,
the industrial fishery is to a large extent carried out with bottom trawls. The high bycatch of other
commercial fish species (especially haddock and whiting) in the northwestern North Sea has led to the
introduction of the so-called “Norway pout box” several decades ago, where it is forbidden to fish for
Norway pout (Nielsen and Mathiesen, 2006). Annual landings rose from almost nil in the 1960s to over
750 thousand t in the mid-1970s, decreased again to a little more than 100 thousand t in the late
1980s, and have been irregular at a low level since the late 1990s (ICES, 2012d). There is no fishery
in the CSER.
52
32.9 Bib Trisopterus luscus (Linnaeus,
1758)
DE: Franzosendorsch; ES: Faneca; FR:
Grand tacaud; NL: Steenbolk; NO:
Skjeggtorsk
Lmax: 41 cm (Wheeler, 1978)
Data range: size 249 cm; depth 0317 m
Catch rates of bib.
General
Bib is a medium-sized gadoid of minor commercial importance. It is sometimes called pout or pouting,
but these names can lead to confusion with the congeneric T. minutus. Divers regularly spot this
species near wrecks and obstacles.
Taxonomy and identification: Bib has three dorsal and two anal fins. The anal fin is long, with its origin
under the first dorsal fin. Interspaces between the dorsal and anal fins are virtually absent: indeed,
pulling the first anal fin forward will draw the second anal fin with it (not so in T. minutus). The body is
deeper than in T. minutus and the chin barbel is large. There is a dusky blotch at the base of the
pectoral fin. In live fish, four or five dark-coloured cross-bands are seen on the upper part of the body.
Genetic analyses suggest that T. luscus is closely related to T. minutus capelanus, the sub-species of
poor cod that is found in the Mediterranean Sea (Mattiangeli et al., 2000). An earlier synonym was
Gadus luscus.
Biogeographical distribution: A Northeast Atlantic species found in the Skagerrak, the North Sea,
around the British Isles, Bay of Biscay and south to Morocco and in the western Mediterranean Sea
(Svetovidov, 1986).
Survey data
Spatial distribution: Bib is most common in the English Channel, Southern Bight, Bristol Channel and
Irish Sea. Records from the Skagerrak and western Baltic Sea are few. The distribution in the North
Sea appears to follow closely the 50 m depth contour.
53
Depth distribution: A shallow water species that is most abundant in waters less than 50 m deep, but
extending into somewhat deeper waters in the CSER (mostly <80 m).
Depth distribution by ecoregion.
Size distribution: Specimens of up to 49 cm have been recorded, well above the reported Lmax (41 cm;
Wheeler, 1978). Most fish, however, were <20 cm, with a peak at 1016 cm. When the data are split
by depth band, two modes appear. Below 50 m, almost only small fish were taken, whereas in deeper
water, a clear peak emerges around 2426 cm.
Length distributions: by ecoregion (left), and by depth band (right).
These differences in distribution between juveniles and older bib become clearly visible on a spatial
scale. While the main concentrations of small bib are restricted to the eastern Channel, Southern
Bight, Bristol Channel and Irish Sea, large bib are also numerous in the western Channel. Furthermore
they roam much further into the North Sea reaching Scottish waters and the Skagerrak.
Catch rates of small (<16 cm; left) and larger (>=16 cm; right) bib.
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Trisopterus luscus
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Trisopterus luscus
0.0
0.5
1.0
0 10 20 30 40
lfd
length class (2 cm)
Trisopterus luscus
E
F
L
0
1
2
3
4
5
6
7
0 6 12 18 24 30 36 42 48
lfd
length class (2 cm)
Trisopterus luscus
<50 m
>50 m
54
Time series: Apart from a peak in the CSER in 1988, abundance gradually increased up to the early
2000s, but has markedly declined since. In the NSER, the pattern is quite irregular but indicates a
general long-term decline.
Survey indices by ecoregion.
Biology
Habitat: Large bib may form schools on rocky grounds, around reefs and also associate with obstacles
such as ship wrecks (Zintzen et al., 2006). Smaller individuals may also be found on sandy inshore
sediments. The maps seem to suggest that bib favour areas with strong tidal currents such as the
Channel.
Age, growth and maturity (see also Table ###): Bib is a fast growing, relatively short-lived species. In
the NSER, juveniles of 23 cm are found in May (Desmarchelier, 1985). They attain 18 cm during the
first quarter of their second year of life, a length of 27 cm during their third year, and 32 cm during their
fourth year. Females grow to a somewhat larger size than males (Korf, 1971). In the Channel, the
maximum age was 5 years for females and 7 for males (Desmarchelier, 1985). Both sexes mature at
an age of 2 (Korf, 1971; Desmarchelier, 1985). In Galician waters, L50% for males was 20 cm and for
females 18 cm (Labarta and Ferreiro, 1982), but these values could be influenced by the methods
used (Alonso-Fernández et al., 2008).
Reproduction: Postlarvae have been found in every month of the year (Russell, 1976) but peak
spawning varies with latitude. The spawning period in the southern North Sea is rather protracted,
from February to August (Korf, 1971). In north Spanish waters, spawning occurs from December to
April, with small fish spawning later than larger specimens (Merayo, 1996). In Galician waters,
spawning has been observed throughout all months. Fish in the length range of 1940 cm spawned
on average 20 batches, consisting of 50 to 57 thousand eggs. Fecundity ranged from 20 to 1327
thousand oocytes per female (Alonso-Fernández et al., 2008).
Early stages: The pelagic eggs are spherical without an oil globule and have a diameter of 0.91.23
mm (Russell, 1976). The larvae arrive, transported passively by tidal currents, in early to mid-June in
bays and estuaries, where they build up high densities close inshore and adopt a demersal life style
after metamorphosis. With increasing size, they move into deeper water (Korf, 1971; Cohen et al.,
1990).
Movements and migrations: Fowler et al. (1999) found that juvenile bib formed small, non-feeding
schools near artificial reefs during daytime, which they left some 1530 min after dusk to return 4560
min before dawn.
Trophic ecology: Small bib prey on shrimps (especially pandalids and crangonids), mysids,
amphipods, crabs, polychaete worms, and fish (sandeel, dragonet, post-larval flatfish). About one
quarter of the diet of larger individuals consists of fish such as sprat, gobies and dragonets (van den
Broek, 1978; Armstrong, 1982; Hamerlynck and Hostens, 1993; Reubens et al., 2011).
Exploitation
0
1
2
3
4
5
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Trisopterus luscus
0
1
2
3
4
5
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Trisopterus luscus
55
Bib is of marginal economic interest in the Atlas area, although the larger sizes are nowadays being
landed for human consumption. Further south (France, Spain and Portugal), it is of local importance
for artisanal fleets (Alonso-Fernández et al., 2008).
56
32.10 Poor cod Trisopterus minutus
(Linnaeus, 1758)
DE: Zwergdorsch; ES: Capellán; FR: Petit
tacaud; NL: Dwergbolk; NO: Sypike
Lmax: 26 cm (Wheeler, 1978)
Data range: size 235 cm; depth 01105 m
Catch rates of poor cod.
General
Although a full-grown poor cod is easily distinguished from a full-grown bib, it is different with juveniles.
In that case, it is worthwhile to use the pull-the-anal-fin test (see below) to build up experience in
identification.
Taxonomy and identification: A small-bodied gadoid with three dorsal and two anal fins. The anal fin is
long, with its origin under the first dorsal fin. The interspaces between the dorsal and anal fins are
short, but the two anal fins are not continuous at the base (pulling the first anal fin forward does not
move the second one). They have a chin barbel, and the upper jaw is longer than the lower one. At
the base of the pectoral fin there is a dusky blotch, but less pronounced than in T. luscus. The body is
coppery coloured and the fins are not as dark as in T. luscus. Two subspecies have been
distinguished: T. minutus minutus in the Atlantic, and T. minutus capelanus in the Mediterranean
(Svetovidov, 1986). Known previously also as Gadus minutus.
Biogeographical distribution: From mid-Norway, around the British Isles, in the North Sea, Skagerrak
and Kattegat, south to Morocco and in the western Mediterranean Sea (Svetovidov, 1986).
Survey data
Spatial distribution: Poor cod is one of the most widely distributed species in the Atlas area, except for
the Baltic Sea where only incidental catches have been reported in the western part. However,
densities in the CSER were mostly a factor 100 higher than anywhere in the North Sea, with the
exception of the eastern Channel and waters of the north coast of Scotland. Within the North Sea,
densities were higher all along the British east coast than in more easterly waters, except for a small
57
band running along the edge of the Norwegian Deeps into the Skagerrak/Kattegat, leaving an almost
empty space in the central northern North Sea.
Depth distribution: The depth distribution differed markedly between the CSER, where the highest
densities were reported beyond 70 m depth, and the NSER, where these occurred between 20 and 60
m. In the BSER, the two peaks refer to low numbers only.
Depth distribution by ecoregion.
Size distribution: The majority of the poor cod caught were <24 cm. However, the maximum length of
35 cm reported exceeds the maximum of 26 cm given by Wheeler (1978) considerably. The LFD for
the CSER shows two peaks, one around 812 cm representing 0-group fish and one around 17 cm.
The second one is absent in the NSER and more strongly present in the BSER. The split by depth
band shows that the 0-group dominated the distribution at depths <50 m, while the larger ones were
virtually restricted to deeper waters.
Length distributions: by ecoregion (left), and by depth band (right).
Time series: In the CSER, abundance has on average increased since the start of the surveys, while
In the NSER abundance has followed an almost exponential decline since the beginning. The catches
in the BSER are too low for a meaningful time series.
Survey indices by ecoregion.
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Trisopterus
minutus
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Trisopterus
minutus
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Trisopterus
minutus
0.0
0.5
1.0
010 20 30 40
lfd
length class (2 cm)
Trisopterus
minutus
E
F
L
0
2
4
6
8
10
0 6 12 18 24 30 36
lfd
length class (2 cm)
Trisopterus
minutus
<50 m
>50 m
0
2
4
6
8
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Trisopterus minutus
0
5
10
15
20
25
30
35
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Trisopterus minutus
58
These two opposite changes are visualized by comparing the distribution in three periods. The pattern
is remarkably similar to whiting.
Biology
T. minutus aggregates in schools near the bottom and in mid-water within a depth range of 25300 m
(Wheeler, 1978), but less close inshore and less associated with rough grounds than T. luscus. On the
eastern slope of the Norwegian Deeps, they are most common at depths between 60140 m
(Bergstad et al., 1991). Estimates of the average length of 1- and 2-year-old poor cod in the southern
North Sea in February are 12 and 17 cm, respectively (Korf, 1971; Devidas Menon, 1950). Ages read
from fish in the 1325 cm length range from western Norway varied from 1 to 8 years (Albert, 1993).
Maturity may be reached at 2-year old (Korf, 1971). Spawning off Plymouth occurs during February
May, peaking in March and April (Devidas Menon, 1950). The pelagic, spherical eggs have a diameter
of 0.951.03 mm and no oil globule (Russell, 1976). Underwater observations at Orkney indicate that
0-group poor cod can be locally abundant in shallow water (J.R.G. Hislop pers. comm.). Stomach
content investigations indicate that poor cod are opportunistic and flexible predators, feeding on swift
suprabenthic prey (mysids, euphausiids and shrimps), benthic polychaetes and crustaceans (young
decapods), as well as small demersal fish species (young dragonets), the actual composition
depending on size and location (Devidas Menon, 1950; Korf, 1971; Armstrong, 1982; Mattson, 1990;
Albert, 1993).
Exploitation
While constituting a small bycatch in the industrial fisheries, poor cod are of no economic importance
and commonly discarded in human consumption fisheries.
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Average n/hour
0 to 0.0001
0.0001 to 0.1
0.1 to 1
1 to 10
10 to 100
100 to 1000
1000 to 10000
10000 to 1000000
Trisopterus minutus
1977-1989
-14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18 20 22 24
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Average n/hour
0 to 0.0001
0.0001 to 0.1
0.1 to 1
1 to 10
10 to 100
100 to 1000
1000 to 10000
10000 to 1000000
Trisopterus minutus
1990-1999
-14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18 20 22 24
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Average n/hour
0 to 0.0001
0.0001 to 0.1
0.1 to 1
1 to 10
10 to 100
100 to 1000
1000 to 10000
10000 to 1000000
Trisopterus minutus
2000-2013
59
32.11 Tadpole fish Raniceps raninus
(Linnaeus, 1758)
DE: Froschdorsch; ES: Ranúnculo negro;
FR: Grenouille de mer; NL: Vorskwab;
NO: Paddetorsk
Lmax: 30 cm (Wheeler, 1978)
Data range: size 325 cm; depth 16528 m
Presence/absence of tadpole fish
Summary
The tadpole fish also known as lesser fork-beard appears to live a solitary life on rocky bottoms.
As the name says, it looks a bit like a large tadpole with a broad head and a small barbel on its chin. It
has two dorsal fins (the first very small and with three fin rays, the second long) and one anal fin, all
with light edges. The overall dark colour has been described as leaden brown to liver, whilst mouth
and lips are white (Wheeler (1978). It is distributed in the Northeast Atlantic from Trondheim to the Bay
of Biscay, including Skagerrak, Kattegat and (rarely) the western Baltic Sea (Svetovidov, 1986). Some
taxonomists have considered this species to represent a mono-specific family (Ranicepteridae).
Depth distribution by ecoregion: CSER (left), and NSER (middle). Overall length distribution (right).
The sporadic survey records lie scattered over much of the area (except for the Porcupine Bank,
Rockall or Baltic Sea) and mostly refer to individual specimens mostly in the 614 cm size range).
They have been recorded close to land, but also far offshore. Most observations were in waters <200
m deep. Catches are too few to be indicative of abundance trends. Although former observations often
refer to shallow waters (depths of 1015 m) among algae-covered rocks as well as over sandy and
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49
50
51
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61
62
Raniceps raninus
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Raniceps raninus
0.0
0.5
1.0
0 5 10 15 20 25
lfd
length class (cm)
Raniceps raninus
60
muddy bottoms (Wheeler, 1978; Svetovidov, 1986) , the habitat apparently extends to much larger
depths. Tadpole fish may better be viewed as elusive rather than rare. The pelagic, spherical eggs
(0.750.91 mm in diameter, with a characteristic pigmentation and an oil globule 0.140.19 mm in
diameter) have been observed from mid-May to the beginning of September, the postlarvae from July
to October. From a size of 12 mm onwards “a trace of the barbel can be seen and the young fish is
now assuming its adult characters (Russell, 1976). The demersal stage starts from a length of about 2
cm (Wheeler, 1978). A large female of 31 cm (508 g) caught in 2010 in Dutch waters was estimated as
being 8 years old. The food consists mainly of shrimps and sometimes of small fishes and worms
(Wheeler, 1978). The species is an infrequent bycatch in inshore trawl and pot fisheries, but has no
commercial value.
61
Family Gadidae (Subfamily Lotinae) Rocklings
The subfamily of the Lotinae comprises six genera and about 23 species. All are characterised by an
elongated shape and the presence of a chin barbel. They have 13 dorsal fins and always one anal
fin. Eight species have been reported more or less reliably in the surveys, but the data for members of
the genus Gaidropsarus have been combined in a single section because of apparent mis-
identifications. All species are discussed below, except for burbot Lota lota, which has been reported
in the Baltic Sea surveys, but represents the only typical freshwater species.
Postlarva of Enchelyopus cimbrius (10.2 mm). From Demir et al. (1985).
The rocklings of the genera Ciliata, Enchelyopus and Gaidropsarus are characterized by a specific
post-larval stage called ‘mackerel midges’. The larvae metamorphose to small fish with a greenish
blue-back, silvery sides and belly, and long fins. These may be found in considerable numbers in the
neuston the biota inhabiting the top layer of the water column close to the surface during autumn
(Nellen and Hempel, 1970; Hislop, 1979; Tully and Ó Céidigh, 1989a). They are sometimes so
numerous that they may form an important part of the diet of nestlings of terns and puffins (Wheeler,
1978). Although having small barbels, they do not resemble the older fish and their identification to the
species level remains difficult. However, because of their life style, mackerel midges do not show up in
bottom trawl catches.
Adult rocklings are primarily distinguished by the number of barbels, but this feature can easily lead to
confusion in juvenile fish. Inconsistencies in reporting among countries and even within countries
among years are widespread. To the extent possible, obvious mis-identifications have been corrected.
32.12 Tusk Brosme brosme (Ascanius, 1772)
DE: Lumb; ES: Brosmio ; FR: Brosme; NL: Lom; NO: Brosme
Lmax: 110 cm (Wheeler, 1978)
Data range: size 7103 cm; depth 16639 m
Presence/absence of tusk.
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Brosme brosme
62
General
Tusk also named torsk or cusk are solitary, boreal fish that live a sedentary life on rocky grounds
of the outer shelf, the upper continental slope and beyond. They are loved by anglers, because they
are strong fighters and taste good.
Taxonomy and identification: The genus is monospecific. B. brosme has uninterrupted dorsal and anal
fins, both narrowly joined to the caudal fin. The length of the single chin barbel equals the diameter of
the eye. The minute scales are deeply embedded in the skin and so the species appears to be
scaleless. Colour is variable but usually brownish-grey with paler belly. The fins are light with a black
and white margin (Svetovidov, 1986).
Biogeographical distribution: Tusk is distributed in the Northeast Atlantic from southern Ireland
northward to the western Barents Sea and Spitsbergen, including Iceland and the Faroe Islands, the
northern North Sea and Kattegat (Svetovidov, 1986). Along the Mid-Atlantic Ridge, the species
extends at least as far south as the Charlie-Gibbs Fracture Zone (approx. 52oN; Hareide and Garnes,
2001). Within the northwestern Atlantic, its distribution extends from Greenland along the coasts of
Canada and the USA as far south as New Jersey (Cohen et al., 1990).
Survey data
Spatial distribution: Catches are largely restricted to waters beyond the 100 m depth contour in the
northern North Sea and along the shelf edge west of Scotland, south to the Porcupine Bank area,
including Rockall. There are no records from the Celtic Sea, although tusk has been caught
occasionally along the western seaboard of the British Isles (Quigley et al., 1992).
Depth distribution: Because of scarcity of records, data from NSER and CSER have been combined
(no records from the BSER). Density reaches a maximum on the outer shelf, tailing of in deeper water.
Overall depth distribution (left), and length distributions: overall (middle), and by depth band (right).
Size distribution: The overall length distribution shows two peaks around 25 and 60 cm Large tusk are
restricted to deeper waters (>200 m).
Time series: Catch rates are low and varied without trend during most of the survey period in both
ecoregions. Although catch rates in the North Sea have dropped markedly below the long-term
average in recent years, the data may not reflect trends in abundance accurately because of their low
catchability in survey gears.
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Brosme brosme
0.0
0.5
1.0
015 30 45 60 75 90 105
lfd
length class (5 cm)
Brosme brosme
0
2
4
6
0 15 30 45 60 75 90 105
lfd
length class (5 cm)
Brosme brosme
<200 m
>200 m
63
Survey indices by ecoregion.
Biology
Habitat: Tusk typically inhabit rocky grounds in deep water, where it is difficult to trawl. The overall
depth range reported in the literature is from 20 to 1100 m (Haedrich and Merrett, 1988; Cohen et al.,
1990; Moore et al., 2003).
Age, growth and maturity: Size- and weight-at-age data are available for various regions, which
confirm that growth is relatively slow. However, the precision of ageing by counting annuli in otoliths
tends to be low, especially in large fish (Magnússon et al., 1997; Bergstad et al., 1998). Tusk may
become at least 20 years old, but recent commercial longline catches comprise mainly 715 year old
fish. A50% is 67 years (corresponding to an L50% of around 40 cm), and females become mature
perhaps one year earlier than males (Joenoes, 1961; Bergstad and Hareide, 1996; Magnússon et al.,
1997).
Reproduction: The spawning season lasts from April to July. Data on egg distribution indicate that
spawning takes place over the entire geographical range but primarily in shelf waters down to 400 m
(Svetovidov, 1986; Bergstad and Hareide, 1996). Tusk eggs have been reported from the
northeastern North Sea and Skagerrak, south of the Shetlands, north and west of the British Isles, and
from Sognefjord (approx. 61°N) to the Lofoten (Ehrenbaum, 1909; Schmidt, 1909; Dannevig, 1945;
Wiborg, 1960). Bjørke (1981) recorded their occurrence along the Norwegian coast in the depth range
of 060 m. Tusk is a highly fecund species with females of 60 cm capable of spawning >1 million eggs
in a season (Oldham, 1972).
Early stages: The eggs are spherical (1.291.51 mm in diameter) with unsegmented yolk and a single
oil globule (0.230.30 mm) with a pinkish hue (Russell, 1976). Larvae and juveniles are mostly absent
from all but the northernmost areas of the North Sea, but otherwise widespread from the Hebrides and
Rockall, the Shetlands and Faroes to Iceland (Schmidt, 1905, 1909). The duration of the pelagic larval
and juvenile phase is not exactly known but presumably in the order of 14 months. Demersal
juveniles occur over the entire range of the species.
Trophic ecology: Tusk feed mainly on benthic megafauna such as molluscs and large crustaceans
(e.g. squat lobsters and Nephrops), but large specimens are also piscivorous, preying on a variety of
species including hagfish and blue whiting (Langton and Bowman, 1980; Svetovidov, 1986; Bergstad,
1991).
Stock structure: Early studies of enzyme systems indicated that tusk in the northeastern and
northwestern Atlantic belonged to different gene pools (Johansen and Nævdal, 1995), but were
inconclusive with regards to heterogeneity within its extensive northeastern range. Recent
microsatellite DNA analyses revealed weak, but significant, heterogeneity within this area, and
suggest that tusk associated with isolated banks such as Rockall Bank or separated by deep troughs
may form relatively isolated units (Knutsen et al., 2009). Although the stock structure remains
somewhat unclear, different management units are distinguished (e.g. Barents and Norwegian Sea,
Rockall Bank).
Exploitation
0
1
2
3
4
5
6
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Brosme brosme
0
1
2
3
4
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Brosme brosme
IBT
64
Tusk is a valued resource but mainly a bycatch in fisheries targeting other species. It is a secondary
target species of longline fisheries for ling (Bergstad and Hareide, 1996). Annual landings increased in
the early 1900s and stabilised at around 10 thousand t or less around 1950 (Joenoes, 1961). Since
then, landings increased steadily for a couple of decades, paralleled by increasing ling landings,
followed by a decline in recent years. Catch-per-unit-of-effort (cpue) data from Norwegian longliners
indicate a general decline in abundance from the early 1970s onwards until the 1990s (Magnússon et
al., 1997; Bergstad and Hareide, 1996). Although the decline in cpue seems to have halted or even
been reversed in some areas (ICES, 2012a), assessments are regarded as uncertain. There is also
concern about the status of tusk in the Northwest Atlantic, both in terms of over-fishing and of the
potential impact of climate change (Hare et al., 2012).
65
32.13 Five-bearded rockling Ciliata mustela
(Linnaeus, 1758)
DE: Fünfbärtelige Seequappe; ES: Mollareta; FR:
Motelle à cinq barbillons; NL: Vijfdradige meun; NO:
Femtrådet tangbrosme
Lmax: 25 cm (Wheeler, 1978)
Data range: size 327 cm; depth 0200 m
Catch rates of five-bearded rockling.
General
The five-bearded rockling is the most common rockling in inshore areas of the North Sea, but in
offshore areas confounding with northern rockling, its closest relative, is possible (Borges et al., 2010).
Even confusion with the rocklings of the genus Gaidropsarus cannot be excluded. The available data
show marked differences in depth distribution and length distribution between the CSER and the
NSER, which could be caused by major mis-identifications in one region or the other. Therefore, a
health warning in using the information presented is appropriate.
Taxonomy and identification: A gadoid with a small head, two dorsal fins (the first a single long ray
followed by a fringe of low rays, the second one long) and one anal fin. Five barbels: 1 on the chin, 1
on each anterior nostril, and 2 on the upper lip. No supplementary barbels as in C. septentrionalis.
Dark, green-brown in colour. The names Onos mustelus and O. mustela have also been used.
Biogeographical distribution: The distribution is restricted to the Northeast Atlantic, from Portugal to
northern Norway and Iceland, also in the Kattegat (Svetovidov, 1986).
Survey data
Spatial distribution: Five-bearded rockling are most abundant in the shallow southeastern North Sea
(specifically in the Waddensea), and in the southwestern North Sea near the Wash. They are also
found along the coasts of the western English Channel, the Bristol Channel and the Irish Sea. More
scattered, observations are reported from the Skagerrak and Kattegat, but not from the Baltic Sea.
66
Depth distribution: Five-bearded rockling is a typical shallow-water species that is found mainly in
waters <20 m deep in the NSER, but reports in the CSER cover a much larger depth range. The
sporadic reports in the CSER from outer-shelf waters (>100 m deep) and even slope waters can not
be validated and may well be erroneous.
Depth distribution by ecoregion.
Length distribution by ecoregion.
Size distribution: The LFDs of the catches reported by ecoregion show large discrepancies. While the
NSER is characterized by a single mode in the 1015 cm range, this size group represents a deep
trough in the CSER, where both smaller fish (510 cm) and larger fish (1520 cm) are much more
abundant. Given the remarkable differences in both the length distribution and depth distribution
between the two ecoregions, species identification should be checked carefully.
Time series: Given the uncertainty in species identification, the time series for the two ecoregions are
presented for what they are worth.
Survey indices by ecoregion.
Biology
Habitat: This littoral and sublittoral rockling is common in intertidal parts of rocky and sandy shores,
with larger specimens frequent on inshore muddy, sandy and shell gravel grounds (Wheeler, 1969).
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Ciliata mustela
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Ciliata mustela
0.0
0.5
1.0
0 5 10 15 20 25 30
lfd
length class (cm)
Ciliata mustela
0
1
2
3
4
5
6
7
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Ciliata mustela
0
1
2
3
4
5
1977 1982 1987 1992 1997 2002 2007 2012
abundance index
Ciliata mustela
67
Age, growth and maturity (see also Table ###): Five-bearded rocklings from a cooling water intake of
power stations in the Severn Estuary (Bristol Channel) measured on average 13, 18 and 23 cm at the
end of their first, second and third year, respectively, older fish being absent (Badsha and Sainsbury,
1978). Catches from the Dutch Waddensea consisted of five age-groups, most fish being 2-years-old.
The lengths observed for 0- to 4-group fish were: 13, 16, 19, 21 and 24 cm (Śmietana, 1992). Sexually
mature females have been observed from a length of 14 cm onwards (Badsha and Sainsbury, 1978).
Reproduction: In the Bristol Channel, the species is assumed to spawn from March to June. Fecundity
may vary considerably from 314 thousand oocytes for a 14 cm female (Badsha and Sainsbury,
1978).
Early stages: Eggs are pelagic, spherical (diameter 0.660.98 mm) and contain a single oil globule
(diameter 0.110.16 mm). The length of newly hatched larvae is 2.1 to 2.2 mm (Russell, 1976).
Pelagic juveniles (the ‘mackerel midges’) are found from spring to summer in the upper 10 cm of the
water column, off Plymouth from early April until late September (most abundant in June; Demir et al.,
1985), and in Galway Bay from March to August (Tully and Ó Céidigh, 1989a). It is not exactly known
at what size the juveniles adopt their demersal way of live, but the smallest size reported in demersal
trawl surveys was 3 cm.
Movements and migrations: Five-bearded rockling is a resident of the shallow Waddensea, but leaves
the area during winter to spawn (Zijlstra, 1978). In the Severn Estuary, they visit the middle reaches
during the autumn and winter months, and at the approach of sexual maturity, they leave in January to
spawn in deeper water (Badsha and Sainsbury, 1978).
Trophic ecology: Juveniles feed only during daylight hours on copepods, copepod eggs, and fish eggs
(Tully and Ó Céidigh, 1989b). Adult specimens from the Severn Estuary prey on a wide range of
organisms, but crustaceans (brown shrimp, gammarids, mysids, isopods) and gobies are generally of
major importance (Badsha and Sainsbury, 1978; Wheeler, 1978).
Exploitation
No economic value.
68
32.14 Northern rockling Ciliata septentrionalis
(Collett, 1875)
DE: Nördliche Seequappe; ES: ; FR: Motelle
nordique; NL: Noorse meun; NO: Nordlig tangbrosme
Lmax: 18 cm (Wheeler, 1978)
Data range: size 418 cm; depth 13517 m
Presence/absence of northern rockling.
General
A small, offshore rockling that has not been recorded in British waters until 1960 (Wheeler, 1969), and
that in the past has undoubtedly been overlooked by some countries participating in the surveys and,
may not always have been correctly identified even in recent years (Borges et al., 2010). Confounding
with both the five-bearded and juvenile three-bearded rockling seems likely. Therefore, its range in the
Atlas area could well be larger than indicated by the data. On the other hand, isolated records might
not be trusted.
Taxonomy and identification: The northern rockling has a relatively large head (compared to C.
mustela), two dorsal fins (the first one short, the second one long) and one anal fin. Like C. mustela,
they have five barbels (1 on the chin, 1 on each anterior nostril, 2 on the upper lip), but in addition
there are small supplementary lobes on the skin fold above the upper jaw (clearly visible under low
magnification when immersed in water). The two barbels on the upper lip are smaller than in C.
mustela, and can be easily missed. This may well have led to wrong identifications. The colour is
salmon pink. The name Onos septentrionalis has also been used.
Biogeographical distribution: Northern rockling is a boreal species that is distributed in the Northeast
Atlantic from the Channel area to northern Norway and Iceland (Svetovidov, 1986).
Survey data
Spatial distribution: The reported abundance is rather low and most records are concentrated in the
southwestern North Sea, the eastern English Channel, the Bristol Channel and the Irish Sea. Some
scattered catches have been reported from the northern North Sea and elsewhere, but not from
Skagerrak/Kattegat, nor from the Baltic Sea.
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Ciliata septentrionalis
69
Depth distribution: This rockling generally occurs in deeper waters than C. mustela. It has been mainly
reported from 10 to 125 m, the range perhaps being shifted to somewhat shallower depths in the
NSER compared to the CSER. The isolated records beyond 200 m may not be trusted until their
presence at these depths is properly documented.
Depth distribution by ecoregion.
Length distribution by ecoregion.
Size distribution: The LFDs in the two regions show a good deal of overlap, but the peak in the CSER
is at a smaller size (67 cm) than in the NSER (910 cm). In the latter, there is also a small bump
around 1314 cm.
Time series: The time series for the two ecoregions merely show the hap-hazard nature of the records
over time in both areas, suggesting an artefact of temporal differences in proper identification (Borges
et al., 2010).
Survey indices by ecoregion.
Summary
The main habitat lies below the tide mark, where northern rocklings feed on benthic organisms such
as decapod crustaceans, squat lobsters, porcellanid crabs, mysids, and polychaete worms (Wheeler,
1969). Pelagic juveniles have been observed off Plymouth between March and September in the
upper 10 cm of the water column (Demir et al., 1985). Additional information is available from a
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250
300
400
500
depth class
Ciliata
septentrionalis
0.0 0.5 1.0
0
5
10
15
20
30
40
50
60
70
80
90
100
125
150
200
250