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From: Martin A. Collins, Paul Brickle, Judith Brown, and Mark Belchier, The
Patagonian Toothfish: Biology, Ecology and Fishery.
In Michael Lesser editor: Advances in Marine Biology - 58, Burlington:
Academic Press, 2010, pp. 227-300. ISBN: 978-0-12-381015-1 © Copyright 2010
Elsevier Inc. Academic Press.
CHAPTER FOUR
The Patagonian Toothfish: Biology,
Ecology and Fishery
Martin A. Collins,*
,‡
Paul Brickle,
†,‡
Judith Brown,*
,†,‡
and
Mark Belchier
§
Contents
1. Introduction 229
2. Taxonomy and Systematics 230
3. Distribution and Life Cycle 232
3.1. Determining distribution and abundance 232
3.2. Geographic distribution 233
3.3. Life cycle and bathymetric distribution 234
3.4. Recruitment variability 236
4. Population Structure, Movements and Migration Patterns 236
4.1. Population structure 238
4.2. Tagging studies and small-scale movements 240
5. Age and Growth 241
5.1. Estimating age and growth 241
5.2. Length-frequency data 241
5.3. Direct ageing methods 241
5.4. Otolith preparation methods 242
5.5. Validation 242
5.6. Age and growth from otoliths 244
5.7. Growth estimates from tagging 245
5.8. Larval and juvenile growth 247
6. Reproduction 247
6.1. Size at maturity 247
6.2. Fecundity 248
6.3. Timing of spawning 249
6.4. Eggs and larvae 250
7. Trophic ecology 251
Advances in Marine Biology, Volume 58 #2010 Elsevier Ltd.
ISSN 0065-2881, DOI: 10.1016/S0065-2881(10)58004-0 All rights reserved.
* Government of South Georgia and the South Sandwich Islands, Government House, Stanley, Falkland
Islands, FIQQ 1ZZ
{
Fisheries Department, Directorate of Natural Resources, FIPASS, Falkland Islands, FIQQ 1ZZ
{
School of Biological Sciences (Zoology), University of Aberdeen, Tillydrone Avenue, Aberdeen, Scotland,
AB24 2TZ, UK
}
British Antarctic Survey, NERC, High Cross, Madingley Road, Cambridge, CB3 0ET, UK
227
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7.1. Toothfish diet 251
7.2. Feeding rates 258
7.3. Foraging behaviour 258
7.4. Predators of toothfish 258
7.5. Accumulation of mercury in toothfish tissue 261
8. Parasites 262
8.1. Parasite fauna and host specificity 262
8.2. Geographical differences in parasite fauna 266
8.3. Ontogenetic changes in parasite fauna 268
9. Physiology 268
9.1. Buoyancy 269
9.2. Antifreeze glycopeptides 270
9.3. Vision 270
10. Behaviour 271
10.1. Methods of studying behaviour 271
10.2. Baited camera systems 271
10.3. General behaviour patterns 272
10.4. Swimming form and speeds 272
11. Fishery 272
11.1. History of the fishery 272
11.2. Fishing methods and gears 275
11.3. Illegal, unreported and unregulated (IUU) fishing 279
11.4. By-catch issues 280
11.5. Interactions with seabirds 280
11.6. Interactions with marine mammals 283
12. Stock Assessment 285
13. Concluding Remarks 288
Acknowledgements 289
References 289
Abstract
Patagonian toothfish (Dissostichus eleginoides) is a large notothenioid fish that
supports valuable fisheries throughout the Southern Ocean. D. eleginoides are
found on the southern shelves and slopes of South America and around the sub-
Antarctic islands of the Southern Ocean. Patagonian toothfish are a long-lived
species (>50 years), which initially grow rapidly on the shallow shelf areas,
before undertaking an ontogenetic migration into deeper water. Although they
are active predators and scavengers, there is no evidence of large-scale geo-
graphic migrations, and studies using genetics, biochemistry, parasite fauna and
tagging indicate a high degree of isolation between populations in the Indian
Ocean, South Georgia and the Patagonian Shelf. Patagonian toothfish spawn in
deep water (ca. 1000 m) during the austral winter, producing pelagic eggs and
larvae. Larvae switch to a demersal habitat at around 100 mm (1-year-old) and
inhabit relatively shallow water (<300 m) until 6–7 years of age, when they begin
a gradual migration into deeper water. As juvenilesin shallow water, toothfish are
228 Martin A. Collins et al.
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primarily piscivorous, consuming the most abundant suitably sized local prey.
With increasing size and habitat depth, the diet diversifies and includes more
scavenging. Toothfish have weakly mineralised skeletons and a high fat content
in muscle, which helps neutral buoyancy, but limits swimming capacity. Toothfish
generally swim with labriform motion, but are capable of more rapid sub-carangi-
form swimming when startled. Toothfish were first caught as a by-catch (as
juveniles) in shallow trawl fisheries, but following the development of deep
water longlining, fisheries rapidly developed throughout the Southern Ocean.
The initial rapid expansion of the fishery, which led to a peak of over
40,000 tonnes in reported landings in 1995, was accompanied by problems of
bird by-catch and overexploitation as a consequence of illegal, unreported and
unregulated fishing (IUU). These problems have now largely been addressed, but
continued vigilance is required to ensure that the species is sustainably exploited
and the ecosystem effects of the fisheries are minimised.
1. Introduction
Toothfish, named for the sharp teeth on their upper jaw, belong to the
genus Dissostichus in the Family Nototheniidae (Antarctic cods) that are
endemic to the southern hemisphere and dominate Antarctic fish assem-
blages (Gon and Heemstra, 1990; Kock, 1992). There are two species of
toothfish; the Antarctic toothfish (Dissostichus mawsoni), which is found at
high latitudes around Antarctica, and the Patagonian toothfish (D. elegi-
noides;Fig. 4.1), which occurs further north around sub-Antarctic islands
Figure 4.1 Photograph of a Patagonian toothfish (Dissostichus eleginoides) taken with a
baited camera at 1000 m depth on the Patagonian Shelf.
The Patagonian Toothfish: Biology, Ecology and Fishery 229
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such as South Georgia and around the southern tip of South America. There
is, however, some overlap in their distribution in intermediate areas.
Both species grow to large size, reaching lengths in excess of 2.3 m and weights
greater than 200 kg, and are the target of valuable commercial fisheries.
Patagonian toothfish were first described in 1898 (Smitt, 1898), but interest
in the species was limited until toothfish were caught as a by-catch in
trawl fisheries off the South American coasts. The large size of Patagonian
toothfish, coupled with high quality flesh, led to the development, in the mid
1980s, of a valuable longline fishery, targeting large adult Patagonian toothfish
in deep water (>500 m; Agnew, 2004). As with many new fisheries, the fishery
developed ahead of the essential knowledge of the biology and ecology of the
target species that is necessary to facilitate good management practices. Initially,
the longline fishery caused extremely high incidental mortality to seabirds and
while this problem has been largely overcome, there are still concerns about the
sustainability of the various fisheries. In some areas, illegal, unreported or
unregulated (IUU) fishing remains a major problem.
Here, we synthesise existing data on the biology, ecology and fishery for
Patagonian toothfish, highlighting areas where the knowledge is lacking. We
also review the management of stocks of this valuable species in different parts
of its range. We have, where possible, attempted to avoid grey literature.
However there is much valuable information in working group papers from
the Commission for the Conservation of Antarctic Marine Living Resources
(CCAMLR). CCAMLR manges marine living resources south of the
Antarctic Polar Front (APF) and, where necessary, we have cited this work.
2. Taxonomy and Systematics
Order: Perciformes
Sub-order: Notothenioidei
Family: Nototheniidae
Genus: Dissostichus Norman, 1937
Species: Dissostichus eleginoides Smitt, 1898
The Notothenioidei are a suborder of the Perciformes that dominate the
waters of the Southern Ocean. They are an acanthomorph clade of teleost
fish that contain over 120 species (Eastman and Eakin, 2000; Eastman and
McCune, 2000). Within this, the Family Nototheniidae is considered to be
the most speciose and initially included the Eleginopinae, the Notothenii-
nae, the Trematominae and the Pleuragramminae (DeWitt et al., 1990).On
the basis of morphological and molecular data, the genus Eleginops was
removed from the family (Balushkin, 2000; Bargelloni et al., 1998, 2000;
Near and Cheng, 2008; Near et al., 2004; Sanchez et al., 2007). Eleginops
appears as the sister group to all of the nonbovichthid notothenioids, and
230 Martin A. Collins et al.
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this is consistent with the fact that Eleginops is a sub-Antarctic, basal
notothenioid lacking antifreeze proteins. The nototheniids, without Elegi-
nops, are thus divided into three subfamilies based on De Witt et al. (1990)
and Balushkin (2000). These are the Nototheniinae (Notothenia, Parano-
tothenia, Gobionotothen, Lepidonotothen and Patagonotothen), the Trematomi-
nae (Trematomus and Pagothenia) and the Pleuragramminae (De Witt et al.,
1990) or Pleuragrammatinae (Balushkin, 2000)(Dissostichus, Pleuragramma,
Aethotaxis and Gvodarus).
Using molecular data (sequences of MLL, rhodopsin, cytochrome b and
mitochondrial d-loop genes) Sanchez et al. (2007) confirmed Balushkin’s
Pleurammatinae and postulated that neutral buoyancy was gained from
common ancestry as all of the species in this subfamily have this feature.
However they pointed out that the anatomical features of neutral buoyancy
are not the same in Dissostichus, Pleuragramma and Aethotaxis suggesting
parallelisms in neutral buoyancy. Near and Cheng (2008) examined the
phylogenetics of notothenioid fishes using both nuclear and mitochondrial
gene sequences and found the clade containing neutrally buoyant notothe-
nioids present in their mitochondrial dataset but not well resolved in their
nuclear data. They found that, despite common notothenioid clades in both
the nuclear and mitochondrial gene phylogenies, large differences exist in
the phylogenies inferred from each of their two datasets with regard to the
presence of particular clades and the overall phylogenetic resolution. They
concluded that the absence of a monophyletic Nototheniidae and the
neutrally buoyant clade in their nuclear gene tree was a result of a lack of
phylogenetic resolution and not strong support of the paraphyly of these
two groups.
The genus Dissostichus includes two species: the Antarctic toothfish
D. mawsoni and the Patagonian toothfish D. eleginoides.
D. eleginoides was described by Fredrick Adam Smitt in 1898. Smitt
(1898) failed to designate a holotype, but two syntypes were deposited at
the Swedish Museum of Natural History (Naturhistoriska riksmuseet)
(NRM 3235 (1), 3236 (1)). These specimens came from Puerto Torro
(55240S, 068170W) on 11th December 1895 and from Lagotoaia on
10th February 1896.
The etymology of Dissostichus comes from the Greek disso, meaning
double and stichus, meaning row or line referring to its two lateral lines,
whilst eleginoides refers to its morphological affinities to the genus Eleginops.
Subsequently, Gill and Townsend (1901) reported the capture of a fish
of nearly five feet in length from 1900 m by the RV Albatross in 1888 in the
SE Pacific Ocean. Although the specimen was thrown overboard, a photo-
graph was taken of it. The specimen was caught at dredge station 2788, off
the Chonos Archipelago, Southern Chile (45350S, 075550W). The
authors described it from the photograph as Macrias amissus, with the generic
name a reference to its length and bulk, and the specific name reflecting the
The Patagonian Toothfish: Biology, Ecology and Fishery 231
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geographic distance from its relatives as well as the loss of the type. When
DeWitt saw the photograph, he was reminded of the illustrations of D.
eleginoides published by F. A. Smitt in 1888, and after some comparison
of the two, concluded that Macrias amissus was congeneric with Smitt’s
species. De Witt (1962) considered that it should be considered a distinct
species, D. amissus (Gill and Townsend, 1901), differing from D. eleginoides
and D. mawsoni in several ways. De Witt (1962) stated that D. eleginoides
differed from D. amissus in having a longer lower lateral line, a longer head
and snout, a larger eye and longer pectoral fin. Whereas D. mawsoni
(Norman, 1937) differed from D. amissus in having a shorter lower lateral
line, a larger eye, a longer pectoral fin and smaller, more numerous scales.
Using morphometric analyses, Oyarzun and Campos (1987) concluded
that D. amissus is a junior synonym of D. eleginoides by Rule of Priority.
They concluded that the characters used to distinguish between the species
such as eye size, relative head length and the relative lengths of the lateral
lines showed great variability and could not be used to separate the two.
D. eleginoides differs from D. mawsoni by having several elongate scaleless
areas on the dorsal side of its head and by having a longer lower lateral line
(Gon and Heemstra, 1990).
3. Distribution and Life Cycle
3.1. Determining distribution and abundance
A range of methods have been used to sample toothfish and determine
distribution patterns. Initially, toothfish were caught as a by-catch in trawl
fisheries (on the Patagonian shelf and around South Georgia) but, following
the development of the longline fishery in Chile, longlining became the
main fishing method especially in deeper water. Pots have also been trialled
with varying success (Agnew et al., 2001). Baited cameras have been used to
examine distribution and to try to determine density (Collins et al., 1999,
2006; Yau et al., 2002).
Given the broad bathymetric range of toothfish, determination of abun-
dance has proved problematic. Trawl surveys have been undertaken to
depths of around 1000 m (e.g. Coggan et al., 1996), but fishing deeper
requires large amounts of trawl warp, is time consuming and in many areas
the ground is too rough for trawl gear. Baited cameras were initially trialled
on the South Georgia and Falkland Islands slopes (Collins et al., 1999; Yau
et al., 1997, 2002), as a means to estimate abundance. With the baited
camera systems, either the first arrival time of fish at the bait or the total
number attracted from the estimated area of odour plume can be used to
estimate abundance (Priede and Merrett, 1996). However, the initial results
indicated that toothfish may be deterred from attending the bait by the
232 Martin A. Collins et al.
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bright flashes of the camera every 60 s. A follow-up study, which used a
video camera with low-illumination levels, had slightly better results
(Collins et al., 2006), but toothfish attended the bait only briefly, and with
the camera alternating on and off, toothfish may have been missed, so a
reliable estimate of abundance was not possible.
An alternative method to assess adult population size is a mark and
recapture method, using external tags (see Section 4.2). Toothfish are
extremely resilient and post-tagging survivorship is reported as high from
both longlines and short-duration trawls (Agnew et al., 2006a; Williams et al.,
2002). Tuck et al. (2003) used a modified (daily) Peterson mark and recapture
method to assess the population size of toothfish at Macquarie Island. A
length-dependent selectivity model was applied to take account of the move-
ment of tagged fish to deeper water, which was unavailable to the trawl
fishery. Mark and recapture methods have subsequently been used to deter-
mine adult population size in other areas such as South Georgia and the Ross
Sea (Agnew et al., 2006b).
3.2. Geographic distribution
Toothfish have a circum-sub-Antarctic distribution, being found on the
southern Patagonian and Chilean shelves, and around sub-Antarctic islands
(e.g. South Georgia and Shag Rocks, Crozet, Kerguelen, Heard, McDo-
nald, Macquarie and Prince Edward islands), banks (e.g. Banzare Bank) and
seamounts (e.g. Ob and Lena Seamounts) between latitudes 45S and 62S
(Fig. 4.2) in the Southern Ocean (De Witt et al., 1990). The distribution
spans the Antarctic Polar Front (APF) and extends north to 35S on the
Patagonian Shelf in the Atlantic Ocean, to 30S off Chile in the Pacific and
to 40S in the SW Indian Ocean (Abellan, 2005). In the Scotia Sea, the
distribution extends from the Scotia Ridge (west of Shag Rocks) to South
Georgia and the northern South Sandwich Islands, with the most southerly
record in the Scotia Sea being from 61S at King George Island in the
South Orkneys (Arana and Vega, 1999). In the Ross Sea, Patagonian
toothfish are common in the northern areas and have been recorded as far
south as 75300S(Hanchet et al., 2004), with a catch of 14 large individuals
taken on a longline from 1000 m at 71400S(Stevenson et al., 2008), which
was attributed to unusual hydrographic conditions. There remain many
places in the Southern Ocean that have not been sampled, so the known
distribution may be extended.
A single specimen of toothfish was reported from the northern hemi-
sphere (Moller et al., 2003), which was suggested as evidence of long-
distance migration. This record must be considered dubious, as the fish
would have migrated at least 10,000 km, travelling at depths below the
tropical waters.
The Patagonian Toothfish: Biology, Ecology and Fishery 233
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Water temperature may be a key factor in limiting distribution. Unlike
D. mawsoni,D. eleginoides lacks antifreeze and has at least a few glomeruli in
its kidneys (Eastman, 1990), which led to the suggestion that toothfish were
unlikely to occur in water cooler than 2 C(Eastman, 1990). Collins et al.
(2006) photographed Patagonian toothfish at depth in temperatures as low
as 1.4 C, but did not encounter toothfish when the temperature was less
than this.
3.3. Life cycle and bathymetric distribution
Toothfish occupy a broad bathymetric range during their life cycle
(Fig. 4.3). They are known to spawn in deep water during winter ( June–
September) (Agnew et al., 1999; Evseenko et al., 1995; Laptikhovsky et al.,
2006) (see Section 6). Data on the distribution of eggs and larvae are scarce,
but eggs (4.3–4.7 mm) have been found in the upper 500 m over deep
water (Evseenko et al., 1995) and are thought to hatch (at around 15 mm
standard length (SL)) in October–December (Effremenko, 1979; Evseenko
et al., 1995; Kellermann, 1989; North, 2002; North and White, 1982).
Larvae have been caught from around South Georgia (Efremenko, 1984;
Evseenko et al., 1995; North, 2002), Shag Rocks and Burdwood Bank
(North, 2002). The majority of larvae have been reported from an area to
the NW of South Georgia (North, 2002), but this is a heavily sampled
Figure 4.2 Polar projection of the southern hemisphere showing the known distribu-
tion of Patagonian toothfish (Dissostichus eleginoides). Polar Front indicated by the red
dotted line.
234 Martin A. Collins et al.
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location. Of the 43 larvae (18–63 mm SL) reported by North (2002),40
were captured in the upper 250 m, 23 of which were in the upper 3 m at
night.
When the pelagic larvae reach a threshold size, they become bentho-
pelagic and are first caught in research bottom trawls in January at Shag
Rocks at around 150 mm total length (TL) (age 1þ)(Belchier and Collins,
2008), but smaller fish (80–93 mm TL) have been caught on the bottom
near Crozet Islands during February (Duhamel, 1987). The otoliths of
the latter fish had no visible growth increment and were thought to be
7–8 months old. The juvenile phase is typically spent in shallow waters and
the recruitment of these juveniles may be concentrated over a limited spatial
area. For instance, recruitment to the South Georgia population occurs
primarily on the Shag Rocks shelf, to the NW of South Georgia (Collins
et al., 2007). Juveniles typically remain in shallow water for the next 4–5
years. On the Patagonian Shelf, the Isla de los Estados is the main area of
recruitment (Woehler, unpublished), although small numbers of recruits
occur across the southern Patagonian Shelf.
At a size of 500–700 mm TL, the juvenile toothfish disperse and gradually
migrate down the slope, which may be associated with changes in both growth
rate and diet. In general, adult toothfish occupy deep water (>500 m),
although large fish have been caught in shallow water, close inshore, at
South Georgia (Collins et al., 2007). Toothfish thus show the distinct bigger-
deeper trend (Coggan et al., 1996; Collins et al., 2007; Laptikhovsky et al.,
2006; Lord et al.,2006;Fig. 4.3) that is common in many deep-sea scavenging
Juveniles
become
benthopelagic
Adults live in deep water 1000–
2000 m where they feed, moving
only slightly shallower during the
spawning season in July/August to
800–1000 m
Large yolky pelagic
eggs
−3 month till hatch
Larvae remain in upper water layers
500 M
0M
1000 M
Depth m
1500 M
Juveniles migrate into
deeper water as they
grow
Figure 4.3 Schematic illustration of the life cycle of Patagonian toothfish (Dissostichus
eleginoides).
The Patagonian Toothfish: Biology, Ecology and Fishery 235
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fish (Collins et al.,2005) and often associated with a switch from a predatory
role to scavenging (see Section 7,Arkhipkin et al.,2003).
The maximum depth for Patagonian toothfish is around 2500 m, but is
likely to vary geographically, which may be linked to water temperature
(see above). Using baited cameras, Collins et al. (2006) found toothfish as
deep as 1600 m around South Georgia, but no fish were seen in deploy-
ments deeper than 1800 m. Toothfish have been caught down to 2122 m
around the Falkland Islands (Laptikhovsky et al., 2006).
3.4. Recruitment variability
Recruitment of juvenile toothfish, associated with the settlement of pelagic
larvae, shows tremendous inter-annual variability. This is illustrated at
South Georgia, where annual surveys showed a single cohort, first seen in
2003, dominating catches in subsequent years (Fig. 4.4), with little evidence
of further recruitment until 2010 (Collins unpublished). The presence of
dominant cohorts has also been detected in the fishery and through age
determination from otoliths.
Recruitment variability at South Georgia appears to be linked to
environmental variability (Belchier and Collins, 2008). Abundance of
the 1þjuvenile toothfish cohort (13–15 month-old dependent on survey
date) was found to vary inter-annually and to be inversely correlated
with the sea surface temperatures (SST) experienced by adults prior to
spawning. The mean length of 1þtoothfish attained after 13–15 months
was higher in years of high juvenile abundance and was significantly
inversely correlated with SST in the summer prior to adult spawning.
Around the Falkland Islands, peaks in toothfish recruitment have also
been identified, occurring approximately every 4 years (Laptikhovsky
and Brickle, 2005).
4. Population Structure, Movements and
Migration Patterns
Understanding the movements of toothfish at different temporal and
spatial scales is essential to the management of this species. Although the
Patagonian toothfish have a broad circum-Antarctic distribution, the bathy-
metric range of the juveniles and adults means that many island (adult)
populations are potentially isolated from other populations by areas of
deep ocean. Discrimination between different populations/stocks of Pata-
gonian toothfish is an important part of the management process, as it is
important to understand whether individual populations should be managed
in isolation from other stocks. This has stimulated a range of studies that
236 Martin A. Collins et al.
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10
2000
5
0
10
5
0
10
15 1+
2+
3+
4+
5+
6+
5
% Frequency
0
10
15
5
0
10
5
0
10
5
0
10
5
0
10
5
0
10
20
5
0
40 60
Length class (cm)
80 100
2002
2003
2004
2005
2006
2007
2008
2009
Figure 4.4 Length-frequencies of Patagonian toothfish (Dissostichus eleginoides) from
trawl surveys (100–350 m) on the South Georgia and Shag Rocks shelves (modified
from Belchier and Collins, 2008).
The Patagonian Toothfish: Biology, Ecology and Fishery 237
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have investigated the degree of mixing between populations throughout the
Southern Ocean and on the Patagonian Shelf. At a smaller scale, knowledge
of the movements of larvae, juveniles and adults is key to understanding the
life cycle.
Various methods have been undertaken to examine connectivity
between potential populations, including studies on genetics (Appleyard
et al., 2002, 2004; Rogers et al., 2006; Shaw et al., 2004), parasite fauna
(Brickle et al., 2005), biochemical markers in otoliths (Ashford and Jones,
2007; Ashford et al., 2006) and tagging studies (Marlow et al., 2003; Tuck
et al., 2003; Williams et al., 2002), although tagging studies tend to be
informative over shorter temporal and spatial scales.
4.1. Population structure
Genetic studies indicate that a high degree of isolation exists between
Patagonian toothfish populations from different locations, with distinct
populations identified in the southern Indian Ocean (comprising Heard,
Crozet, Kergeluen, Prince Edward and Marion islands), the Atlantic Sector
(South Georgia and the South Sandwich Islands) and the Patagonian Shelf
(Appleyard et al., 2002, 2004; Rogers et al., 2006; Shaw et al., 2004; Smith
and McVeagh, 2000).
Using mitochondrial DNA and micosatellites, initially developed by
Reilly and Ward (1999), Appleyard et al. (2002) found distinct differences
in toothfish populations from Macquarie Island, Heard and McDonald
Islands and South Georgia/Shag Rocks. Greater differentiation of mito-
chondrial DNA was detected and could be explained by either female
philopatry or greater male dispersal. Subsequently, Appleyard et al. (2004)
used the same approach to compare samples from populations at Crozet,
Kerguelen, Prince Edward, Marion and Heard and McDonald islands, and
found no evidence of genetic differentiation between these sites in the
western Indian Ocean.
Genetic studies using mitochondrial DNA sequences (12S rRNA) have
shown a distinct difference between toothfish populations on the Patago-
nian Shelf and those at South Georgia and on the North Scotia Ridge
(Rogers et al., 2006; Shaw et al., 2004). Differences were attributed to the
deep-ocean areas between the sites, which prevent adult migration, and the
APF and sub-Antarctic Front and the associated high-velocity Antarctic
Circumpolar Current, which limits larval dispersal. However, using micro-
satellites, Shaw et al. (2004) found much less distinct population structuring
in the North Scotia Ridge samples and suggested that differences between
mtDNA and nuclear DNA population patterns may reflect either genome
population size effects or (putative) male-biassed dispersal. Rogers et al.
(2006) found that samples from south of the APF (South Georgia,
Bouvet and Ob Seamount) had an identical 12S rRNA haplotype.
238 Martin A. Collins et al.
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However, microsatellite genotype frequencies showed genetic differentia-
tion between South Georgia samples and those obtained from around
Bouvet Island and nearby seamounts. Large geographic distances and
water depths in excess of 3000 m (below the bathymetric range of toothfish)
separate these areas.
The composition of the parasite fauna of toothfish has also been used for
stock discrimination and generally supports the genetic results. Drawing on
previous studies, Brickle (2003) and Brickle et al. (2005) clearly demon-
strated that parasites can be used to separate D. eleginoides populations from
around the Southern Ocean and the Falkland Islands. They showed that
there were significant differences between populations studied, with those
around Heard Island and Macquarie Island showing some similarities. Based
on infra-community structure, they also concluded that a number of indi-
vidual toothfish had, relatively recently, migrated from Heard to Prince
Edward Island.
Oliva et al. (2008) examined the metazoan parasites of D. eleginoides
taken from 629 individuals caught in two localities in southern Chile (Lebu
36S and Quello
´n48
490). They recovered 58,000 parasites from five taxa
and concluded that their data did not support discrete stocks or provide
evidence of any movement between the two localities.
Elemental signatures of otolith margins (Ashford et al., 2005b) and nuclei
(Ashford et al., 2006), determined using an inductively coupled plasma mass
spectrometer (ICP-MS), have also been used to distinguish Patagonian
toothfish from different locations in the Southern Ocean. Otolith margin
signatures of calcium, strontium, magnesium and barium showed differ-
ences between capture areas (Chile, Falklands, South Georgia, Kerguelen
and Macquarie) and between years from the same location (South Georgia).
Otolith nuclei showed clear differences between fish from South Georgia
and the Patagonian Shelf, with a discontinuity at the APF.
Analysis of stable isotopes (dC
13
,dO
18
) in whole otoliths of D. eleginoides
also demonstrated a distinct separation between stocks at South Georgia
and those on the Patagonian Shelf (Ashford and Jones, 2007). Differences
in O
18
were attributed to ambient temperatures of water masses (Antarctic
Intermediate water in the Patagonian shelf region; Circumpolar Deep Water
in South Georgia), whilst differences in C
13
were attributed to dietary
differences.
In summary, the data from a range of sources indicate that separate
toothfish stocks exist in the western Indian Ocean (Prince Edward, Marion,
Crozet, Kerguelen, Heard and McDonald islands), Macquarie Island, the
Atlantic sector (South Georgia and the South Sandwich Islands) and the
Patagonian/Chilean shelf. Fish from Bouvet Island are similar to the South
Georgia population. The relationship between the Ross Sea population and
the Macquarie Island stock is not known.
The Patagonian Toothfish: Biology, Ecology and Fishery 239
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4.2. Tagging studies and small-scale movements
Toothfish have been tagged with traditional T-bar (Agnew et al., 2006b),
dart, passive integrated transponder (PIT), data logging (Williams and
Lamb, 2002) and more recently, pop-up archival tags (Brown et al.,
unpublished). Tagging is an adaptable tool and has been utilised to
examine geographic and bathymetric movements, growth, behaviour
and to estimate population size but all methods can provide data on
movements. Toothfish are relatively robust and, given the lack of a
swim bladder, do not suffer serious decompression injuries when brought
to the surface from depth (Agnew et al., 2006a). Trawl, longline and pot-
caught fish have been successfully tagged and recaptured. Trawl caught
fish are best selected from short-duration trawls, when trauma injuries are
less likely. Longline caught fish can suffer hook damage but survive well,
providing animals in good condition are selected (Agnew et al., 2006a).
Pot-caught animals are generally in good condition, but potting is not
always a commercially viable method of capture. Post-tagging survival is
high and fish have been recaptured after 5 years at liberty (Agnew et al.,
2006b). Tagging is now widely used in assessing population sizes (Hillary
et al., 2006; Tuck et al., 2003), but here, we limit our discussion to data
on movements, with other uses of tagging data discussed elsewhere.
In general, tagging studies indicate that most sub-adult and adult fish
remain within a relatively small area (Marlow et al., 2003; Tuck et al., 2003;
Williams et al., 2002), although small numbers of tagged fish have been
recovered after moving considerable distances. Williams et al.(2002)tagged
5201 (400–1000 mm TL) trawl caught fish on the Heard Island fishing
grounds, recapturing 738. Ninety-nine percent (734) of the fish were recap-
tured within 30 km of their release location after 1–3 years at liberty. However,
three fish were caught on the Crozet Plateau having moved over 1850 km, and
one was recaptured at Kerguelen, 390 km from the tagging location.
Marlow et al. (2003) reported on 37 recaptured fish from the early years
of the South Georgia tagging programme. Of these recaptures, 28 (76%)
were within 25 km of their release location. Two fish had moved 192 and
163 km in an E or SE direction from Shag Rocks towards South Georgia,
consistent with their ontogenetic migration (see above; Collins et al., 2007).
Two other fish caught to the E and NE of South Georgia had moved in
excess of 100 km in a NW direction. By 2005, over 8000 fish had been
tagged in South Georgia, with 304 returns (excluding within year returns)
and had moved an average of 27 km (Agnew et al., 2006b). By 2009 over
25,000 fish had been tagged with over 2000 returns (CCAMLR, 2009).
The population in the north of the South Sandwich Islands may be an
extension of the South Georgia stock. A single fish tagged near the South
Sandwich Islands was recaptured in the South Georgia fishery, approxi-
mately 740 km from the point of release (Roberts and Agnew, 2008).
240 Martin A. Collins et al.
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5. Age and Growth
5.1. Estimating age and growth
Three principal methods have been applied to determining the age and growth
of Patagonian toothfish; direct ageing from otoliths and scales (Horn, 2002;
Hureau and Ozouf-Costaz, 1980), tagging studies (e.g. Marlow et al., 2003;
Williams et al., 2002) and analysis of length-frequency data (e.g. Belchier and
Collins, 2008). Although scales have been used, otolith age readings are the
most widely used method of directly determining age and, when validated,
provide key data for stock assessments. Length-frequency analysis is a less
labour-intensive approach to indicate growth (e.g. Macdonald and Pitcher,
1979), but can be biased by sampling and does not necessarily indicate age.
5.2. Length-frequency data
Whilst growth parameters can be determined from analysis of length-
frequency data (e.g. Collins et al., 2008), in a long-lived species, such as
toothfish, cohorts of adult fish are almost impossible to separate. The length-
frequency data can, however, be informative about growth in the first few
years when cohorts are more easily distinguished. It can also assist with the
interpretation of the first few annuli of otoliths. From trawl surveys at Shag
Rocks and South Georgia, a very strong toothfish cohort was first detected
at modal size 220 mm TL in January 2003 (Fig. 4.4) and was tracked during
surveys in the following years (Belchier and Collins, 2008; Collins et al.,
2007). Given that toothfish spawn in winter and larvae have been caught in
January, it is highly likely that these were 1þfish in 2003 (Belchier and
Collins, 2008). The juvenile toothfish cohort grew by around 100 mm TL
per year and was still present in the sampled population in 2008 (Fig. 4.4).
5.3. Direct ageing methods
The earliest age data were derived from a study undertaken by Zakharov
and Frolkina (1976) on specimens caught at South Georgia, although little
methodological detail was provided. Hureau and Ozouf-Costaz (1980)
subsequently used both otoliths and scales to estimate the age of
D. eleginoides caught at Kerguelen and Crozet islands, whilst Young et al.
(1995) compared the utility of scales and otoliths for age determination of
toothfish caught off southern Chile and found that scales gave significantly
lower age estimates than otoliths in older fish. However, further work by
Cassia (1998) on specimens caught at South Georgia found complete
agreement between ages from scales and otoliths. A detailed comparison
undertaken by Ashford et al. (2001) and lead–radium dating by Andrews
The Patagonian Toothfish: Biology, Ecology and Fishery 241
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et al. (2010) both concluded that the use of scales was likely to lead to an
underestimation of true age in D. eleginoides. Since 2000, all studies on age
and growth of toothfish have relied on age estimates derived from the
analysis of otoliths.
In 2001, a workshop on estimating age in Patagonian toothfish was held
in the Centre for Quantitative Fisheries Ecology with 17 participants from
several countries who were involved in ageing of toothfish. The aims were
to consider toothfish otolith collection and preparation techniques as well as
discuss quality control and validation.
5.4. Otolith preparation methods
Whilst different authors have advocated different methods for otolith
preparation, most involve mounting the otolith in epoxy resin and then
sectioning it transversely through the nucleus. In some cases, the otoliths are
first baked whole for short periods at around 275 C. Sections are then
mounted on slides and examined with reflected light under a binocular
microscope (Ashford et al., 2002; Horn, 2002), although some readers prefer
to use transmitted light (Brown and Belchier, unpublished) (see Fig. 4.5).
Although interpretation of ring patterns in toothfish otoliths can be
problematic (Horn, 2002), they often show clear banding patterns that
reflect the somatic growth of the animal. Wide annuli are deposited during
the first few years of life, a period of fast growth, before slowing at or
following a change in habitat, which is manifested in a transition zone in the
otoliths (Horn, 2002). Horn (2002) reported discrepancies between readers
often caused by interpretation of the location of the first annulus (causing at
least a 1 year error) and the presence of false rings between the first 3–5 years
(leading to larger ageing errors).
5.5. Validation
The use of inaccurate ages has caused serious errors in the management and
understanding of fish populations (Beamish and McFarlane, 1983) and can
be particularly problematic in long-lived fish (Calliet and Andrews, 2008).
Validation of the periodicity of increment formation is therefore essential
before a particular method can be used to provide reliable age estimates of
a species.
Validation that the formation of rings occurs annually in Patagonian
toothfish has been attempted using nuclear bomb radiocarbon tracing
(Kalish and Timmiss, 1998), marginal increment analysis (Horn, 2002),
comparison with length-frequency data and by injecting calcium binding
fluorescent dyes to mark otoliths of fish in tagging programmes
(Krusic-Golub and Williams, 2004, 2005). Kalish and Timmiss (1998) used
‘bomb 14C’ methods on the otolith cores of D. eleginoides, which were
242 Martin A. Collins et al.
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elevated following nuclear testing in the 1960s, to calibrate growth ring counts,
concluding that the counting of annual zones is probably accurate.
Andrews et al.(2010)analysed the Pb/Ra of otoliths from South Georgia,
Heard Island and Kerguelen, providing further confirmation of the
annual deposition of growth increments. Krusic -Golub et al. (2005) used counts
of daily micro-increments in otoliths of fish from Heard Island to validate
the location of the first annulus and found that the average distance
from the primordium to the outer edge of the first translucent zone was
0.630 mm.
Krusic-Golub and Williams (2004, 2005) examined otoliths from 142
strontuim chloride injected and tagged fish (4–18 years old) from the Heard
and McDonald Islands that were recaptured after 350–2571 days at liberty,
to further validate the annual formation of growth rings. In most cases
(88%), the number of rings after the strontium mark corresponded to the,
A
B
1mm
Figure 4.5 Patagonian toothfish (Dissostichus eleginoides) otoliths: (A) photograph of
whole otolith; (B) photomicrograph of a thin transverse section of the dorsal section of
an otolith of fish estimated to be 16 years old. The arrow indicates the position of first
complete annulus and the star indicates the location of the otolith core. Scale
bar ¼1 mm.
The Patagonian Toothfish: Biology, Ecology and Fishery 243
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time at liberty, although this accuracy was reduced (52%) when the reader
was unaware of the time at liberty. Errors were usually of 1 year.
Horn (2002) demonstrated that opaque zones were laid down at the otolith
margins between September and February, with translucent zones laid down
from February to June. All otoliths in June were found to have a translucent
margin, indicating that one translucent zone was laid down annually. How-
ever in this study, there were only three samples from August and none
from July or September, and the samples were aggregated over a number of
years.
Ashford et al. (2002) and Belchier and Collins (2008) used the clear
modal separation of length cohorts of juvenile toothfish caught in trawl
surveys at South Georgia to provide further indirect validation of the otolith
ageing methods. However, Ashford et al. (2002) interpreted the first year
class (200 mm TL) as being 0þfish, but these are almost certainly 1þ.
5.6. Age and growth from otoliths
Otolith-based analyses of the age and growth of toothfish have now been
conducted in all of the major fishery regions since 2000, including the Ross
Sea, South Macquarie Ridge and Southern Campbell Plateau (Horn, 2002),
South Georgia (Ashford et al., 2002; Belchier, 2004) and the Kerguelen
Plateau (Ashford et al., 2005a).
In general, growth is initially fast, with juveniles growing in excess of
120 mm year
1
(Belchier and Collins, 2008), but the growth pattern changes
at ages of 4–8 years, probably associated with a change in habitat and the
ontogenetic down-slope migration. Longevity varies between regions, but
this may be related to sampling bias, as commercial fisheries may not sample
larger, older fish in deep water. Horn (2002) reported that D. eleginoides from
Macquarie Island and the northern Ross Sea reached 54 years of age. Toothfish
are reported to reach 33 years on the Patagonian Shelf (Laptikhovsky et al.,
2006), 36 years around Kerguelen Island (Ashford et al., 2005a) and over 50
years of age at South Georgia (Belchier, 2004).
Growth typically follows the von Bertalanffy pattern, reaching an average
asymptotic size and, in common with many teleost fish, growth rates (and von
Bertalanffy parameters) vary regionally and between sexes (Table 4.1;Fig. 4.6).
Females generally grow quicker and reach larger size than males (Horn,
2002). However, Aguayo (1992) and Young et al. (1992) found no
sexual differences in growth for fish off southern South America, although
females are known to attain a greater size than males in this region (see Moreno,
1998).
Regional differences in growth rate (Table 4.1;Fig. 4.6) may be attrib-
uted to differences in environmental conditions and prey availability
between locations. However, the wide variation in growth parameters
within and between locations suggests that sampling biases and to a lesser
244 Martin A. Collins et al.
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extent variability in otolith annuli interpretation have given rise to some of
the observed differences. Ashford et al. (2005a) noted differences in the age
composition of the catch of toothfish caught by different vessels fishing
within the same region and noted that sampling effects, possibly caused by
differences in fishing gear could generate biases in estimates of age structure.
Unrealistically low estimates of asymptotic length and t
0
(Table 4.1) are
most likely a result of bias from sampling only the fished population for the
derivation of growth curves (Belchier, 2004). Candy et al. (2007) noted that
poor fits of the von Bertalanffy model are in part a result of fishing gear
selectivity, leading to under sampling of both the younger and older parts of
the toothfish population.
5.7. Growth estimates from tagging
With the increase in tagging effort on many toothfish populations, it has been
possible to obtain direct validation of otolith-derived growth models using
mark recapture data. Such an approach has been undertaken for both Heard
and McDonald Islands (HIMI) (Candy et al., 2007) and South Georgia
(Agnew et al., 2006b; Marlow et al., 2003). In both regions, growth in fish
length observed during the time at liberty (i.e. between tagging and recapture)
has been compared with a predicted growth increment based on the otolith-
Table 4.1 Von Bertalanffy growth parameters, derived from otolith increment counts,
for Patagonian toothfish (Dissostichus eleginoides) from different locations and
studies
Regions Sex L
1
Kt
0
Author
Patagonian
Shelf
Female 141.4 0.1500 1.1000 Ashford et al. (2001)
Male 120.7 0.1300 1.5500
South Georgia Female 177.5 0.0820 0.3500 Aguayo (1992)
Male 170.3 0.0860 0.0150
South Georgia Combined 150 0.073 0.792 Belchier (2004)
South Georgia Combined 132 0.08 0.3 CCAMLR 2009
Southern Chile Female 209.7 0.0641 1.1508 Young et al. (1992)
Male 195.6 0.0742 0.7205
Heard Island Female 74.4 0.4800 0.4600 Ashford et al. (2001)
Male 73.9 0.3100 1.7100
Kerguelen Female 103.5 0.1100 4.7000 Ashford et al. (2005a)
Male 95.9 0.1200 4.6000
Macquarie Female 205.3 0.0450 1.5400 Kalish and Timmiss
(1998)Male 138.4 0.0720 1.3700
Macquarie/NZ
EEZ
Female 158.3 0.0850 0.3500 Horn (2002)
Male 134.3 0.1180 0.0800
The Patagonian Toothfish: Biology, Ecology and Fishery 245
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derived growth parameters. At both South Georgia (Agnew et al., 2007)and
HIMI (Candy et al., 2007), there has been generally good agreement between
estimates, but there is some evidence that otolith-derived growth parameters
overestimate toothfish growth when compared to the mark recapture data.
Candy et al. (2007) suggest that this may also be attributed to sampling bias.
However, it is also likely that tagged fish experience some degree of growth
retardation or ‘tag shock’ in which somatic growth is suppressed for an
extended period (as much as a year) post-tagging. Growth retardation from
Age (years)
Females
Females
Males
Males
180
160
140
120
100
80
60
40
20
0
Total length (cm)
0 10 20 30 40 50
Age (years)
180
160
140
120
100
80
60
40
20
0
Total length (cm)
01020304050
Age (years)
180
200
220
160
140
120
100
80
60
40
20
0
Total length (cm)
01020304050
Age (years)
180
200
220
160
140
120
100
80
60
40
20
0
Total length (cm)
01020 30 40 50
180
200
160
140
120
Total length (cm)
100
80
60
40
20
0
010 20 30
A
g
e (
y
ears)
40 50
South Georgia (Ashford et al., 2001)
South Georgia (Aguayo, 1992)
Ross Sea (Horn, 2002)
South Georgia (Belchier and Agnew, 2009)
Macquarie (Kalish and Timimiss, 1998)
South Georgia (Ashford et al., 2001)
South Georgia (Aguayo, 1992)
Ross Sea (Horn, 2002)
South Georgia (Belchier and Agnew, 2009)
Macquarie (Kalish and Timimiss, 1998)
Southern Chile (Young, 1992)
Southern Chile (Aguayo and Cid, 1991)
Central Chile (Rubliar, in preparation)
Falklands (CAF, 1998)
Southern Chile (Young, 1992)
Southern Chile (Aguayo and Cid, 1991)
Central Chile (Rubliar, in preparation)
Falklands (CAF, 1998)
Kerguelen females (Ashford et al., 2005a)
Kerguelen males (Ashford et al., 2005a)
Heard males (Ashford et al., 2005a)
Heard females (Ashford et al., 2005a)
Figure 4.6 Comparison of von Bertalanffy growth curves of Patagonian toothfish
(Dissostichus eleginoides), derived from otolith-based age studies in different geographic
areas. CAF= Central Ageing Facility, Melbourne, Australia.
246 Martin A. Collins et al.
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tagging has been well documented for other fish species (McFarlane and
Beamish, 1990) and it is therefore advisable to exercise caution when estimat-
ing growth from mark-recaptured individuals.
5.8. Larval and juvenile growth
Studies relating to the growth of larval and juvenile toothfish have been
restricted to work on the South Georgia shelf. North (2002) estimated
growth of larval and early juvenile toothfish at 0.8% SL d
1
from pelagic
net samples taken from the north of South Georgia. This growth rate is
around the mid-range of growth rates, of between 0.3% SL d
1
and 2% SL
d
1
estimated for other larval notothenioids at South Georgia during
summer (North, 1998). North (2002) observed annual growth of around
160 mm TL for the first year and noted that this was greater than predicted
from the growth model. However, Belchier and Collins (2008) showed that
there is considerable variability in the mean length attained by juvenile
toothfish in their first year of growth at Shag Rocks. In this study, it was
shown that mean fish length attained after 14 months can vary inter-
annually by greater than 50 mm (TL). It is suggested that growth variability
is related either directly or indirectly to environmental conditions. High
growth rate was associated with strong cohorts, suggesting a positive corre-
lation between juvenile growth and survivorship.
6. Reproduction
Notothenioid reproduction is characterised by protracted gametogen-
sis and low fecundity, with most species not reaching maturity until at least
5 years -old (Kock and Kellermann, 1991). Information on Antarctic and
sub-Antarctic fish suggest that spawning occurs in austral autumn and
winter (Kock and Kellermann, 1991). There is limited information on the
reproductive biology of D. eleginoides in the literature, but some work has
been undertaken around the sub-Antarctic islands, on the Patagonian Shelf
and off the coast of Chile.
6.1. Size at maturity
In Patagonian toothfish, maturity occurs at approximately half of their
maximum length with some variation in 50% maturity values from different
regions and studies (Table 4.2). Everson and Murray (1999) studied the size
at sexual maturity of toothfish caught in the commercial fishery at South
Georgia in 1996 and 1997 and found that there was evidence in 1997 that
25–43% of mature female D. eleginoides did not spawn. They noted that if
The Patagonian Toothfish: Biology, Ecology and Fishery 247
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Lm
50
was calculated without taking this non-spawning into account, it
would lead to an overestimation. Analysis of von Bertalanffy growth curves
indicates that Lm
50
for toothfish is attained between the ages of 6 and 10 for
males, and between 10 and 13 years for females. Skipped or incomplete
spawning has been reported in numerous species of iteroparous fish
(Rideout et al., 2005), with non-spawning occurring due to either retaining
or reabsorbing eggs or the fish remaining in a resting stage. Histological
analysis is needed to determine the nature of this process in toothfish, and it
is likely that in years with higher than average temperatures, a variable
number of toothfish skip spawning which in turn will affect the strength
of recruitment the following year (Brown and Brickle, unpublished data).
This phenomenon has also been suggested by Arana (2009).
6.2. Fecundity
The Patagonian toothfish is the most fecund nototheniid, with absolute
fecundities ranging from 48,900 to 528,900 on the Kerguelen plateau
(Chikov and Mel’nikov, 1990) and between 56,940 and 567,490 in South
Georgia (Nevinsky and Kozlov, 2002). The Chikov and Mel’nikov (1990)
study indicated that there were two size groups in the measured oocytes in
maturing fish caught between March and April. The first mode was between
0.1 and 1.1 mm (protoplasmic oocytes), with the second between 1.4 and
2.9 mm (trophoplasmic), indicating that the maturation of oocytes is
Table 4.2 Length at 50% (Lm
50
) maturity for Patagonian toothfish (Dissostichus
eleginoides) from different locations
Source Area
Lm
50
(mm)
Male Female
CCAMLR (1987) South Georgia 577 1104
Moreno (1998) South Georgia 670 860
Everson and Murray (1999) South Georgia 785 982
Agnew et al. (1999) South Georgia 750 1010
Laptikhovsky and Brickle (2005) Patagonian Shelf 860 900
Prenski and Almeyda (2000) Argentina 763 871
Moreno et al. (1997) Chile 1050 1170
Young et al. (1999) Chile 1287
Oyarzu
´net al. (2003) Chile 780–940 1130–1170
Arana (2009) Chile 810 890
Duhamel (1991) Kerguelen 650 800
Lord et al. (2006) Kerguelen 630 850
248 Martin A. Collins et al.
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discontinuous and synchronous during vitillogenesis, which suggests single
non-intermittent spawning. Larger vitellogenic oocytes were recorded to
increase in volume quickly from a mean diameter of 1.53 mm in March to
1.9 mm in April (Chikov and Mel’nikov, 1990). Of the notothenioids studied
to date, most spawn annually, with the vitellogenic process often taking
2years(Everson, 1977; Kock and Kellermann, 1991; Shandikov and
Faleeva, 1992). Therefore, it is probable that the two stocks of ova which
are seen ripening at different stages in toothfish are for spawning in the current
and following year. Chikov and Mel’nikov (1990) and Nevinsky and Kozlov
(2002) investigated the relationship between fecundity and size (Fig. 4.7).
The former’s estimates are higher than those of the latter authors, which is
probably due to the size range of individuals sampled. Chikov and Mel’nikov
(1990) sampled individuals up to 1300 mm TL, whereas Nevinsky and
Kozlov (2002) sampled toothfish up to 1600 mm TL.
6.3. Timing of spawning
Spawning in Patagonian toothfish generally occurs during the austral winter
(June-September) period (Agnew et al., 1999; Laptikhovsky et al., 2006;
Lord et al., 2006; Arana, 2009). Laptikhovsky et al. (2006) analysed data
collected by observers on longliners operating on the Patagonian Shelf and
reported two spawning peaks for toothfish, a small peak in May and a major
peak in July/August. Females were found to disperse over a greater depth
range than males. They also found that males migrate to the spawning grounds
on Burdwood Bank earlier than females and stay at a depth of 1500–2000 m
until it is time to spawn at approximately 1000 m. Examination of maturity
700,000
600,000
500,000
No of eggs
400,000
300,000
800
200,000
100,000
0
1000 1200 1400
TL (mm)
1600 1800 2000
Chikov and Mel’nikov (1990)
Nevinsky and Kozlov (2002)
Figure 4.7 Relationship between fecundity and size in Patagonian toothfish (Dissos-
tichus eleginoides).
The Patagonian Toothfish: Biology, Ecology and Fishery 249
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data of toothfish caught around South Georgia and Shag Rocks revealed a
large spawning event in late July/August, with a possible smaller spawning
event in April/May, and fish were found to migrate up (females) and down
(males) the slope to meet at the spawning grounds at around 800–1200 m
(Agnew et al., 1999). Lord et al. (2006) showed that toothfish spawning at
Kerguelen occurs between late April/May and mid-July (for females) but
begins later for males (end of May). Off the Chilean coast Arana (2009)
found toothfish with developing gonads in June and July, mature gonads
from July to September, and spent gonads from August to October.
Agnew et al. (1999) reported pre-spawning fish to be distributed all
around the shelf slopes of South Georgia and Shag Rocks whereas both
male and female spent fish were concentrated in the shallower waters to the
northeast of Shag Rocks with very few spent fish being found around South
Georgia. On the Patagonian Shelf, spawning only occurs to the south of the
Falkland Islands. (Laptikhovsky and Brickle, 2005; Laptikhovsky et al.,
2006). In the Pacific, spawning is not found north of 50S and this coupled
with the hypothesised reduced migratory capabilities of toothfish, might
explain the progressive decline in yields north of 47S(Arana, 2009). It is
likely that toothfish north of the Polar Front are at the edge of their range,
thus explaining the southerly location of the spawning grounds in the
Pacific and Atlantic Oceans (Brown and Brickle, unpublished data).
6.4. Eggs and larvae
Once hydrated and spawned, the eggs are 4.4–4.5 mm in diameter with a
rough chorion and large perivitelline space and a homogeneous yolk
(Evseenko et al., 1995).
A number of authors have described various sizes of toothfish from
embryo (Evseenko et al., 1995; Kellermann, 1989), to larvae 11–28 mm
(Ciechomski and Weiss, 1976; Evseenko et al., 1995; Kellermann, 1989)to
larvae/early juveniles 18–63 mm (Effremenko, 1979; North, 2002). Pig-
mentation consists of a band on the posterior post-anal section, single
pigment spots below the pectoral fin, melanophores along the abdominal
region and occipital melanophores on the brain (Kellermann, 1989). Well-
developed canine teeth are present on the lower jaw once larvae reach
20–22 mm SL. The pigmentation remains unchanged during larval devel-
opment, except for the formation of a ventral row of melanophores appear-
ing from the posterior pigment band to the anus (Kellermann, 1989).
Larvae are thought to occur from November onwards and are in the
region of 14 mm at hatching (Kock and Kellermann, 1991). North (2002),
using this size at hatching and early larval growth rates, predicted
that larvae caught around South Georgia hatch between November and
mid December, suggesting a 3.5-month period of embryogenesis.
This is rapid in comparison to other notothenioids; 4–6 months in
250 Martin A. Collins et al.
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Nototheniops nudifrons (Kellermann, 1990) and up to 5 months in Notothenia
corriiceps (Everson, 1977; White et al., 1982).
7. Trophic ecology
7.1. Toothfish diet
Korovina et al. (1991) described the digestive tract of toothfish as consisting of
a large stomach, six to seven pyloric caeca and a digestive tract comprising 87%
of the standard body length. A strongly developed muscular membrane in the
midgut wall (94% of wall thickness) is present, a morphological adaptation
which allows toothfish to consume large quantities of prey.
The diet of adult and juvenile toothfish has been studied using conven-
tional stomach contents analysis on trawl, longline and pot-caught fish
(Table 4.3), and using biomarkers such as stable isotopes and fatty acids
(Stowasser, BAS unpublished). There are clear ontogenetic changes in the
diet of toothfish, associated with the down-slope migration and general switch
to scavenging as size increases. The diet of larval toothfish has not been studied.
The diet of juvenile toothfish (<750 mm TL) has largely been deter-
mined from trawl caught specimens, which are primarily piscivorous,
usually taking the most abundant small fish in their area (Barrera-Oro
et al., 2005; Collins et al., 2007). Zhivov and Krivoruchko (1990) did,
however, find that smaller juveniles (250–400 mm TL) at South Georgia
and Shag Rocks fed mainly on hyperiid amphipods and euphausids.
On the Patagonian Shelf, juveniles take a diverse fish fauna, including
Patagonotothen ramsayi and juveniles of other nototheniid species (Arkhipkin
et al., 2003); however, with increasing size (and depth of occurrence), the
diet changes to include deeper-dwelling and larger species such as hoki
(Macruronus magellanicus) and southern blue whiting (Micromesistius australis).
Garcia de la Rosa et al. (1997) also found the diet of juveniles to be
dominated by fish with cephalopods also taken.
In four summer seasons, Collins et al. (2007) found that the diet of
juveniles at Shag Rocks was dominated by the abundant yellow-finned
notothen (Patagonotothen guntheri), which made up 90% of the diet, whereas
at South Georgia, where P. guntheri is absent, other nototheniids were the
primary prey. In contrast, during March–April 1996, Barrera-Oro et al.
(2005) did not find any Patagonotothen guntheri in the diet, with Lepidono-
tothen squamifrons the most abundant prey species at Shag Rocks; however,
almost 49% of the fish were not identified to species. Some pelagic prey
species have been reported to be taken, including myctophids and Antarctic
krill (Collins et al., 2007; Garcia de la Rosa et al., 1997).
The diet of large, adult toothfish has been studied from both longline
and pot-caught fish. In general, adult toothfish are opportunistic carnivores,
The Patagonian Toothfish: Biology, Ecology and Fishery 251
Author's personal copy
Table 4.3 Diet of Patagonian toothfish (Dissostichus eleginoides)
Location
Depth range
(numbers sampled) Gear and size range Diet summary Main Prey Species Source
South Georgia,
1985–1986
200–400 m (244) Trawl Fish (74 %F); crustaceans
(15 %F); cephalopods
(5 %F)
Unidentified fish
(51 %F); Electrona
carlsbergi (9 %F); crabs
(5 %F); squid (5 %F)
Zhivov and
Krivoruchko
(1990)
400–600 m (217) Trawl Fish (56 %F); crustaceans
(24 %F); cephalopods
(12 %F)
Unidentified fish
(28 %F); E. carlsbergi
(10 %F); lobsters
(24 %F); squid
(10 %F)
Shag Rocks 600–1000 m
(249)
Trawl Fish (77 %F); crustaceans
(14 %F); cephalopods
(7 %F)
Unidentified fish (47 %
F); Patagonotothen
guntheri (10 %F); krill
(4.8 %F)
1000–1400 m
(160)
Trawl Fish (44 %F); crustaceans
(42 %F); cephalopods
(12 %F)
Unidentified fish
(43 %F); crabs (12.5
%F); squid (10 %F)
South Georgia and
Shag Rocks
Trawl; <750 mm TL. Fish (70 %F) Unidentified fish (49 %
F); L. squamifrons,
Champsocephalus
gunnari and
Chaenocephalus
aceratus
Barrera-Oro et al.
(2005)
Shag Rocks, Jan
(2003–2006)
100–400 m (636) Trawl; <750 mm TL Fish (98 %M); crustaceans
(2 % M)
P.guntheri (85 %M);
Gymnoscopelus nicholsi
(4 %M); Euphausia
superba (2 %M)
Collins et al.
(2007)
Author's personal copy
South Georgia, Jan
(2003–2006)
100–400 m (159) Trawl; <750 mm TL Fish (89 %M); crustaceans
(10 %M)
Trematomus hansoni
(23 %M);
Lepidonotothen larseni
(22 %M); C.gunnari
(13 %M); E.superba
(8 %M)
South Georgia and
Shag Rocks,
Dec 87–Jan 88
50–500 m (50) Trawl Fish (96 %F)Muraenolepis sp.
Parachaenichthys
georgianus and
L.larseni
McKenna (1991)
South Georgia and
Shag Rocks,
March–May
2000
200–1650 m
(2268)
Pot; 600–1200 mm
TL
Crustaceans (48 %N); fish
(34 %N); cephalopods
(8 %N)
80% of fish unidentified;
P.guntheri;
myctophids;
Nauticaris sp.;
Paralomis sp.; Thymops
birsteini;E.superba;
Kondakovia longimana;
Pareledone turqueti;
Gonatus antarcticus
Pilling et al.
(2001); Xavier
et al. (2002)
Shag Rocks, May–
August 2000
300–600 m (122) Longline Fish (51 %F); crustacean
(16 %F); cephalopod
(9 %F)
Macrourus sp.,
Muraenolepis spp.,
nototheniids,
channichthyids
Pilling et al.
(2001)
South Georgia and
Shag Rocks,
February 1994
300 m (129) Trawl; 180–900 mm
TL
Fish (86 %F); krill (20 %F)E.superba;
Champsocephalus
gunnari;Gobionotothen
gibberifrons;
Pseudochaenichthys
georgianus;
Nototheniops nudifrons
Garcia de la Rosa
et al. (1997)
(continued)
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Table 4.3 (continued)
Location
Depth range
(numbers sampled) Gear and size range Diet summary Main Prey Species Source
South Georgia and
Shag Rocks,
March–April
1995
1050–1530 m
(226)
Longline Fish (60 %F); squid
(14 %F); crustaceans
(22 %F)
P.guntheri; myctophids;
Antimora rostrata;
Macrourus holotrachys;
Bathydraco sp.,
Chionodraco sp.,
Lycodapus spp.,
Pachycara
brachycephalus,
K.longimana
Macquarie Island,
summer 1995/
96, 1996/97;
1997/98;
500–1290 m
(462)
Trawl; 310–1490 mm
TL
Fish (58 %M); squid (32 %
M); crustaceans (10 %M)
Bathylagus sp. (14 %M);
Gonatus antarcticus
(16 %M); macrourids;
nototheniids and
myctophids
Goldsworthy et al.
(2002)
Argentine Shelf <650 m (135) Shelf. 290–950 mm
TL
Fish (95 %F); cephalopods
(7 %F)
Patagonotothen ramsayi
(26 %F),
Micromesistius australis;
Iluocoetes fimbriatus;
Merluccius hubsi;
Macruronus
magellanicus;Illex
argentinus and Loligo
gahi
Garcia de la Rosa
et al. (1997)
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Falkland Islands,
Apr 1999–Aug
2002
<500 m (135) <400 mm TL Fish (75% F); cephalopods
(21% F)
P. ramsayi (24 %F);
juvenile nototheniids
(20 %F); unidentified
fish (24 %F); Loligo
gahi (24 %F)
Arkhipkin et al.
(2003)
<500 m (366) 400–600 mm TL Fish (73 %F); cephalopods
(22 %F)
P. ramsayi (28 %F);
juvenile nototheniids
(5 %F); unidentified
fish (34 %F); L. gahi
(21 %F)
<500 m (109) >600 mm TL Fish (90% F); cephalopods
(7.3 %F)
M. magellanicus (20.2 %
F); M. australis (18 %
F); unidentified fish
(31 %F); Moroteuthis
ingens (6 %F)
500–1000 m (62) 400–1600 mm TL Fish (72% F); crustaceans
(15 %F); cephalopods
(6 %F)
A. rostrata (29 %F);
unidentified fish
(32 %F); Acanthephyra
pelagica (15 %F);
M. ingens (5 %F)
>1000 m (63) 500–1900 mm TL Fish (61 %F); crustaceans
(43 %F); cephalopods
(5 %F)
A. rostrata (11 %F);
unidentified fish
(37 %F); A. pelagica
(41 %F); M.
holotrachys (6 %F);
unidentified
cephalopods (5 %F)
(continued)
Author's personal copy
Table 4.3 (continued)
Location
Depth range
(numbers sampled) Gear and size range Diet summary Main Prey Species Source
Central and
Southern Chile,
Oct 2001–Oct
2002
>500 m (203) Artisanal fishery;
570–1610 mm TL
Fish (96% IRI) Macrouridae (22%F);
Ophidiidae (16%F);
unidentified fish
(37 %F);
Onychoteuthidae
(5 %F)
Murillo et al.
(2008)
Kerguelen (748) Fish (90 %F)C. gunnari (25 %F) and
L. squamifrons
(12 %F), myctophids
(27 %F)
Duhamel (1981)
Crozet (31) Fish (36 %F); crustaceans
(37 %F); cephalopods
(8 %F)
Nototheniids,
myctophids and
amphipods
Duhamel and
Pletikosic
(1983)
%F= percent frequency of occurrence; %M= percent by mass; %N= percent numbers.
Author's personal copy
feeding on suitably sized locally abundant prey, including a variety of
demersal and pelagic fish, crustaceans and cephalopods. Evidence from
baited cameras (Collins et al., 1999, 2006) and longline captures indicate
the propensity to scavenge food, but the importance of scavenging is not
known and may vary spatially, temporally and ontogenetically.
Studies of adult diet have been undertaken at South Georgia, the Patago-
nian Shelf and around Kerguelen. From a study at South Georgia, Pilling et al.
(2001) showed that the proportion of empty stomachs was generally higher in
longline caught animals than pot-caught animals, which the authors attrib-
uted to an increase in stress-induced regurgitation in line caught fish. How-
ever, there was also a distinct difference in diet between fish caught by the
two methods, with decapod prawns of the genus Nauticaris found in pot-
caught toothfish stomachs. It is possible that the prawns were attracted to the
baited traps and were consumed inside the traps by the toothfish, which
would bias the results of the pot-caught fish. Pilling et al. (2001) also found an
increase in Nauticaris sp. and cephalopods with size (and depth), with a
decrease in the importance of fish. The fish they identified in the diet included
myctophids, nototheniids, Muraenolepis sp., morid cods and grenadiers. The
cephalopod component of the prey from the Pilling et al.(2001) study was
also reported in more detail by Xavier et al. (2002).Garcia de la Rosa et al.
(1997) also examined the diet of adult toothfish at South Georgia and found
fish (mostly unidentified), isopods and the squid Kondakovia longimanna as the
main prey, with lithodid crabs also taken.
Less information is available for toothfish diet in the Indian Ocean
sector, but on the Kerguelen shelf, the diet was also dominated by fish,
with the principal prey being myctophids and the notothenioids Champso-
cephalus gunnari and Lepidonotothen squamifrons (Duhamel, 1981). A relatively
small study at Crozet (74 stomachs) found the main prey (% occurrence) to
be amphipods, with nototheniid and myctophids fish also important
(Duhamel and Pletikosic, 1983).
Many diet studies have focussed on a single season (summer), and diet
may change seasonally, but data on seasonal changes is limited. Arkhipkin
et al. (2003) reported that toothfish (400–600 mm TL) exhibited seasonal
variations in their diet on the Patagonian Shelf. They concluded that
seasonal changes in diet reflected the seasonal variations in prey abundance
on the shelf. Patagonotothen ramsayi was abundant in the diet throughout the
year, whereas Loligo gahi only appeared from February to October during its
offshore seasonal migrations. During November to January, Loligo gahi
migrate inshore to spawn and subsequently disappeared from toothfish
diet. Instead, toothfish consumed southern blue whiting (Micromesistius
australis), which spread out over the shelf after spawning to the south west
of the Falkland Islands.
The Patagonian Toothfish: Biology, Ecology and Fishery 257
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7.2. Feeding rates
Tarverdiyeva (1972) calculated daily rations for D. eleginoides as 5.1% of its
wet body weight per day (at temperatures of 1.2–1.3 C). In studies of diet
of toothfish at South Georgia, Collins et al. (2007) found over 75% of
stomachs examined contained food, with the contents averaging around
2% body weight. Trawls were only undertaken during daylight, but there
was no relationship between fullness and time of day.
7.3. Foraging behaviour
A combination of dietary data, baited cameras and data-logging tags indicate
that toothfish forage in the mesopelagic realm as well as on the seafloor.
Pelagic prey make up a significant part of the diet, and evidence from data-
logging tags shows that toothfish spend some of their time off the seafloor
(Williams and Lamb, 2002), perhaps foraging or utilising currents for
transport. Scavenging is also important, and baited camera work has
shown that large toothfish approach squid or mackerel bait from down
current, presumably using olfaction to detect odour plumes from carcasses
or bait (Collins et al., 1999, 2006). Toothfish appear cautious and circle the
bait before attempting to consume it, but this may be a response to the light,
as footage from baited video cameras shows them repeatedly circling the
illuminated area, before venturing in to grab the bait (Collins et al., 2006).
The bait was attached by wire to a graduated cross and toothfish were seen
pulling the bait off with a jerky motion, before swallowing the squid (bait)
whole. In one case, a toothfish ‘barrel rolled’ through three complete turns
to remove the bait from the cross (Collins et al., 2006).
Live fish kept in captivity have been noted to take pieces of food
(fish muscle) from the bottom of the tank and midwater as it floats down,
and swallow it whole. They initially are seen to ‘smell’ the food. Smaller
fish (<600 mm) were more aggressive during feeding, attempting to
take food from other fish in the tank. On numerous occasions, if two
fish had a hold of a large piece of bait, fish were recorded to ‘barrel roll’
to break the food (Howes, Falkland Fisheries Department personal
communication).
7.4. Predators of toothfish
Data on toothfish predators are rather limited. In shallow water, reported
predators of juveniles include penguins (Brown and Klages, 1987;
Goldsworthy et al.,2001), fur (Green et al., 1989; Reid and Arnould, 1996)
and elephant seals (Green et al., 1989; Reid and Nevitt, 1998; Slip, 1995), but
with increased size and habitat depth, the range of potential predators is likely
to decline (Table 4.4). From extensive studies undertaken at South Georgia,
258 Martin A. Collins et al.
Author's personal copy
Table 4.4 Predators of Patagonian toothfish
Potential predator Maximum depth Comments Sources
Southern elephant seal
Mirounga leonina
Dive to
>2000 m.
Reported to consume toothfish, but importance in
diet not established; potentially a significant
predator
Slip (1995); Reid and Nevitt (1998)
Antarctic fur seal
Arctocephalus gazella
Dive to 300 m Toothfish otoliths occasionally in scats at South
Georgia and Heard Island; unlikely to be a
significant predator
Green et al. (1989), Reid (1995);
Reid and Arnould (1996)
Weddell seal
Leptonychotes weddelli
Dive to 450 m Know to take D. mawsoni in Weddell Sea; small
South Georgia population may take D. eleginoides
Calhaem and Christoffel (1969);
Testa et al. (1985); Plotz (1986);
Lake et al. (2003)
Hooker’s sea-lions
Phocarctos hookeri
Dive to 500 m Toothfish otoliths reported in 42% of scats McMahon et al. (1999)
Sperm whale
Physeter macrocephalus
Dive in excess
of 2000 m
Known to consume toothfish; take toothfish from
longlines; population size at South Georgia is
unknown
Korabelnikov (1959); Clarke
(1980); Abe and Iwami (1989);
Watkins et al. (1993); Ashford
et al. (1996); Purves et al. (2004);
Kock et al. (2006)
Killer whale
Orcinus orca
Dive to 200 m Take toothfish off longlines, but do not dive deep
enough to catch adults
Ashford et al. (1996); Purves et al.
(2004); Kock et al. (2006)
King penguin
Aptenodytes patagonicus
Dive to 300 m Piscivorous, but pelagic feeders generally taking
small fish (myctophids) and squid; no toothfish
reported in diet at South Georgia, but reported in
diet at Crozet (n= 2, 4.3% occurrence)
Kooyman et al. (1992); Cherel et al.
(1996); Olsson and North (1997)
Gentoo penguin
Pygoscelis papua
Dive to 150 m Not known to take toothfish in South Georgia area,
but toothfish recorded in diet at Maquarie Islands
(0.1–1.2% occurrence) and Kerguelen (2.5%
occurrence). Juvenile toothfish noted in diet
around the Falkland Islands
Adams and Klages (1989);
Robinson and Hindell (1996);
Goldsworthy et al. (2001);
Lescroel et al. (2004); Putz et al.
(2001)
(continued)
Author's personal copy
Table 4.4 (continued)
Potential predator Maximum depth Comments Sources
Macaroni penguin
Eudyptes chrysolophus
Dive to 120 m Single incidence of toothfish in diet at Marion
Islands, never recorded at South Georgia
Brown and Klages (1987)
Magellanic penguin
Spheniscus magellanicus
Dive to 150 m Juvenile toothfish noted in diet around the Falkland
Islands
Putz et al. (2001)
Rockhopper penguin
Eudyptes chrysocome
Dive to 150 m Juvenile toothfish noted in diet around the Falkland
Islands
Putz et al. (2001)
Black-browed
albatross
Thalassarche
melanophris
Surface feeders Toothfish in stomachs probably from hooks and/ or
discards from fishing vessels
Cherel et al. (2000, 2002)
Grey-headed albatross
Thalassarche
chrysostoma
Surface feeders Toothfish in stomachs probably from hooks and/ or
discards from fishing vessels
Cherel et al. (2002); Xavier et al.
(2003)
White chinned petrels
Procellaria aequinoctialis
Dive to 10 m Toothfish in stomachs probably from hooks and/ or
discards from fishing vessels
Catard et al. (2000)
Patagonian toothfish
Dissostichus eleginoides
2500 m Some cannibalism likely, with large fish taking
smaller cohorts, but will be limited by the size–
depth distribution pattern
Arkhipkin et al. (2003)
Kingclip
Genypterus blacodes
100–700 m Occasionally predates on small juvenile toothfish on
Falklands Shelf
Nyegaard et al. (2004)
Sleeper sharks
Somniosus sp.
2000 m Toothfish recorded in stomachs, but may be net
feeding and scavenging on discarded heads
Cherel and Duhamel (2004)
Giant Antarctic squid
Mesonychoteuthis
hamiltoni
Unknown Reach large size (>100 kg); incidentally caught on
longline hooks targeting toothfish. Possible
predator, abundance unknown
Collins and Rodhouse (2006);
Collins (unpublished)
Author's personal copy
toothfish are rarely taken by fur seals or penguins and only are occasionally
taken by these species elsewhere (see Table 4.4).
The most important predators of adult toothfish are likely to be large,
deep-diving vertebrates, such as sperm whales and elephant seals, which
have the capacity to dive to the depths which toothfish inhabit. Toothfish
have been recorded in sperm whale stomachs (Abe and Iwami, 1989;
Clarke, 1980; Korabelnikov, 1959) and, although generally considered
squid eaters, they are potentially important toothfish predators. The popu-
lation size of sperm whales in the Southern Ocean is not, however, known,
so the impact is difficult to assess. Elephant seals, particularly males, also have
the ability to dive to the depths that adult toothfish occur and toothfish have
occasionally been identified in their diet (Reid and Nevitt, 1998; Slip et al.,
1994). Sperm and killer whales are both known to take toothfish from
longlines during hauling (Ashford et al., 1996; Kock et al., 2006; Purves
et al., 2004), but adult toothfish habitat is beyond the normal diving
capabilities of killer whales. Antarctic toothfish are known in the diets of
Weddell seals (Ainley and Siniff, 2009), and the distribution of Weddell seals
overlaps with Patagonian toothfish in some places (e.g. South Georgia),
making them a potential predator.
Little is known about the ecology of Mesonychoteuthis hamiltoni, but these
large squid are probably capable of catching and consuming large toothfish,
and are occasionally caught on longline hooks at South Georgia (Collins,
unpublished data).
Albatross and white-chinned petrels are known to take toothfish (Catard
et al., 2000; Cherel et al., 2000, 2002), but these are, almost certainly, fish
that escape from hooks or are discards from fishing vessels. A wandering
albatross has been witnessed swallowing whole a recently tagged 550 mmTL
toothfish (Collins, personal observation).
7.5. Accumulation of mercury in toothfish tissue
As toothfish are large, relatively slow growing predatory or scavenging fish
and occupy a similar top trophic level to large tunas, swordfish and sharks
there has been some concern that their tissues may also accumulate high
levels of mercury (Hg) that could be detrimental to human health when
consumed. A preliminary study of 18 fish by Mendez et al. (2001) showed
that mercury levels ranged between 0.12 and 0.73 mg kg
-1
with some
samples having levels above the EU and Australian limit for mercury in
fish of 0.5mg kg
-1
. A subsequent study on juveniles caught at Macquarie
Island (McArthur et al., 2003) also found mercury levels close to the
recommended maximum and concluded that levels of mercury would
increase as fish grew larger. A recent study by Guynn and Peterson (2008)
demonstrated a clear increase in mercury concentrations in fish muscle with
increasing size but also noted that there were distinct regional differences in
The Patagonian Toothfish: Biology, Ecology and Fishery 261
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overall levels of mercury found in toothfish tissue. Mercury levels found in
fish caught in regions north of the APF (Chilean waters and the Prince
Edward Islands) had far higher levels of mercury than those detected in fish
caught at South Georgia to the south of the APF.
8. Parasites
8.1. Parasite fauna and host specificity
Sixty-two species of parasite have been reported from Patagonian toothfish
from different areas of the host’s distribution (Brickle, 2003; Brickle et al.,
2005, 2006; Gaevskaya et al., 1990; Hamilton, 1995; Oliva et al., 2008;
Parukhin and Lyadov, 1982; Rodriguez and George-Nascimento, 1996)
(Table 4.5;Fig. 4.8). Comparisons of these results have demonstrated major
differences in the parasite fauna of D. eleginoides from different locations
across their range (Brickle, 2003; Brickle et al., 2005; Gaevskaya et al.,
1990).
Thirteen oioxenic species, comprising two microsporideans, four myx-
ozoans, three digeneans, three monogeneans and one acanthocephalan,
have been reported solely from D. eleginoides (Gaevskaya et al., 1990;
Brickle, 2003). However, considering that the knowledge of the ichthyo-
parasite fauna of the sub-Antarctic and Antarctic is poor in comparison to
other regions, it is possible that some of these species may be reported from
other fish species in the future.
Four parasitic species found in D. eleginoides are specific to the Notothe-
niidae and are thus stenoxenic (Brickle, 2003). These include one
nematode, one digenean, one monogenean and one acanthocephalan.
The nematode Hysterothylacium nototheniae was reported from the Ob and
Lena Banks, the acanthocephalan Metacanthocephalus rennicki was only
reported from the Lena Bank and the monogenean Pseudobenedeniella
branchialis occurred in South Georgia.
Forty-three of the parasites reported from D. eleginoides are considered
generalists (eurixenic), which infect fish other than the nototheniids
(Brickle et al., 2005; Gaevskaya et al., 1990; Oliva et al., 2008; Rodriguez
and George-Nascimento, 1996). Six of these species, appear to be specific to
the perciform suborder Notothenioidea. The latter include Dichelyne
(Cucullanellus)fraseri,Lecithophyllum champsocephali,Lepidapedon taeniatum,
Lepidapedon garrardi,Heterosentis heteracanthus and Eubrachiella antarctica.
Clestobothrium crassiceps is considered one of two accidental infections for
D. eleginoides. Specimens were found to infect D. eleginoides from the
Patagonian Shelf (Brickle, 2003) and in a single fish caught at South Georgia
(Gaevskaya et al., 1990). Clestobothrium crassiceps is stenoxenic and usually
found in Merluccius spp. (Esch and Fernandez, 1993), so it is little surprising
262 Martin A. Collins et al.
Author's personal copy
Table 4.5 Geographical distribution of parasites infecting Dissostichus eleginoides from around the Southern Ocean
Type
Geographic range
CPSSGOBLBPEHIMIRS
Microsporidia Microsporidean sp. 1 O ■
Microsporidean sp. 2 O ■
Myxozoa Neoparvicapsula subtile O■
Sphaerospora dissostichi O■
Ceratomyxa dissostichi O■
Alatospora sp. O ■■ ■■ ■ ■
Digenea Brachyphallus crenatus (adult) E ■
Derogenes varicus (adult) E ■■ ■ ■ ■
Digenean sp. 1 (adult) O ■
Elytrophalloides oatesi (adult) E ■■ ■ ■ ■ ■
Glomericirrus macrouri (adult) E ■■■■■
Gonocerca crassa (adult) E ■
Gonocerca phycidis (adult) E ■■ ■ ■ ■ ■ ■ ■
Gonocerca taeniata (adult) E ■
Helicometra antarcicae (Dadult) E ■
Hirundinella ventricosa (larva) Acc ■
Lecithaster australis (adult) E ■
Lecithaster macrocotyle (adult) E ■■
Lecithochirium genypteri (adult) E ■■
Lecithochirium sp. (adult) O ■
Lecithophyllum champsocephali (adult) E ■■■
Lepidapedon garrardi (adult) E ■
Lepidapedon taeniatum (adult) E ■■
(continued)
Author's personal copy
Table 4.5 (continued)
Type
Geographic range
CPSSGOBLBPEHIMIRS
Neolepidapedon magnatestis (adult) S ■■ ■ ■ ■ ■
Neolepidapedon sp. (adult) O
Neolibouria georgiensis (adult) E ■■ ■
Stenakron glacialis (adult) E ■
Monogenea Neopavlovskioides georgianus (adult) O ■■ ■ ■ ■ ■ ■ ■
Neopavlovskioides dissostichi (adult) O ■
Pseudobenedenia dissostichi (adult) O ■■
Pseudobenedeniella branchialis (adult) S ■
Nematoda Anisakis Type 1 (larva) E ■
Anisakis Type 2 (larva) E ■
Anisakis simplex (larva) E ■■ ■ ■
Anisakis spp. (larva) E ■■ ■ ■ ■ ■ ■
Acarophis nototheniae (adult) E ■■ ■■ ■
Capillaria sp. (adult) E ■■ ■ ■
Contracaecum osculatum (larva) E ■
Contracaecum sp. (Nematode, larva) E ■■ ■■■
Dichelyne (Cucullanellus)fraseri (adult) E ■■ ■ ■ ■■ ■
Hysterothylacium sp. (adult/larva) E ■■ ■■■■
Hysterothylacium aduncum (adult/larva) E ■■
Hysterothylacium nototheniae (adult/larva) S ■■■
Pseudoterranova decipiens (adult) E ■■ ■ ■■ ■ ■
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Cestoda Clestobothrium crassiceps (larva) Acc ■■
Grillotia erinaceus (adult) E ■■ ■
Hepatoxylon trichiuri (adult) E ■■ ■ ■ ■
Lacistorhynchus tenuis (larva) E ■
Phyllobothrium sp.(lava) E ■
Pseudophyllidean cercoides (larva) E ■■ ■ ■ ■
Tetraphyllidean cercoides (larva) E ■■ ■ ■ ■ ■ ■
Acanthocephala Aspersentis megarhynchus (adult) E ■■
Corynosoma arctocephali (larva) E ■■■■
Corynosoma bullosum (larva) E ■■ ■ ■ ■ ■
Corynosoma hamanni (larva) E ■■■
Corynosoma pseudohamanni (larva) E ■
Echinorhynchus longiproboscis (adult) E ■
Echinorhynchus petrotschenkoi (adult) E ■■ ■ ■
Heteracanthocephalus dissostichi (adult) O ■■
Heterosentis heteracanthus (adult) E ■
Metacanthocephalus rennicki (adult) S ■
Copepoda Eubrachiella antarctica (adult) E ■■ ■ ■ ■
C = Chile; PS = Patagonian Shelf; SG = South Georgia; OB = Ob Bank; LB = Lena Bank; PE = Prince Edward Islands; HI = Heard Island; MI = Macquarie Island;
RS = Ross Sea. Types of parasite: O = oioxenic (D.eleginoides only); S = stenoxenic (Nototheniidae only); E = eurixenic (wider range); Acc = accidental infection.
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that this parasite was reported from South Georgia (Gaevskaya et al., 1990).
Since merluccids are not reported from south of the APF, the only plausible
explanations are that either a merluccid species strayed from the Patagonian
Shelf or the D. eleginoides in question migrated from the Patagonian Shelf.
The other accidental infection was a single Hirudinella ventricosa, a parasite of
tunas, recovered from a toothfish on the Patagonian Shelf.
8.2. Geographical differences in parasite fauna
Distinct geographic variability has been identified in the parasite fauna of
Patagonian toothfish (Brickle et al., 2005; Gaevskaya et al., 1990; Parukhin
and Lyadov, 1982). Gaevskaya et al. (1990) reviewed work conducted
between 1972 and 1983 from the Patagonian Shelf region, South Georgia,
and the Ob and Lena Banks. Thirty-eight parasite species were found in
these fish, including myxosporideans (1 species), monogenean trematodes
(3), cestodes (5), nematodes (8), acanthocephalans (7), copepods (1) and
digenean trematodes (13).
Gaevskaya et al. (1990) found that the characteristic feature of the
parasite fauna of D. eleginoides was the predominance of helminths, with
92% of them having complex life cycles. They attributed this to the
predatory behaviour of the host and examined the parasite fauna of prey
species in the Patagonian area, to establish the origin of many of the
A
100mm
200mm
100mm
50mm
DEF
BC
Figure 4.8 Parasites of Patagonian toothfish (Dissostichus eleginoides): (A) Echinor-
hynchus longiproboscis vagina and sphincter (Acanthocephala), (B) Corynosoma arctocephali
proboscis (Acanthocephala), (C) Pseudoterranova decipiens (Nematoda), (D) Neopavlovs-
kioidesgeorgianus opisthohaptor (scale ¼40 mm; Monogenea), (E) Pseudobenedenia dissostichi
opisthohaptor (scale ¼300 mm; Monogenea), (F) Grillotia erinaceus.
266 Martin A. Collins et al.
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incidental parasite species found in the host. They suggested that the cestode
Clestobothrium crassiceps infects D. eleginoides through the ingestion of
infected hake (Merluccius spp.), the trematode Gonocerca taeniata through
southern blue whiting (Micromesistius australis australis), the trematodes Lepi-
dapedon taeniata and Glomericirrus macrouri through grenadiers (Macrouridae),
the trematodes Neolebouria georgiensus and Lecithaster australis from fish of the
family Nototheniidae, and acanthocephalans of the genus Corynosoma
through amphipods, isopods and fish of the family Nototheniidae. Many
of these parasites were found sporadically with low intensities.
In the Ob and Lena Banks, Patagonian toothfish appear to obtain the
vast majority of their parasites from their principal prey species, Nototheniops
larsoni (Gaevskaya et al., 1990), notably Hysterothylacium nototheniae,Cucul-
lanellus fraseri and Corynosoma hammani together with other parasites charac-
teristic of nototheniid fish. In the South Georgia area, where the main prey
of toothfish are nototheniid fish, Gaevskaya et al. (1990) identified three
trematodes (Neolebouria georgiensus,Lepidapedon antarcticus,Elytrophalloides
oatesi), two nematodes (Ascarophis nototheniae and Cucullanellus fraseri) and
two acanthocephalans (Echinorhynchus georgianus (¼E. petrotschenkoi) and
Corynosoma bullosum). In general, the parasite fauna of D. eleginoides is
determined to a significant degree by the ichthyoparasite fauna of the area
it inhabits (Gaevskaya et al., 1990) and is richer in the west of its range than
in the east, which indicates that the centre of origin of D. eleginoides was the
Patagonian Shelf (Gaevskaya et al., 1990).
Brickle et al. (2005) reported 32 parasite taxa, including 10 species being
reported from D. eleginoides for the first time, from six locations around the
sub-Antarctic (Shag Rocks, South Georgia, Prince Edward Island, Heard
Island, Macquarie Island and the Ross Sea). Juvenile toothfish from the Shag
Rocks area had a lower species diversity than samples collected from the
other areas, with the exception of the Ross Sea, and Brickle et al. (2005)
suggested that larger fish provide more internal and external space for
infection and can support higher infection rates because they consume
more infected prey.
Brickle et al. (2005) found that some parasite species appeared to be
specific to certain localities. The heaviest infections of larval tetraphyllideans
occurred in immature fish around Shag Rocks, which may be related to
their diet. Microsporidean species and Neolebouria antarctica infected adult
toothfish only at South Georgia. Gaevskaya et al. (1990) also found Neole-
bouria georgiana (¼N. antarctica) around South Georgia and not around the
Ob and Lena Banks. Stenakron sp. and Aspersentis megarhynchus were found
only around Prince Edward Island at relatively high prevalences. Lecitho-
phyllum champsocephali was restricted to Heard, Macquarie and Prince
Edward Islands. Srensen’s similarity index illustrated that the parasite
faunas of D. eleginoides were similar around the sub-Antarctic but showed
The Patagonian Toothfish: Biology, Ecology and Fishery 267
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greater differences with the Ross Sea. The greatest similarities were
between Prince Edward, Heard and Macquarie Island.
8.3. Ontogenetic changes in parasite fauna
Brickle et al. (2005) demonstrated that fish size (but not sex) was a significant
determinant of the parasite fauna of juvenile Patagonian toothfish from Shag
Rocks. There were significant decreases in the abundance and prevalence of
tetraphyllidean (Cestoda) plerocercoides with increasing host length, whilst
the larval acanthocephalan Corynosoma bullosum, the copepod Eubrachiella
antartica, the monogenean Pseudobenedenia dissostichi and the nematode Hys-
terothylacium sp. increased. The reduction in tetraphyllideans was attributed
to the reduction in the eupahasids, intermediate hosts for tetraphyllidean
cestodes, in the toothfish diet. Increases in Corynosoma were likely due to
the presence of intermediate amphipod hosts in the diet, whilst other
increases were associated with increased potential attachment areas.
The nematode Anisakis sp. did not show a significant increase in abundance
with fish length but did show a pattern of increasing prevalence with increasing
fish length. Anisakis spp. use euphausiids as their first intermediate hosts and
squid and fish as second intermediate hosts. Their larvae can be passed onto
other fish and squid without further moults; these squid and fish, therefore, act
as paratenic hosts. Adult Anisakis spp. are parasites of pinnipeds and cetaceans.
D. eleginoides will accumulate increasing numbers of Anisakis spp. by feeding on
infected euphausiids and, later, by feeding on fish. The digenean Gonocerca
physidis and the monogenean Neopavlovskioides georgianus did not show signifi-
cant correlations of abundance with increasing host length. Although Neopav-
lovskioides georgianus showed a pattern of increasing prevalence with length, it is
likely that older/larger toothfish are more suitable hosts for this parasite, and
this is highlighted by the high range of intensities encountered in adult fish
around the sub-Antarctic.
In a detailed study of the parasites of the Falkand Islands’ toothfish
population (11,362 parasites from 27 taxa), Brickle et al. (2006) found
correlations between abundance of certain parasitic taxa and increasing
host length. They also detected differences in the parasite community
with season and depth of capture.
9. Physiology
There is a considerable body of literature on the physiological adapta-
tions that have evolved within the Nototheniidae (see Farrell and
Steffensen, 2005; Kock, 1992 for reviews). The majority of these studies
have focussed on species living at the highest and coldest latitudes where
268 Martin A. Collins et al.
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issues of freezing resistance and cold adaptation are the most acute. Studies
on the physiology of sub-Antarctic and temperate notothens, including
D. eleginoides, are more limited. However, aspects of the physiology of the
congener D. mawsoni have been studied in greater detail allowing inferences
to be made about many, but not all, physiological adaptations to the
environment of D. eleginoides.
9.1. Buoyancy
The majority of notothenioids are benthic and are heavier than sea water,
with all species lacking a swim bladder (Eastman and Devries, 1982).
However, in several species, including those of the genus Dissostichus,a
range of adaptations and mechanisms have evolved to achieve neutral
buoyancy, which conserves muscular energy and enables exploitation of
the pelagic realm (Eastman and Sidell, 2002; Near et al., 2003; Oyarzun
et al., 1988). To compensate for the lack of a swim bladder, Dissostichus spp.,
in common with other members of the clade of neutrally buoyant
notothens, have much diminished mineralisation of the skeleton
(Eastman, 1990). The ash content of the skeleton is only around 6% of
the overall body weight. Cartilage is also substituted for bone in some areas
such as the skull, pectoral girdle and caudal skeleton. Furthermore, the
scales, which also contain heavy bone salts, have an unmineralised portion
at their posterior margin (Eastman, 1990; Oyarzun et al., 1988).
Large lipid deposits, consisting mainly of triglycerols and a small number
of wax esters, also contribute to the buoyancy of D. eleginoides. These lipids
have a specific gravity less than sea water (0.93) and therefore provide
considerable static lift. In a study of specimens caught in the Chilean fishery,
Oyarzun et al. (1988), found that white muscle from the dorsal areas of the
body may contain >25% lipid and may rise considerably (>46%) in regions
close to the centres of mass and buoyancy such as the origin of the pectoral
fin and regions ventral to the pelvic fins. A thick layer of subcutaneous lipid
may account for nearly 5% of the overall body weight but decreases towards
the caudal zone. In Dissostichus species, lipid is stored in typical adipose cells
and is therefore likely to be available for metabolism and hence act as an
energy reserve. The loss of subcutaneous and intra-muscular lipid stores
through metabolism without replacement can lead to an ‘axe handle’
morphology in D. mawsoni with animals having an associated low condition
factor. Emaciation in these fish is most likely caused by the mobilisation of
lipid reserves for migration and reproduction and may lead to fluctuations in
buoyancy throughout the life of the animal (Fenaughty et al., 2008). The
vertebrae of D. eleginoides are also known to contain lipid-filled cavities;
however, it is not thought that the relatively small liver is an organ for
buoyancy. The large pectoral fins of Dissostichus species are also thought to
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provide lift during forward propulsion assisting the ability to maintain
position within the water column.
Near et al. (2003) demonstrated that D. mawsoni experience a distinct
ontogenetic change in buoyancy with juveniles heavier than water (non-
buoyant) and with adults becoming neutrally buoyant at a mean length of
around 810 mm (TL). It is suggested that this could be associated with a
change in habitat use, with juveniles exploiting benthic habitats and adults
foraging within the entire water column over deeper water. Although
directed studies have not been carried out, it is likely that such an onto-
genetic change in buoyancy occurs in D. eleginoides associated with a
marked change in distribution and trophic ecology with size/age
(Belchier and Collins, 2008; Collins et al., 2007). However, in juvenile
D. eleginoides, there is little evidence of benthic feeding, as juveniles are known
to forage above the seabed and feed predominantly on pelagic and semi-pelagic
fish species (Collins et al., 2007). The ontogenetic change in buoyancy may be a
result of a change in prey availability with a need to conserve energy as toothfish
move to greater depths where prey are more scarce.
9.2. Antifreeze glycopeptides
The evolutionary development of antifreeze compounds has been essential
for fish survival in many of the colder, higher latitude habitats of the
Southern Ocean and has enabled the radiation of many notothenioids into
these environments. A major physiological-biochemical adaptation has
been the ability to synthesise macromolecular antifreeze substances for
circulation in the body fluids. These antifreezes prevent notothenioids
freezing when they come into direct contact with ice. However,
D. eleginoides, which generally live in water temperatures of 2–11 C, lack
antifreeze within their body fluids. The congener D. mawsoni possesses eight
antifreeze glycopeptides (AFGPs), which are synthesised in the liver.
Ghigliotti et al. (2007) noted that whilst D. mawsoni has high levels
of circulatory AFGPs and an associated high level of AFGP genes,
D. eleginoides has barely detectable AFGP sequences in its DNA.
The authors suggest that despite their close phylogenetic kinship, the
evolution of these species in disparate thermal regimes means that they
show some distinct genetic and biological characteristics.
9.3. Vision
Whilst there have been no studies to date on the optical physiology of
D. eleginoides, an extensive comparative study of the ocular morphology of
Antarctic notothenioids included a detailed examination of the morphology
of the eye of D. mawsoni (Eastman, 1988). As the two congeners show much
similarity in behaviour, morphology and ecology, it is likely that the
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adaptations to eye morphology observed in D. mawsoni are also present in
D. eleginoides. In a study of the gross and microscopical anatomy of 18
species found in the sea ice zone in McMurdo Sound, Antarctica,
D. mawsoni was shown to possess by far the lowest number of cones and
the highest ratio of rods/cones in the retina of all species examined. The
rod-dominated retina of Dissostichus is especially sensitive and well suited to
respond to dim light levels at depth. The huge reduction in the number of
cones is typical of deep-water species and serves to increase the sensitivity of
the retina whilst reducing the visual acuity. It is not certain whether juvenile
Dissostichus have the same eye morphology as adults or whether there is a
change in eye development during the ontogenetic movement into deeper
water. It is clear that adult toothfish can migrate vertically throughout the
water column and have often been caught in relatively shallow depths
(<40 m) close to the shore. Collins et al. (1999, 2006) noted the sensitivity
of toothfish to flashes and lights associated with underwater photography,
including the ability to rapidly change colour, which clearly indicates a
highly developed visual system.
10. Behaviour
10.1. Methods of studying behaviour
Data on Patagonian toothfish behaviour come from three main sources,
observations of captive animals, baited camera systems (conventional 35 mm
and video) and from data-logging tags (Williams and Lamb, 2002) that have
been attached to toothfish.
10.2. Baited camera systems
Adult toothfish are readily attracted to bait, which makes them susceptible to
baited longlines, but also enables them to be studied using baited cameras.
Baited cameras have been used to investigate the abundance and behaviour of
toothfish on the Patagonian Shelf (Collins et al., 1999) and on the shelf around
South Georgia and Shag Rocks (Collins et al., 2006; Yau et al., 2002). The
baited camera work was undertaken using autonomous lander systems (Priede
and Bagley, 2000) that were dropped to the seafloor, ballasted with scrap
metal and remained on the seafloor for periods of a few hours to weeks. Initial
work on toothfish utilised a high-resolution 35 mm camera with powerful
flash lights (200 J), but the data suggested that the lights discourage the
toothfish from attending the bait, and the number of encounters was small
(Collins et al., 1999; Yau et al., 2002). Later work utilised a low-light video
camera and many more toothfish encounters were recorded (Collins et al.,
2006; Yau et al., 2002).
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10.3. General behaviour patterns
Toothfish appeared to be solitary and generally avoided one another. Any
accidental contact between conspecifics resulted in sudden departure in differ-
ent directions; similarly, unintended contact with the stone crabs (Lithodidae)
also led to the rapid departure of the toothfish. Unlike other deep-water
scavengers, toothfish did not accumulate at the bait, instead fish took a piece
of bait and rapidly departed. No attempts were made to approach the bait when
large numbers of stone crabs were clustered around it (Collins et al., 1999, 2006).
10.4. Swimming form and speeds
Observations from baited video cameras (Collins et al., 2006) and captive
animals (Brown, unpublished) show that labriform swimming (sculling with
the large pectoral fins) is the principal means of locomotion in Patagonian
toothfish. This gentle sculling with the pectoral fins produces relatively slow
cruising speeds with a mean of 0.17 m s
1
or approximately 0.22 BL s
1
(Collins et al., 2006; Yau et al., 2002). The pectoral fins are also used in a
gliding motion, particularly when toothfish swim close to the seafloor. Sub-
carangiform swimming (using the caudal trunk and fin) was also observed
typically during turning or rapid acceleration. The maximum swimming
speed recorded was 2.23 m s
1
for an individual of 0.72 cm TL (3.1 BL s
1
)
when the fish was in ‘panic flight’ (Yau et al., 2002).
Using tagging data, Agnew et al. (2006a) reported an average distance
moved by toothfish around South Georgia, at 10 km year
1
indicating little
large-scale movements. D. mawsoni and D. eleginoides are comprised of a large
percent of white muscle (51% of the body weight in D. mawsoni (Eastman
and Devries, 1981)), resulting in most of their movement being dominated
by small periods of rapid movements, and their reduced amount of red
muscle, for slow sustained swimming, explains their strong site fidelity.
From archival data storage tags deployed on toothfish around Heard
Island (Williams and Lamb, 2002), toothfish of 710–820 mm TL were
recorded making daily movements both upwards and downwards, of
between 20 and 130 m (mainly <60 m). They concluded that this behaviour
was in response to several factors, including environmental parameters (day
and lunar phase), behaviour of prey species and bottom topography.
11. Fishery
11.1. History of the fishery
Patagonian toothfish were first investigated as a fisheries resource in Chile in the
1950s (Guerrero and Arana, 2009; Moreno, 1991), with exploratory trawling
limited to shallow depths. Toothfish were subsequently caught as a by-catch in
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trawl fisheries around Kerguelen Island, on the Patagonian Shelf and around
South Georgia in the early 1980s. Development of longline gear capable of
operating in deep water, targeting the large adult fish, led to the targeted fishery
in Chilean waters, which began in the mid-1980s and quickly spread to other
areas such as the Patagonian Shelf, South Georgia and Kerguelen. The high
price commanded by toothfish (currently US$15 per kg) led to a rapid expan-
sion in the catches, with new fishing grounds identified and targeted. The FAO
reported that landings increased from less than 5000 tonnes in 1983 to
40,000 tonnes in 1992 (Fig. 4.9), although these figures include only the legal
catches within the CCAMLR area and national territorial waters.
At South Georgia (UK Overseas Territory), the longline fishery began with
Soviet Union vessels in late 1988, which were later joined by Chilean,
Bulgarian and Ukrainian vessels. In 1993/1994, CCAMLR designated the
South Georgia region as a special area for protection and scientific study and
undertook a depletion experiment to determine stock size. The depletion
experiment was not successful (Parkes et al., 1996), but the presence of
observers on board demonstrated the severity of the seabird by-catch problem
and led to the fishery being limited to the winter months from 1998 (Agnew,
2004). Since 1999, the season has been restricted to the period from May 1st
until August 31st, with opportunities for a season extension of 2 weeks into
September and at the end of April for vessels that were fully compliant with
management measures the previous year (CCAMLR, 2009). In recent years,
the total allowable catch (TAC) in the South Georgia fishery has been around
1980 1985 1990
Year
1995 2000 20051975
50,000 FAO annual landings
40,000
30,000
Tonnes
20,000
10,000
0
South Georgia
SE Atlantic
SW Atlantic
Indian Ocean
Pacific, Antarctic
SE Pacific
SW Pacific
Figure 4.9 Annual landings of Patagonian toothfish (Dissostichus eleginoides)from
different regions. Data based on FAO figures. Note that this only includes reported
landings.
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3000 tonnes. A small fishery also operates around the northern area of the
South Sandwich Islands (Roberts and Agnew, 2008), with the TAC currently
41 tonnes (CCAMLR, 2009).
In the southern Indian Ocean, a targeted trawl fishery began on the
western Kerguelen shelf (French exclusive economic zone (EEZ)) in 1984/
1985, when former USSR trawlers found and began to exploit large con-
centrations of toothfish (Lord et al., 2006). Longlining started in the Ker-
guelen fishery in 1991, and since 2001/2002, the fishery has been
exclusively longliners (Lord et al., 2006). The Kerguelen fishery operates
year round, although catch rates are lower in winter, and since 1994, the
legal catches have been around 5000 tonnes per year. The Heard and
McDonald Islands (HIMI) shelf (Australian EEZ) is contiguous with the
Kerguelen shelf and is probably the same population of toothfish. Apart
from some Polish research fishing in the 1970s, there was little known
exploitation on the HIMI shelf (Williams and de la Mare, 1995) until
trawl fisheries developed for toothfish and icefish in 1996. The fishery was
opened up to longlining in 2002/2003 and is currently exploited by both
trawlers and longliners, with a catch limit of around 2500 tonnes.
At Crozet Island (French EEZ), 900 miles west of the Kerguelen
Plateau, the longline fishery began in 1996/1997, with reported catches of
up to 1200 tonnes, but the fishery suffered from considerable illegal fishing
activity from 1995 to 2002. Current legitimate catches are less than
1000 tonnes per year.
The Prince Edward Islands (South African EEZ) fishery, which spans the
edge of the CCAMLR zone, began in 1996/1997 as a seasonal fishery (May
1st–August 31st), but the fishery suffered from high levels of illegal catches,
with an estimated 21,000 tonnes illegally taken in 1997 (Brandao et al., 2002).
In an attempt to counter the illegal fishing, the fishery was opened year round
in 1998, in the hope that the presence of legal operators would deter the
illegal vessels (Brandao et al., 2002), but catch rates and legal catches declined
sharply. The TAC in 2002/2003 was set at 400 tonnes and recent estimates of
IUU are zero, with legal catches of around 200 tonnes per year.
Elsewhere in CCAMLR waters, toothfish fishing has occurred on
isolated banks and seamounts, such as Banzarre Bank and the Ob and
Lena Seamounts. The fisheries in these areas were rapidly overexploited
and stocks remain depleted (McKinlay et al., 2008).
The Macquarie Island (Australian EEZ) fishery began in late 1994 in the
Aurora Trough and spread to the Macquarie Ridge 2 years later when
toothfish aggregations were detected. Initially, catches were over
1000 tonnes per year, but the fishery was closed (except for research fishing)
from 1999 to 2003, when it resumed with a reduced TAC (Phillips et al.,
2009). Although trawling has been the main method of fishing since 1994, a
3-year longline trial began in August 2007, primarily on the Macquarie
Ridge north and south of the island. Current quotas are around 300 tonnes
274 Martin A. Collins et al.
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from the Aurora Ridge, with 100 tonnes from Macquarie Ridge (Phillips
et al., 2009).
Toothfish were initially taken as by-catch in trawl fisheries on the
Patagonian Shelf, with longline fisheries subsequently established in Argen-
tine and Falkland Island waters. The Argentinian fishery started in the 1990s
with the highest catches in 1995 (18,225 tonnes); however, catches have
declined since then (Wohler, unpublished data). Based on advice from the
National Institute of Fishing Research and Development (INIDEP), new
management practices have been enforced by the Fishing Authority since
2000. These include catch documentation scheme (CDS), larger hook sizes,
minimum fish size, minimum fishing depths and establishment of a pro-
tected juvenile area.
The Falklands longline fishery began in 1992 as an experimental fishery
and became an established fishery in 1994 (Laptikhovsky and Brickle, 2005).
Catches peaked in the first year of the directed fishery (2733 tonnes in 1994)
and subsequently stabilised to a level of 1200–1800 tonnes (currently,
1200 tonnes).
The Chilean fishery is divided into two zones. The north zone, between
Chile’s northern limit (18210S) and 47S, is reserved exclusively for
artisanal fishing, whereas in the south zone (47Sto57
S), the resource is
exploited through industrial fishing activities (Guerrero and Arana, 2009).
The only gear permitted is the demersal longline, although pots have been
trialled (Guerrero and Arana, 2009). The Chilean fishery has also been
instrumental in developing new gears, such as the trotline and cachalotera
system (Moreno et al., 2006, 2008, see below).
Areas in the high seas (outside of national jurisdiction) have also been
exploited, notably the Scotia Ridge between Shag Rocks and the Falklands.
In these areas, catches have not been limited and stocks quickly depleted.
11.2. Fishing methods and gears
The principal method of catching adult toothfish is demersal longlining
(see Figs. 4.10 and 4.11), in which a longline of baited hooks are deployed
close to the seafloor at depths up to 2000 m. Surface buoys indicate the
presence of lines, and vessels typically recover lines after a ‘soak-time’ of
24–48 h. Bait is usually squid or sardine. Longline vessels are generally small
vessels (30–80 m; Fig. 4.10). There are three principal types of longlining:
the Spanish (double-line) system, autoline and more recently, the trotline
system (Fig. 4.11), which often includes cetacean exclusion nets (umbrellas
or cachaloteras). In all cases, lines are deployed from the stern of the vessel
and recovered via a hauling hatch on the starboard side.
The Spanish or double-line system (Fig. 4.11A) uses a strong main- or
mother-line attached at each end to an anchor and buoy line. The fishing
line is attached to the main line by a series of connecting ropes. The hooks
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are attached to the fishing line with monofilament snoods, with each section
of the fishing line comprising around 25 hooks, with around 7000 hooks per
line and with vessels deploying 2–3 lines per day. Weights (6–10 kg) are
attached between each section of hooks to sink the line and keep it on the
seafloor. The hooks are baited by hand, which is relatively labour intensive.
A
B
C
D
Figure 4.10 The fishery for Patagonian toothfish (Dissostichus eleginoides): (A) photo-
graph of an autoliner; (B) aerial photograph of a Spanish double-line longliner, note the
hauling area on the starboard side; (C) toothfish being gaffed; (D) circle-type (left) and
J-type hooks used in the South Georgia fishery.
276 Martin A. Collins et al.
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The autoline system (Fig. 4.11B) has a single weighted line (polypropyl-
ene line with integrated weight, around 50 gm
1
), from which hooks are
attached via swivels and multifilament snoods. The line is divided into
magazines, each consisting of 1000–1500 hooks, and although the length
of lines and hence the number of hooks varies, typically an autoliner will be
able to deploy 30,000 baited hooks per day. Hooks on auto-lines are
automatically baited.
Trotlines (Fig. 4.11C) were initially developed in the Chilean artisanal
fishery (Moreno et al., 2008) and are a modification of the Spanish system, in
which the hook line is replaced by a series of vertical branch lines, placed at
40 m intervals. Each of the vertical branch lines supports clumps of 8–20
short hook lines and, at its extremity, a bag of weights. In the Falklands,
there is one clump of 8 hooks per branch line with a single 6 kg weight at
the bottom (Brown et al., 2010). The clumping of the hooks near the
weights allows the baited hooks to sink rapidly to avoid seabirds, but the
method also allows for the use of net sleeves, umbrellas or cachaloteras to
reduce depredation by whales (see below). Each branch line can have a
buoyant net or sleeve attached that is able slide up and down the line.
A
Main line
Main line
Weights
Weights
B
C
Integrated weight line
Figure 4.11 Illustration of the three methods of longlining: (A) Spanish double-line
system, (B) autoline system and (C) trotline with net sleeves.
The Patagonian Toothfish: Biology, Ecology and Fishery 277
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During the set, this sleeve remains at the upper end of the branch line, but
when the thick main line is hauled, the movement of the vertical branch
line through the water causes the sleeve to slide down the line covering the
hooks and any captured fish.
Pots were initially trialled as a method of reducing seabird mortality (see
below) and also to stop depredation by sperm and killer whales. The traps
(Fig. 4.12) used are typically a truncated conical shape, with a circular base of
around 1.5 m, an upper part of 0.9 m diameter and 0.9 m high and made of
steel and mesh panels (120 mm for the body and 38 mm for the mouth). Pot
fishing is used in the fishery on the Patagonian Shelf and southern Chile, but
has not proved successful at South Georgia, where catch rates were substan-
tially lower than longlines (Agnew et al., 2001; Guerrero and Arana, 2009).
There has been considerable regional variability in the success of differ-
ent fishing methods, which is probably a consequence of bottom topogra-
phy, current speeds and, possibly, toothfish behaviour. The autoline system
has not been successful in the Falklands, but works well in other areas such
as South Georgia and Heard Island. With the trotline system, catches
(g/hook) are usually less at high toothfish density, probably because it is
rare for each clump of hooks (8–20) to catch more than two fish. In the
Falklands the catch per unit effort (CPUE) has been reported to be up to ten
times higher with umbrella lines than Spanish longlines (in the same area);
however, this is not a linear relationship, with Spanish lines performing
better in areas of high local abundance of toothfish (Brown et al., 2010).
The Falklands fishery initially used the Spanish system, but has recently
switched to using trotlines with cachaloteras.
Figure 4.12 A typical pot used to catch toothfish in the Falkland Islands Patagonian
toothfish (Dissostichus eleginoides) fishery.
278 Martin A. Collins et al.
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Gill nets have also been used to catch toothfish, but are banned through-
out CCAMLR waters, as they have the potential to ‘ghost fish’ if the gear is
not recovered. Gill nets are, however, used by illegal, unreported and
unregulated (IUU) vessels (see below) that fish in the Southern Ocean.
Bottom trawling is used to target toothfish on the shelf-slope at Heard
Island. However, bottom-trawling is less discriminate than longlining, with
a greater by-catch and is also likely to cause considerably more damage to
seafloor habitats.
Different types and sizes of hooks have been used to catch toothfish. The
commonest types are the ‘circle’ and ‘j’ hooks (Fig. 4.11D). The type and
size of hook can influence the size and quantity of both target and non-
target species. Bait is usually sardine and/or squid. Sardine, being an oily
fish, produce good odour; however, as they have softer flesh than squid, the
sardine generally do not last as long on the hooks, as they are consumed by
amphipods. A combination of the two types of bait is considered to produce
the best catch rates by many fishermen.
11.3. Illegal, unreported and unregulated (IUU) fishing
IUU fishing has been a major problem in toothfish fisheries throughout the
southern hemisphere (Baird, 2006; Lack, 2008; Lack and Sant, 2001). The
high value of the catch and difficulties of enforcing regulations in such a
large and inhospitable ocean led to the development of significant illegal
fishing in the early 1990s. This undoubtedly had a detrimental effect on the
toothfish stocks and, since IUU vessels are unlikely to follow mitigation
measures, on by-catch of seabirds (as described later) and non-target species.
In CCAMLR waters, IUU fishing started in 1992 around South Georgia
(Agnew and Kirkwood, 2005). Following a series of arrests by U.K. autho-
rities in that area, IUU operations moved to the Indian Ocean sector in
1996 and 1997 after the identification of large areas there where toothfish
could potentially be caught. Since then, most activity has been concentrated
on fishing grounds around Prince Edward and Marion Islands (South
Africa), Crozet and Kerguelen Islands (France), Heard Island (Australia)
and on oceanic banks in high seas areas such as the Banzare Bank.
CCAMLR and its member states have introduced a number of measures
designed to reduce the level of IUU. These include the CDS (Agnew,
2000), satellite-derived tamperproof vessel monitoring systems (VMS) and
rigorous patrolling, with high-profile arrests and prosecutions. Vessels fish-
ing in CCAMLR waters must also carry an international observer and
provide regular catch reports. The CDS, which was adopted in 2000,
applies to both species of Dissostichus and is designed to demonstrate if
toothfish were caught in compliance with conservation measures by track-
ing landings and trade. If a consignment of toothfish does not have the
necessary documentation, it is assumed to be IUU. Under the VMS, every
The Patagonian Toothfish: Biology, Ecology and Fishery 279
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vessel licensed by CCAMLR members to fish in the Convention Area is
required to have a VMS, monitored by the flag State and forwarded to the
CCAMLR Secretariat. This information can then be used to corroborate
toothfish landings in the CDS. Some CCAMLR member states have taken
additional steps in the fisheries that they manage in their territory. For
instance, in the South Georgia fishery, which has been certified as sustain-
ably managed by the Marine Stewardship Council, all toothfish products are
weighed and verified at the end of the season. This ensures that licensed
vessels do not exceed their allocated quota.
CCAMLR estimate the amount of toothfish taken by IUU vessels and
include this data in stock assessments (CCAMLR, 2009), but Lack (2008)
analysed trade data and suggested that CCAMLR may underestimate IUU
catches by up to 50%. In 2002, a proposal to list toothfish on Appendix II of
the Convention on International Trade in Endangered Species (CITES)
was subsequently withdrawn, recognising that the CCAMLR CDS already
monitors trade in toothfish.
Not all Patagonian toothfish fisheries are in the CCAMLR area (e.g. Chile,
Argentina, Falklands, Crozet, Macquarie Island), and in these areas, domestic
legislation and enforcement are relied upon to address IUU fishing.
11.4. By-catch issues
Although more selective than trawling, longlining still generates a by-catch.
The principal by-catch species are grenadier (Macrouridae), morid cods
such as Antimora rostrata (Moridae) and skates (Rajidae). By-catch levels vary
between regions and depths, and also between fishing methods and with
hook type and size and bait. At South Georgia, the by-catch of grenadiers is
considerably greater with the autoline system than the Spanish double-line
system. Species that possess a swim bladder (e.g. macrouids, morids) suffer
severe decompression trauma when brought to the surface and will not
survive if returned. Survival of species that lack a swim bladder can be high
and in CCAMLR fisheries vessels are required to release (some with tags) all
skate that are in good condition when caught. Longlines also capture and
damage benthic invertebrates and the need to protect Vulnerable Marine
Ecosystems (VMEs), such as those associated with cold-water corals, is a
high priority within CCAMLR and other fisheries (Martin-Smith, 2009;
Sharp et al., 2009).
11.5. Interactions with seabirds
Interactions with seabirds are a problem with many longline fisheries
(Brothers, 1991). Scavenging seabirds, including many albatross and petrel
species, are attracted to baited hooks when they are deployed and, when
they dive for the bait, they become hooked, sink with the lines and drown.
280 Martin A. Collins et al.
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This has been a major problem within the majority of Patagonian toothfish
fisheries in the Southern Ocean (Ashford et al., 1994, 1995; Delord et al.,
2005, 2010; Moreno et al., 1996; Nel et al., 2002; Reid et al., 2004;
Williams and Capdeville, 1996), many of which operate in important
foraging areas for threatened albatross and petrel species (Fig. 4.13). In the
late 1980s, large numbers of seabirds were killed, but not quantified.
5000
1000
500
0
1000
1000
Numbers
500
500
0
0
10
5
0
15,000
10,000
5000
0
6000
South Georgia
Prince Edward Islands
Crozet
Heard Island
Kerguelen Island
2352
No data
1998
19431224417
235 314
131 93
No data
000
0000
2
2000 2002 2004 2006
Year
2008
Figure 4.13 Numbers of seabirds reported killed in fisheries for Patagonian toothfish
(Dissostichus eleginoides) at Kerguelen, Heard and Macdonald, Crozet, Prince Edward
Island and South Georgia.
The Patagonian Toothfish: Biology, Ecology and Fishery 281
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In 1992, CCAMLR responded to the seabird mortality issue and
adopted a suite of mitigation measures, including the use of streamer lines,
night setting and controls on offal discharge. The ad hoc working group on
incidental mortality associated with longline fishing (IMALF) was then
established in 1993 to monitor the problem and develop further mitigation.
The CCAMLR Scientific Observer Scheme, which was also adopted in
1992, ensured 100% observer coverage on toothfish vessels, to monitor
mitigation and by-catch. Additional mitigation measures included line-
weighting schemes (Agnew et al., 2000; Robertson et al., 2000, 2007;
Wienecke and Robertson, 2004) to ensure that hooks sink rapidly, the
use of streamer or Tori lines during shooting (Fig. 4.14A) and the ‘Brickle
Curtain’ (seven weighted vertically hung lines which form a curtain;
Fig. 4.14B) to keep birds from the hauling area.
A
B
Figure 4.14 Seabird mitigation methods in action on a longliner; (A) streamer or Tori
lines; (B) Brickle curtain around hauling area.
282 Martin A. Collins et al.
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Further restrictions were introduced on fisheries under CCAMLR
management, including the closure of the South Georgia fishery during
the summer months, when species such as white-chinned petrel are partic-
ularly susceptible to capture. The mitigation measures implemented by
CCAMLR had the desired effect, with the bird by-catch now close to
zero (Fig. 4.13) in areas that CCAMLR is the competent authority
(CCAMLR, 2009). Although the EEZ of the French territories of Kergue-
len and Crozet fall in or partially in the CCAMLR zone, the French
authorities manage the fisheries outside of the CCAMLR framework, and
the reduction in seabird mortality has been considerably slower, with
considerable numbers of birds still killed in the Kerguelen and Crozet
fisheries (Delord et al., 2010). The main species effected are white-chinned
petrels (Procellaria aequinoctialis) and grey petrels (Procellaria cinerea), with
between 7766 and 10,542 birds estimated to have been killed between
September 2003 and August 2006 (Delord et al., 2010). This level of
mortality has now been reduced as some of the CCAMLR mitigation
measures have been adopted (CCAMLR, 2009; Fig. 4.13).
The mitigation measures developed by CCAMLR have gradually been
introduced in national EEZs. In the early days of the Falkland Islands fishery,
large numbers of seabirds were killed, but mitigation has been introduced, and
by 2001, a suite of mitigation was in place and by-catch was reduced (Otley
et al.,2007). However, 134 seabirds were estimated to have been killed in
2003/2004 (Otley et al., 2007). With the introduction of the umbrella system,
correct line-weighting regimes and the use of well-designed streamer lines and
the ‘Brickle Curtain’, seabird mortality was eliminated during the 2007/2008
and 2008/2009 seasons (Brown et al., 2010).
In the Chilean fishery, the introduction of trotlines has dramatically
reduced the number of seabirds killed (Moreno et al., 2006, 2008). In 2002,
1542 birds were killed, compared to zero in 2006. The difference is attributed
to the greater sinking rate of the trotline system, in which the hooks are
clumped with weights. A further problem is that of hook ingestion by
scavenging birds, particularly wandering albatross, which occurs when
hooks are not removed from discarded by-catch and offal (Phillips et al.,
2010). The discarding of baited hooks or of hooks in by-catch species is
prohibited in many fisheries. However the increased use of trotlines has been
implicated as the reason for a recent increase in hooks in wandering albatross
regurgitates (Phillips et al., 2010), with a greater number being cut off and
discarded when they become tangled with the net-sleeves during hauling.
11.6. Interactions with marine mammals
Interactions between marine mammals and fisheries can take the form of
competition for resources, incidental by-catch and depredation of fish from
fishing gear. Incidental mortality is not a significant problem in Patagonian
The Patagonian Toothfish: Biology, Ecology and Fishery 283
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toothfish fisheries, although there have been very occasional reports of
sperm whales drowning following entanglement in Spanish-double line
gear (CCAMLR, 2009). Competition has been considered in the trophic
ecology section, so here, the focus is on the issue of depredation.
Marine mammal depredation of line caught fish is a problem throughout
the world (Visser, 2000; Yano and Dahlheim, 1995) but has become
particularly acute in the high value Patagonian toothfish fishery in recent
years. Depredation by killer whales (Orcinus orca) and sperm whales (Physeter
macrocephalus) was first reported by observers at South Georgia in 1994
(Ashford et al., 1996) but has since been reported in other fisheries (Nolan
et al., 2000), and recent years have seen the problem increase (Ashford et al.,
1996; Kock et al., 2006; Nolan et al., 2000; Purves et al., 2004). Depredation
is apparent from heads and lips that are left on the line by the cetaceans and,
at times, the majority of the catch on a line could be lost to depredation.
Depredation from sperm whales and killer whales are rather different. Killer
whales operate in pods of 3–15 animals, whilst sperm whales are often
solitary. Sperm whales are natural predators of toothfish and can take tooth-
fish from lines at depth, whereas killer whales only dive to 300 m and tend
to strip fish from lines close to the surface (Fig. 4.15).
Quantifying the lost catch is not straightforward. One approach is to
look at catch rates in the presence and absence of both killer and sperm
whales. Since sperm whales are natural predators on toothfish, they tend to
be abundant in areas where toothfish are abundant, and in some areas, there
is no evidence of a reduction in catch rates in the presence of sperm whales
(Brown et al., 2010; Hucke-Gaete et al., 2004; Purves et al., 2004).
Figure 4.15 Killer whale (Orcinus orca) with a Patagonian toothfish (Dissostichus elegi-
noides) depredated from a line. Photo-courtesy of Manuel Sampedro Garcia (FV CFL
Gambler).
284 Martin A. Collins et al.
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However, when killer whales are present, catches can be greatly reduced,
and if the vessel does not stop hauling, whole lines may be stripped.
In Crozet, the CPUE dropped 22% in the presence of killer whales, 12%
in the presence of sperm whales and 42.5% when both were present (Roche
et al., 2007). Overall, the level of depredation at Kerguelen (3%) is consid-
erably lower than at Crozet (33%), which is attributed to the lower abun-
dance of killer whales at Kerguelen (Roche et al., 2007).
Fishing vessels have responded to the cetacean problem in a number of
ways. Fishing with pots prevents both sperm and killer whales from taking the
catch, but pot-catch rates are considerably lower than those of longlines. The
use of net sleeves or cachaloteras is effective against sperm whales; however,
killer whales are learning to bypass the nets and there is evidence of predation
by killer whales on umbrella lines (Brown et al., in press). A common practice
in response to the presence of killer whales is to stop hauling and buoy the line
off, so that the fish are beyond the diving range of the orcas. The vessel will
then move to another location at speed and attempt to lose the killer whales,
or pass them to another vessel. Acoustic deterrents have been used to mediate
the problem of killer whales ( Jefferson et al., 1996; Morton and Symonds,
2002), but whales can quickly become accustomed to such devices.
Antarctic fur seals have also been implicated in depredation at Kerguelen
(Roche et al., 2007) and occasionally at South Georgia. At South Georgia,
depredation by fur seals increased during the 2009 season, when the abun-
dance of Antarctic krill, the primary prey of fur seals, was exceptionally low.
12. Stock Assessment
A number of methods, have been used to carry out stock assessments
for Patagonian toothfish fisheries around the Southern Ocean, the Patago-
nian Shelf and Chilean waters.
Initially, there were insufficient data to assess the fisheries using conven-
tional stock assessment techniques. As Patagonian toothfish are long lived and
slow growing, a reasonable catch and effort dataset combined with a suite of
life history parameters is required for any age or length-based assessment
methods, and it takes several years to build up these datasets. Early attempts
at assessing fisheries used Leslie stock depletion models. Parkes et al. (1996)
used the Leslie depletion model to examine local patterns in CPUE of
toothfish in longline fisheries around South Georgia and off the Pacific coasts
of Chile. They found that 54 out of 107 CPUE series showed a negative
trend with cumulative catch, which was less than would be expected by
chance according to binomial theory; however, only 18 of these datasets
showed a significant negative trend. They concluded that depletion models
were not a suitable method for estimating local abundance, and the authors
The Patagonian Toothfish: Biology, Ecology and Fishery 285
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cited fish behaviour and the actions of fishermen as complicating factors that
made the use of regression models inappropriate. In the same year, des Clers
et al. (1996) applied a modified DeLury depletion model to toothfish CPUE
in the Falkland Islands longline fishery but also failed to produce reliable
results, concluding that the model’s assumptions were not valid and that there
was a likely extensive migratory behaviour in the Patagonian toothfish.
The rapid expansion of the toothfish fishery in the Southern Ocean in the
late 1980s and early 90s was a major concern, which was compounded by the
lack of data for traditional stock assessment methods. Also, adult populations
were inaccessible to trawl surveys and therefore could not be estimated by
traditional swept area methods (Constable et al., 2000). To take into account
this lack of data and the fact that the fishery was already in progress,
CCAMLR developed two approaches for management, a generalised yield
model (GYM) for stock assessment (Constable and de la Mare, 1996)and
regulations restricting the development of new fisheries. The GYM was built
on the approaches already developed for a krill yield model. As data from the
longline fishery were insufficient and fishery independent surveys could not
access the adult population, there was no estimate of initial biomass (B
0
).
These problems were overcome by using absolute estimates of recruits (using
CMIX, de al Mare, 1994) and projecting those forward using simulations.
This allowed for recorded catches to be discounted from the population, and
consequently, a long-term yield could be assessed in tonnes rather than as a
proportion of B
0
. In South Georgia, a relatively large number of bottom trawl
survey data were available allowing the estimation of recruitment of 4-year-
old toothfish. This approach was used to assess the South Georgia stock from
1995 to 2004, when it was replaced by an integrated approach using mark-
recapture data.
Mark and recapture methods have been used to assess toothfish popula-
tion sizes in Macquarie Island (Tuck et al., 2003) and South Georgia (Agnew
et al., 2006a) fisheries. Essentially, exact time of release and recapture data
are used in a stock assessment model that unifies a semi-parametric approach
with the Petersen method. A maximum likelihood approach is used to
estimate the available abundance of toothfish (fishable abundance, which
is different to total or spawning biomass).
An attempt at estimating adult toothfish densities using baited cameras was
conducted by Yau et al.(2001)in the Falkland Islands and South Georgia.
They used an autonomous camera system (see Section 10) and attempted to
calculate toothfish density based on mean first arrival time, as demonstrated by
Priede and Merrett (1996).Yau et al. (2001) data gave estimates of 0.4 and
1.32 toothfish per km
2
for South Georgia and the Falkland Islands, respec-
tively. However, the behaviour of the toothfish differed from other scaveng-
ing species to which the method had previously been applied, leaving
considerable uncertainty about the results.
286 Martin A. Collins et al.
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Since 2004, many of the major fisheries for Dissostichus spp. in the
CCAMLR convention area have used fully integrated age-structured stock
assessments with differing complexities and features that can deal with a large
variety of age- and length-structured data. CASAL (Bull et al., 2005)(Cþþ
algorithmic stock assessment laboratory) is an integrated assessment method
that can be used to implement either an age- or length-structured model, with
options to structure the population by sex, maturity and/or growth path.
CASAL can be used for a single stock or fishery or for multiple stocks, areas
and fishing methods. The data can be taken from a number of different sources,
including catch-at-age or catch-at-size data from commercial fishing, survey
and other biomass indices, survey catch-at-age or catch-at-size data and tag
release and recapture data. Estimations can be by least squares, maximum
likelihood or Bayesian methods. CASAL can generate point estimates of the
parameters of interest and can calculate likelihood or posterior profiles, gen-
erating Bayesian posterior distributions using Monte Carlo Markov chain
methodologies. It can also project stock status into the future using determin-
istic or stochastic recruitment and can generate a number of yield measures
commonly used in stock assessments. CASAL is now used in the assessment of
both the Antarctic (Dunn and Hanchet, 2007; Dunn et al.,2004) and Pata-
gonian (Agnew et al., 2007; Candy and Constable, 2008; Hillary et al., 2006)
toothfish. This method differs from the GYM in that many parameters can be
estimated within the model, including B
0
, rather than having to estimate the
parameters individually.
CCAMLR advocates an ecosystem approach to managing fisheries and
all CCAMLR toothfish assessments are highly precautionary. Within
CASAL, the historic stock dynamics are projected 35 years into the future
under a variety of plausible scenarios. A constant catch projection allows the
calculation of a long–term yield that satisfies the CCAMLR decision rules.
The yield is chosen such that the probability of spawning stock biomass
(SSB) dropping below 20% of its median pre-exploitation level during the
35-year projection is not greater than 10% and that the median escapement
in the SSB at the end of the projection is not less than 50%.
Age-structured production models (ASPMs) have been used for the
assessment of a number of marine resources, including for Patagonian
toothfish stocks. Its first application to toothfish was by Gasiukov and
Dorovskikh (2000). ASPMs have an advantage over biomass-based (aggre-
gated) production models because they allow for a delay in the reduction of
spawning stock biomass (SSB) and thus year class strength as a result of
fishing (Brandao et al., 2002). Brandao et al. (2002) used a simple ASPM for
the assessment of the toothfish resource within the Prince Edward Islands
EEZ, which provided a robust indication that the SSB had been depleted to
a few percent of its original level, and their projections suggested that the
annual TAC should be reduced to 400 tonnes.
The Patagonian Toothfish: Biology, Ecology and Fishery 287
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Payne et al. (2005) used an ASPM based on Brandao et al.’s (2002) work
to assess the Patagonian toothfish population in the Falkland Islands. They
used two models, one with a Beverton-Holt stock recruitment relationship
and another using trawler CPUE to estimate yearly recruitment. The
models were fitted to standardised longliner CPUE and catch-at-length
data. The two models produced estimates showing similar declines in
biomass as the fishery progressed, but the initial and final biomasses varied
slightly between models. The models provided estimates of the current
biomass at between 38% and 46% of its pre-exploitation level and maximum
sustainable yields (MSY) of between 912 and 3000 tonnes. There was a poor
fit to CPUE between 1994 and 1996 which Payne et al. (2005) attributed to
IUU catches or changes in catchability and/or mortality. During this time
(mid 90s), there was considerable IUU activity in the SW Atlantic, and
when their model was adjusted to allow an estimated level of extra catch,
the fit improved and 5000 tonnes of extra catch was estimated. The ASPM
was adapted further by Paya and Brickle (2008) to include updated von
Bertalanffy and natural mortality parameters. Further developments in the
Paya and Brickle (2008) model included a model to allow both longline and
trotline (with cachalotera) CPUE series to be used.
13. Concluding Remarks
The initial rapid development of Patagonian toothfish fisheries in the
Southern Oceans took place without the requisite knowledge of the biol-
ogy of the target species or any assessment of the ecosystem impacts of the
fisheries. Sustainable management of these fisheries has also been hampered
by their remote locations, which have limited both research opportunities
and surveillance. Consequently in many areas stocks were rapidly depleted
and large numbers of seabirds killed. Knowledge of the biology and ecology
of toothfish has expanded considerably in the last decade, with significant
advances in stock discrimination; assessments of population size through
tagging; growth rates and in trophic ecology. Significant gaps still remain in
our knowledge of toothfish. There is still uncertainty about the distribution
of Patagonian toothfish, with many parts of the Southern Ocean remaining
unexplored. Whilst genetic and other studies have revealed segregation of
stocks there are still important questions about linkages between popula-
tions in proximate locations. The larval phase of toothfish is poorly known,
and whilst links between recruitment and oceanography have been identi-
fied the functional relationship is not established. A better knowledge of the
larval phase will be key to understanding the potential consequences of
climate change, since change is more likely to be manifested in surface
temperatures and currents than in the deeper water occupied by adults.
288 Martin A. Collins et al.
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Fisheries have adapted rapidly and methodology radically changed to limit
the negative effects on the ecosystem, but further changes are likely to
counter the depredation problem. Finally, stock assessments will continue
to be refined by increased knowledge of population parameters and
improved estimates of stock size from methods such as tagging. Continued
vigilant management and surveillance is essential for the long-term sustain-
ability of the valuable Patagonian toothfish fisheries.
ACKNOWLEDGEMENTS
This review was stimulated by discussion at the CCAMLR Working Group on Fish Stock
Assessment and benefited from valuable discussions in this forum. In particular the authors
wish to thank recent convenors Inigo Everson, Stuart Hanchet and Chris Jones and
Karl-Hermann Kock for their encouragement. Thanks to Peter Fretwell in the BAS
mapping section for producing Figure 2 and to Jack Fenaughty and Manuel Sampedro
Garcia for allowing us to use their photographs. Thanks to the Falkland Islands Fisheries
Department for supporting this work.
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