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Biological Observations on Shark Species Taken in Commercial Fisheries to the West of Ireland



During an investigation into the biology of three shark species commonly taken in Irish fisheries, biological information was also collected from an additional six less-common species: Galeorhinus galeus, Lamna nasus, Mustelus asterias, Galeus melastomus, Hexanchus griseus and Dalatias licha. Data on age, reproduction, feeding and parasites were collected from a total of 137 sharks. Age data from G. galeus and M. asterias suggest possible differences in growth-rate relative to other areas. The state-of-maturity of all specimens agreed with earlier studies, although data regarding the reproductive cycle of M. asterias and G. melastomus were inconsistent with data commonly reported for these species. Stomach contents were unremarkable, with the exception of 1.3kg of cetacean material recovered from a specimen of H. griseus. Results from the parasite component of the investigation extend the known range of two monogenean species, while a further three parasites were recorded from new hosts.
A.C. Henderson, K. Flannery and J. Dunne
During an investigation into the biology of three shark species commonly taken in Irish fisheries,
biological information was also collected from an additional six less-common species: Galeorhinus
galeus,Lamna nasus,Mustelus asterias,Galeus melastomus,Hexanchus griseus and Dalatias licha. Data on
age, reproduction, feeding and parasites were collected from a total of 137 sharks. Age data from
G.galeus and M.asterias suggest possible differences in growth-rate relative to other areas. The
state-of-maturity of all specimens agreed with earlier studies, although data regarding the
reproductive cycle of M.asterias and G.melastomus were inconsistent with data commonly reported
for these species. Stomach contents were unremarkable, with the exception of 1.3kg of cetacean
material recovered from a specimen of H.griseus. Results from the parasite component of the
investigation extend the known range of two monogenean species, while a further three parasites
were recorded from new hosts.
A.C. Henderson
(corresponding author;
Department of Marine
Science and Fisheries,
Sultan Qaboos
University, P.O. Box 34,
Al-Khod 123, Oman; K.
Flannery, Department of
the Marine and Natural
Resources, Dingle, Co.
Kerry; J. Dunne,
Department of Zoology,
National University of
Ireland, Galway.
Received 3 November
2000. Read 16 March
2002. Published 31
July 2003.
The Irish fishing fleet is diverse, ranging from
inshore and deep-water trawlers to pelagic and
bottom-set gill-netters. With most marine habitats
targeted, it is not surprising that a wide range of
shark species is regularly taken. However, since the
collapse of the basking shark fishery on the west
coast, directed fisheries are few, although certain
species remain valuable by-catch.
Despite increasing fishing pressure, relatively
little biological work has been conducted on sharks
in these waters, and our understanding of their
biology and stock divisions is limited. With this in
mind, the Department of Zoology at National
University of Ireland, Galway, developed a
research programme in 1996. The aim of this
programme was to collect biological information
from commercially caught/landed sharks, paying
particular attention to those species that are taken
in greatest numbers in pelagic and inshore fisheries,
i.e. blue shark, Prionace glauca L., spiny dogfish
Squalus acanthias, and lesser-spotted dogfish,
Scyliorhinus canicula L. While information collected
from these species has been reported previously
(Henderson et al. 2001; Henderson et al., 2002a;
2002b; 2002c; Henderson and Casey, 2001), the
aim of this work is to report biological information
collected from other species. The data collected
were typically concerned with age, reproductive
biology, feeding and parasitology. The species
examined were tope, Galeorhinus galeus (L.);
porbeagle, Lamna nasus (Bonnaterre); starry smooth
hound, Mustelus asterias Cloquet; blackmouth
dogfish, Galeus melastomus Rafinesque; six-gill
shark, Hexanchus griseus (Bonnaterre); and kitefin
shark, Dalatias licha (Bonnaterre).
Specimens examined were landed by the Dingle
fishing fleet throughout 1998. Sampling was
necessarily opportunistic; in addition to examining
commercially landed specimens, fishermen were
asked to retain (when possible) those shark species
which would normally be discarded. Such
specimens were held on ice while at sea, and
examined immediately upon landing. With the
exception of H.griseus,D.licha, and G.melastomus
(which were taken in deep-water trawls in the
region of the Porcupine Bank), all specimens were
captured in bottom-set gill-nets in the shelf-waters
west of Ireland. Commercially important species
such as porbeagle and tope were commonly landed
gutted, and data collection in such cases was
therefore limited to size and external parasites.
Pre-caudal length (PL), fork length (FL), and
total length (TL) of each specimen were measured
to the nearest centimetre. In the case of porbeagle,
very little time was available for examination
and, in many cases, only PL was measured.
Nonetheless, all length measurements reported
. 103B, N
. 1, 1– 7 (2003). © R
should be read as TL unless otherwise indicated.
Information collected on reproductive biology
consisted of gonad weight/fecundity and
oviducal-gland width /clasper length. The gills
and body surface were examined for parasites, and
the alimentary tract was examined for food remains
and parasites (see Henderson et al. 2002b for
Vertebral centra were used for age estimation
(Cailliet et al. 1986), except in six-gill and kiten
sharks, where vertebrae were too poorly calcied
to use. Vertebrae were cleaned in a trypsin
solution, which was kept at 37°C for up to 48
hours. Porbeagle vertebrae were stained in a
solution of alizarin red S (LaMarca 1966) for
approximately ve minutes, and examined under a
binocular microscope. Smooth hound vertebrae
were stained in the same manner although, due to
their relatively deep-coned nature, half of the
vertebra was rst ground away (along the
anterior-posterior axis). Tope vertebrae required
more processing, as follows:
1. Using the coarse wheel on a bench grinder, the
vertebra was ground down to within 2.0mm of
the focus, after which the ne wheel was used
to continue grinding until the focus was
2. The ground face was polished on ne grain
(P600) wet sandpaper, and the vertebra was
glued to a glass slide (ground face down) using
araldite resin.
3. The resin was allowed to set for 48 hours, and
the remaining half of the vertebra was ground
(as above) until only a thin section of the
vertebra remained on the slide.
4. This was again polished on ne grain wet
sandpaper, rinsed in water, and immersed in an
alizarin red staining solution (see above) for
about ve minutes.
5. The slide was examined under a low power
(×20) binocular microscope.
The solitary specimen of blackmouth dogsh
was aged using the acid decalcication technique
of Correia and Figueiredo (1997).
A range of biological data recorded from individual
sharks of ve of the species is presented in Table 1.
Nineteen male and three female tope were
examined. They ranged in length from 70162cm.
Vertebrae were collected from four individuals,
and the estimated age ranged from 1012 years
(see Table 1). Of the three female tope examined,
one still had its reproductive tract in situ (despite
being gutted), and this 132cm individual was
completely immature. Testis weights were
available from four individuals and clasper length
was measured in all nineteen males (Table 1).
Seven alimentary tracts were examined, all of
which contained teleost remains. However, no
identication of prey was possible due to the
advanced state of digestion of the prey. Beaks from
two specimens of octopus, Eledone cirrhosa
(Lamarck), were also recorded from one indi-
A total of six parasite species were recorded,
the most common being the nematode Anisakis
simplex L
Rudolphi, which was recorded in four
of the seven sharks examined. In most instances
this parasite was recorded from the stomach lumen,
but in one shark it was also found in the spiral
valve. The intensity of infection ranged from
153. One of the sharks harbouring this nematode
was also infected with two specimens of
Hysterothylacium aduncum L
(Rudolphi), which
were also found in the stomach. The only other
intestinal parasite recorded was the cestode
Anthobothrium cornucopia van Beneden, which was
found in the spiral valve of three sharks. Two
copepod species were recorded. A single specimen
of the more common of these, Pandaras bicolor
Leach, was attached to the respective anks of two
sharks, while a third shark had two specimens
attached to the ventral surface of its left pelvic n.
Lernaeopoda galei Kroyer, was found attached to the
cloacal region of one shark. The monogenean
Erpocotyle canis (Cerfontaine) was the only gill
parasite recorded. A total of four of these parasites
occurred on one of the sharks examined.
Data were collected from a total of 91 porbeagle
sharks, although the viscera and vertebrae of only
one of these sharks were available for examination.
The size distribution is presented in Fig. 1. Of the
nineteen females examined, only one individual
had its reproductive tract still in place, and this
170cm female was completely immature. The
distribution of clasper lengths for 72 males is
presented in Fig. 2.
The stomach contents of the single individual
examined (one year old, 100cm TL) yielded the
remains of many euphausiids (16g) and four
polychaete worms (7.2g). Both prey types were
highly digested, and no further identication was
possible. This individual and a further thirteen
porbeagle were examined for external (skin)
parasites. Of these, two were also examined for
gill parasites. Two specimens of the copepod
Dinemoura producta (Mu¨ller) were recorded from
the pelvic n of a 122cm female, and a further six
specimens of this copepod were aggregated on the
Table 1—Biological data recorded from sharks taken in commercial fisheries west of Ireland.
Species Sex Length
Estimated age Clasper/nidamental
Gonad weight
G.galeus M 139 16
F 119
M 140 16
M 151 14
F 132 0.5
M70 4
M 152 15 185
M 161 14.5
M 147 15
M 156 15
M 151 14
M 152 16
M 141 15
M 162 15
M 103 7 103
M 133 15
M 141 10 14 123
M 148 12 15
M 149 10 14.5 80
M 152 11 15 185
M 162 15
H.griseus M 93 3.4 0
M 122 6 0
F 165 1 0
M79 4 0
F66 0 0
F92 0 0
F 86 0.5 0
M 101 5.2 0
M84 0 0
F 98 0.8 1
M 86 3.5 0
F85 0 0
M.asterias F 87 6 2.7 27
F 89 6 3.2 59
F 109 8 2.8 13
D.licha M 45 1.6 0
M 45 1.8 0.2
M 42 1.75 0
F39 0 0
F51 0 0
F40 0 0
F45 0 0
F42 0 0
F44 0 0
G.melastomus F 67 6 2.0 30
dorsal surface of the left pelvic n of a 250cm
female. One specimen of the isopod Natatolana
borealis (Lilljeborg) was found attached to the roof
of the mouth of a 233cm female, although it is most
likely that this was a post-mortem occurrence.
A total of three female smooth hounds was
examined (Table 1). All three individuals had
encapsulated eggs in their uteri. The fact that
embryos were not yet visible to the naked eye seems
to imply that encapsulation had occurred relatively
recently. Table 2 presents the number of eggs and
oocytes recorded from the three specimens. The
87cm specimen had remains of crustacean material
in its stomach, but they were too fragmented for
identication. The 89cm specimen contained one
squat lobster, Galathia squamifera Leach (6.1g), and
the remains of a swimming crab, Liocarcinus depurator
(L.) (3.0g).
Four parasite species were recorded. Two
smooth hounds were infected with an
indeterminate species of the nematode Proleptus:
two were found in the stomach lumen of the 89cm
specimen and three in that of the 109cm specimen.
An indeterminate species of the cestode
Anthobothrium was the only other intestinal parasite
recorded. Four of these parasites were recovered
from the spiral valve of the 87cm specimen and two
from the spiral valve of the 109cm specimen. Two
species of gill parasite were recorded: the copepod
Kroyeria lineata van Beneden, and the monogenean
Erpocotyle laevis Beneden and Hesse. A single
specimen of the latter was recorded from the 109cm
specimen, while nine E.laevis specimens and one of
K.lineata were recorded from the 89cm and 109cm
specimens respectively. The specimens of K.lineata
recovered are of interest in that their form is much
smaller and highly transparent compared with
specimens recovered from blue sharks (Henderson
et al. 2002c).
Fig. 1Size distribution of porbeagle sharks (Lamna nasus) taken in bottom-set
gill-nets in shelf-waters to the west of Ireland. The 90cm length-class indicates a
range of 9099cm, the 100cm length-class indicates a range of 100109cm, etc.
Table 2Numbers of encapsulated eggs and
oocytes recorded from Mustelus
asterias. Multiple values indicate
distinct size classes.
meanTotal Encapsulated
eggslength diameter
10109 9 (1.6cm)+4 (1.2cm)
87 10 1 (1.3cm)+2 (1.0cm)
10 (1.5cm)289
Fig. 2Clasper lengths recorded from porbeagle sharks, Lamna nasus.
The estimated age and measurements recorded from
this single individual are presented in Table 1.
Unfortunately, the ovary did not preserve well, and
no measurements could be taken. The uteri
contained ve fully-formed egg-cases. The only
parasite recorded was the copepod Eudactylina similis
(T. Scott), four specimens being recovered from the
gills. No food items were recorded.
The only food recovered from the six-gill sharks
was 1.3kg of cetacean material found in the stomach
of the 165cm specimen. Four of the eight kiten
sharks contained digested teleost material, while
three contained crustacean remains. However, the
material was digested beyond identication.
Three species of parasite were recorded from
the twelve six-gill sharks examined: the nematode
A.simplex L
and the cestodes Phyllobothrium dohrni
(Oerley) and P.sinuosiceps Williams. Anisakis
simplex L
was recorded from three sharks,
occurring in the stomach and spiral valve and
encysted in the stomach wall. Individual cestodes
were recovered from the anterior of the spiral
valve in each of three sharks.
Two kiten sharks contained nematodes in
the stomach lumen but all three parasites were in
poor condition. While it appears that there may
have been three separate species, only one could
be identied, i.e. A.simplex L
. One of the
remaining nematodes also appeared to be a larval
anisakid (a larval tooth was evident): based on the
morphology of the head it may have possibly been
a species of Raphidascaris.
As discussed by Francis and Mulligan (1998),
growth rates in tope (G.galeus) from various parts
of the world seem to vary, a problem compounded
by the use of different ageing techniques in studies.
Sectioned centra were employed during the
present study, which greatly increased the clarity of
distal growth bands when compared with whole
stained centra (A.C. Henderson, pers. obs.), so it
seems unlikely that the present specimens were
under-aged to the degree that they were by
Moulton et al. (1992), as reported by Francis and
Mulligan (1998). The present study showed larger
sizes at age than studies of tope from southern
Brazil (Ferreira and Vooren 1991) and from New
Zealand waters (Francis and Mulligan 1998): if,
indeed, age determination was accurate during the
present study, the larger sizes at age indicate that
tope may display a faster growth rate in the
north-eastern Atlantic than in other areas.
Capape´and Mellinger (1998) report that the
reproductive organs of female tope display
increased development from 100cm onwards. It is
therefore surprising that the reproductive tract
of the 132cm individual examined appeared
immature. Tope are known to commonly prey on
sh (as found here) and cephalopods (Whitehead et
al. 1989), and the octopus E.cirrhosa found in this
study has been previously recorded from this shark
in the north-eastern Atlantic (Ellis et al. 1996).
According to Compagno (1984), the size at
birth of the porbeagle, Lamna nasus,is6075cm,
with specimens in the north-eastern Atlantic
attaining sizes up to 300cm (Gauld 1989). The
determination that the 100cm specimen was one
year old is in close agreement with Aasen (1963)
for porbeagles in the north-western Atlantic.
Unfortunately, no comparable data exist for the
north-eastern Atlantic. Females do not mature
until at least 200cm (Aasen 1961), as was also
found here. Relative clasper lengths are similar to
those recorded by Aasen (1961), which indicates
that size at maturity is similar to elsewhere in the
North Atlantic. Few published data exist on the
biology of the porbeagle, but it is known to
commonly prey on a wide variety of small
schooling shes, as well as squid (Compagno 1984;
Vas 1991). The specimen in the present study is
unusual in that it contained only crustacean and
annelid material, although it is possible that small
invertebrates are more important in the diet of
younger porbeagle. The occurrence of annelid
worms indicates bottom feeding, evidence of
which was also found by Gauld (1989).
From the age determination for the smooth
hounds examined during the present study, the
growth rate of this species may be slower than
previously thought. Francis (1981) calculated a
growth coefcient, K, for this species using
existing data on the length of the gestation period,
the size at birth, and the maximum observed
sizea technique rst proposed by Holden
(1974). However the growth bands observed here
indicate this approach may have resulted in an
overestimate of K, and the age at size is almost
twice that predicted in the Von Bertalanffy
equation proposed by Francis (1981).
The gestation period of this species is reported
as twelve months by Compagno (1984), with
parturition occurring in summer (Kennedy 1969;
Wheeler 1969; Compagno 1984). This in-
formation implies that ovulation must also take
place in summer, so it is therefore surprising that
the three specimens examined during the present
study all contained recently fertilised ova. Without
knowing the spermatozoa-storing capabilities of
the oviducal-gland of the species, little can be
inferred as to when mating occurs. However, the
present results clearly indicate that the breeding
season begins as early as spring. The number of
fertilised ova in the uteri of the 87cm and 109cm
specimens falls within the fecundity range reported
for the species (Compagno 1984; Vas 1991);
however, the number of fertilised ova in the uteri
of the 89cm specimen is very low. In all three
specimens, the size of the oocytes indicates that
ovulation for the present season was complete,
which would suggest that fertilised ova were
possibly aborted during capture. Smooth hounds
feed primarily on crustaceans and invertebrates
(Compagno 1984), and both Galathia and
Liocarcinus have been previously recorded from
smooth hounds in the north-eastern Atlantic (Ellis
et al. 1996).
The estimated age of the blackmouth dogsh
agrees with results obtained by Correia and
Figueiredo (1997) for specimens in Portuguese
waters. Little information exists on the
reproductive biology of this shark, but Compagno
(1984) noted that females mature between 39cm
and 45cm and may have up to thirteen eggs
present in the oviducts. The current specimen may
therefore not yet have formed a full complement
of egg-cases. Wheeler (1969) notes that egg-cases
ready for extrusion are abundant off the
south-western coast of Ireland in early July.
However, the current specimen was captured in
spring, indicating that either egg-laying may begin
earlier in the year than previously thought or the
process of forming a full complement of egg-cases
may take a considerable amount of time.
The virtual absence of gonad tissue from the
six-gill and kiten sharks is indicative of wholly
immature animals: this agrees with Berrows
statement that the majority of six-gill sharks taken
in Irish waters are immature (Berrow 1994a). The
six-gill shark is commonly reported as being
mainly piscivorous (Compagno 1984; Vas 1991).
However, Ebert (1994) also recorded mammalian
remains from six-gill sharks off southern Africa,
indicating that mammals may also be important
prey. The scientic literature reports that the
kiten shark is mostly piscivorous (Wheeler 1969;
Whitehead et al. 1989), but Compagno (1984) and
Vas (1991) have also reported crustacean material
from this species.
Many of the parasites recorded here are
commonly recorded from their respective hosts
(see Yamaguti 1959, 1961; Williams 1960; Scott
1963; ORiordan 1966). However, certain species
are of interest. The occurrence of the nematode A.
simplex L
in H.griseus appears to be a new host
record, at least for the north-eastern Atlantic.
Similarly, this parasite has not been previously
reported from any of the other species for which it
was recorded here. Additional host records are K.
lineata on M.asterias, and E.similis on G.
melastomus. The latter record is also interesting
because it is the rst occurrence of this parasite on
a non-rajid host.
Dawes (1947) reported the occurrence of E.
laevis on M.asterias from Plymouth, but apart from
occurring on this host elsewhere on the south coast
of England (A.C. Henderson, pers. obs.), there are
no further records around Britain and Ireland. The
current record therefore extends the known range
of this parasite. This is also the case for its tope
parasitising congener E.canis, which has hitherto
not been reported anywhere in British or Irish
waters, the most northerly record being that for
the French and Belgian coasts (Dawes 1947). The
occurrence of the isopod N.borealis is also
interesting. This species is generally regarded as a
scavenger, feeding on both dead and dying sh,
particularly those trapped in nets (Keable and
Bruce 1997). Berrow (1994b) recorded N.borealis
feeding on a variety of sh caught in bottom-set
gill-nets off the Irish coast, including some shark
species, but the present record appears to be the
rst instance involving L.nasus.
The authors would like to thank the Dingle shing
eet for providing specimens, and also the
management and staff of OCathain Iasc Teo for
allowing examination of their landings. We would
also like to thank Dingle Oceanworld for
providing dissection facilities. The expertise of
Mark Holmes (Natural History Museum, Dublin)
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The subvention granted
by the National
University of Ireland,
Galway, towards the
cost of publication of
papers by members of
its staff is gratefully
acknowledged by the
Royal Irish Academy.
... Despite reliable catch data, information about life history of G. galeus is also lacking. Growth studies have been undertaken for G. galeus stocks elsewhere (Grant et al., 1979;Ferreira & Vooren, 1991;Moulton et al., 1992;Francis & Mulligan, 1998;McCord, 2005), but to date, only one study has examined age structure of this stock based on vertebral samples of four males (Henderson et al., 2003). Therefore, the aim of this study was to determine growth parameters of G. galeus in the north-east Atlantic Ocean. ...
... Obtaining growth estimates from mark-recapture data can be particularly important for species such as G. galeus, where vertebral readings may not represent an adequate procedure to estimate age (Kalish & Johnston, 2001). The results of this study were compared with the only available age data of G. galeus in the north-east Atlantic Ocean, obtained from vertebrae (Henderson et al., 2003). Their preliminary age estimates of four male specimens with a L T of 141, 148, 149 and 152 cm were 10, 12, 10 and 11 years, respectively. ...
... The estimates would suggest ages of 17, 20, 21 and 22 years for the same L T . Hence, the estimated ages from the growth parameters obtained in this study were up to 50% higher than to those reported by Henderson et al. (2003), which would support previous concerns that vertebral readings can underestimate age in this species (Officer et al., 1996;Kalish & Johnston, 2001). The presented method selection procedure can aid in obtaining less biased growth parameters from mark-recapture tagging data by finding the best performing method for a given data set, especially if the sample size is small. ...
This study addresses the inherent uncertainty when estimating growth from limited mark–recapture information. A selection procedure was developed utilizing 18 competing growth estimation methods. The optimal method for a given data set was identified by simulating the length at capture and recapture under different scenarios of measurement error and growth variability while considering the structure of observed data. This selection procedure was applied to mark–recapture data for 37 female and 16 male tope sharks Galeorhinus galeus obtained from tagging studies in the north-east Atlantic Ocean. Parameter estimates differed strongly among methods, showing the need for careful method selection. The selection approach suggested that best estimates for males and females were given by James' weighted least-squares approach with a fixed asymptote. Given an average total length (LT) at birth of 28 cm, the von Bertalanffy growth function of north-east Atlantic G. galeus would be LT = 200·85 − (200·85 − 28)e− 0·076t for females and LT = 177·30 − (177·30 − 28)e− 0·081t for males. The resulting age estimates were up to 11 years lower when compared with previous estimates derived from highly uncertain vertebrae readings. More generally, this procedure can help identify optimal estimation methods for a given data set and therefore aid in estimating more reliable growth parameters from mark–recapture information.
... Although only mature species were recorded from the Azores demersal longlines, a wider length range including immature individuals was recorded more broadly in the North Atlantic Ocean from trawl fisheries off Ireland and Scotland (Henderson et al. 2003, Neat et al. 2015, to the south off the coast of West and South Africa (Bass et al. 1976, Pascual-Alayon et al. 2017, and in the Mediterranean Sea (e.g., Capapé et al. 2008). In these areas, the sex ratio was varied with more females than males reported off Scotland, but males were more commonly caught in the south-western Mediterranean, giving some indication of segregation, at least by sex. ...
Technical Report
Vector Autoregressive Spatio-Temporal (VAST) models were applied to research trawl survey and environmental data to provide updated information on stock status for seven deepwater sharks. Deepwater sharks were found to be ubiquitous around New Zealand, with each species shown to have a unique distributional pattern. Deepwater shark “hotspots” in New Zealand waters were identified (e.g., Puysegur). There was little evidence to suggest any temporal or spatial changes in distribution or abundance.
... Previously, Bird (1981) reported this species on sharks from Atlantic coastal waters off Florida and Henderson et al. (2003) on Lamna nasus (Bonnaterre, 1788) in the west of Ireland waters. Therefore, we believe that it is the first record of N. borealis on M. mustelus, M. punctulatus and S. canicula. ...
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Between 2015 and 2018, a total of 1656 fish specimens belonging to four elasmobranch species was collected from the Tunisian coast and examined for isopods. Two species of Cirolanidae, Natatolana borealis and Natatolana neglecta, are reported for the first time from the Tunisian coast. This study presents new data on the morphology, distribution and behaviour of the two species. This is the first record of Natatolana borealis on Mustelus mustelus, Mustelus punctulatus and Scyliorhinus canicula, and of Natatolana neglecta on the elasmobranch Raja clavata. The scavenging behaviour of N. borealis and N. neglecta on elasmobranchs showed that these two species present similar behaviour. We also noted that their impact on fisheries in the first hours of infestation was negligible as the infested fish specimens did not show any external or internal damages. Résumé : Morphologie et comportement de charognards de deux espèces du genre Natatolana (Crustacea : Isopoda : Cirolanidae) attaquant les élasmobranches des côtes tunisiennes. Entre 2015 et 2018, un total de 1656 spécimens de poissons appartenant à quatre espèces d'élasmobranches a été récolté sur la côte tunisienne et examiné pour rechercher des isopodes. Deux espèces de Cirolanidae, Natatolana borealis et Natatolana neglecta, sont signalées pour la première fois sur les côtes tunisiennes. Cette étude présente de nouvelles données sur la morphologie, la distribution et le comportement de ces deux espèces. En effet, c'est la première mention de Natatolana borealis sur Mustelus mustelus, Mustelus punctulatus et Scyliorhinus canicula. Il s'agit également de la première mention de Natatolana neglecta sur une espèce d'élasmobranche, Raja clavata. De surcroît, nous avons pu déterminer que ces deux espèces d'isopodes présentent un comportement similaire. En outre, nous avons constaté que les spécimens de poissons infestés ne présentaient aucun dommage externe ou interne, prouvant ainsi que l'impact de ces isopodes durant les premières heures d'infestation était négligeable.
... Other reports have estimated a much smaller birth size of 30 cm (Bigelow & Schroeder 1948), with free-swimming specimens reported from as small as 32 cm in the western Mediterranean (Capapé et al. 2008), 36 cm off Southern Africa (Bass et al. 1976), and 39-46 cm off the west coast of Ireland (Henderson et al. 2003) and Scotland (Neat et al. 2015). ...
... Lernaeopoda galei was found on three hosts (Mustelus mustelus, M. punctulatus and Raja clavata). It is a common parasite of elasmobranchs and has been reported from several host species (Raibaut et al., 1998;Henderson et al., 2003;Dippenaar, 2004;Karaytug et al., 2004;Gaevskaya, 2012), although it seems to display a preference for Triakidae since it was reported by Raibaut et al. M. mustelus and by Raibaut et al. (1998) from M. punctulatus. ...
Between 2013 and 2015, 2092 chondrichthyan fish belonging to eight species were collected along the Tunisian coast and examined for parasitic copepods. Eleven different species of copepods representing five families, Caligidae, Eudactylinidae, Kroyeriidae, Lernaeopodidae and Pandaridae, were collected. Three of these species are reported for the first time in Tunisia ( Pseudocharopinus malleus , Perissopus dentatus and Nesippus orientalis ) and one new species of Kroyeria was found. In addition, we identified a number of new host records including: the presence of Eudactylinella alba on Bathytoshia centroura , Dasyatis pastinaca , Mustelus mustelus and Scyliorhinus canicula . This is the first record of Nemesis sp. on B. centroura in Tunisia. We report here for the first time the presence of Pseudocharopinus bicaudatus and Pseudocharopinus concavus on Bathytoshia centroura and Lernaeopoda galei on Raja clavata .
... Near-term embryos have been documented at 680-736mm TL off California (Ebert 1986) and free-swimming neonates at 610-930mm TL off southern Africa (Ebert 2002) and 556-680mm TL in the Mediterranean (Capapé et al. 2004). Henderson et al. (2003) reported on small numbers of H. griseus taken off Ireland, all of which were immature, including a free-living individual of 660mm TL. ...
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Aim: To apply dual-source multidetector computed tomography (DSCT) scanning technology in conjunction with computationally assisted segmentation in order to explore and document skeletal variation that has occurred over the course of evolution. Methods: We examined 4 divergent species of elasmobranchs with high-resolution 3(rd) generation DSCT. The formalin prepared species examined were: Aptychotrema vincentiana, Mitsukurina owstoni, Negaprion brevirostris and Dactylobatus armatus. Results: All three structures of the hyoid arch (hyomandibular, ceratohyal, and basihyal) were clearly visible whereas in the two batoids, the hyomandibular was the prominent feature, the ceratohyal was not visible and the basihyal was more reduced and closer to the gill arches. The general shape of the puboischiadic bar, or pelvic girdle, illustrated a closer relationship between the two sharks and the two batoids than between the two groups. Conclusion: In exquisite detail, DSCT imaging revealed important morphological variations in various common structures in the four elasmobranch specimens studied, providing insights into their evolutionary diversification.
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The starry smooth-hound Mustelus asterias is a near-threatened coastal shark in Europe, whose parasitofauna is largely unknown. We studied metazoan parasites of 20 immature sharks (13 males and seven females) from the English Channel and we examined their relationships with host condition and their use as host bioindicators. All the sharks were parasitized by one to six metazoan taxa among the twelve recorded in the whole sampling (one trematode, six cestodes and two nematodes trophically-transmitted; one monogenean, one copepod and one myxosporean on gills), with a mean abundance of 30.5 ± 21.4 parasites per fish (myxosporeans not included). The three major taxa were in decreasing order: the nematode Acanthocheilus rotundatus (prevalence: 75%, Confidence Interval 53–89%), the cestode Eutetrarhynchus sp. (70%, CI 48–85%), and the monogenean Erpocotyle laevis (60%, CI 39–78%). The gill copepod Kroyeria lineata and the gut nematode Proleptus obtusus were identified as significant pathogens. Parasite community differed between males and females despite their immature stage, suggesting early spatial sex-segregation, with E. laevis , Eutetrarhynchus sp. and Anthobothrium sp. proposed as tags. We discuss results in terms of host fitness loss and information given by parasites on diet ecology and stock discrimination. We recommend incorporating parasitology in further research to improve shark conservation and management.
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Between 2018 and 2020, 696 fish belonging to two species of sharks from the Family Triakidae (Mustelus mustelus and M. punctulatus) were collected from the coasts of Tunisia and inspected for parasites. Six copepod taxa (Perissopus dentatus Steenstrup & Lütken, 1861, Eudactylinella alba Wilson, 1932, Kroyeria lineata Van Beneden, 1853, Nesippus orientalis Heller, 1865 and Lernaeopoda galei Krøyer, 1837, Kroyeria sp.), four isopod species (Anilocra physodes (Linnaeus, 1758), Emetha audouini (H. Milne Edwards, 1840), Ceratothoa parallela (Otto, 1828) and Ceratothoa oestroides (Risso, 1816)) and two monogenean species (Erpocotyle sp1. And Erpocotyle sp2) were collected. A large number of global host records was reported, including the occurrence of E. audouini on M. mustelus and of Erpocotyle sp.2 on M. punctulatus. The study of the diversity of parasites per host species revealed that M. mustelus had a higher parasitic richness compared to M. punctulatus. In this study, it was provided for the first records on ectoparasites on Triakidae sharks from Tunisian coasts and their infection indices.
The reproductive biology and other life-history parameters were investigated for Mustelus asterias in British waters, with specimens caught from both commercial fisheries and research-vessel surveys. In total, 504 specimens [238 males, 24–99 cm total length (LT) and 266 females, 28–124 cm LT] were examined, with further information collected from 238 uterine pups. The lengths at 50% maturity were estimated as 70·4 and 81·9 cm LT for males and females, respectively. Ovarian fecundity ranged from one to 28, and uterine fecundity from four to 20. The number, mass and LT of pups were positively correlated with maternal LT. Full-term pups ranged from 205 to 329 mm LT, and the smallest free-living fish caught was 24 cm LT. Parturition occurred in February in the western English Channel and during June to July in the eastern English Channel and southern North Sea, indicating either protracted spawning or asynchronous parturition for the stock as a whole. The reproductive cycle is thought to extend beyond 1 year. Developmental abnormalities observed included atresia in oocytes, uterine eggs that failed to develop, a partly developed pup and an abnormal male with a single aberrant clasper. Data relating to conversion factors, oocyte numbers and diameter and gonado-somatic and hepato-somatic indices are presented, and the seasonality of the reproductive cycle is discussed.
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The sixgill shark Hexanchus griseus is a large, active, deep-water species that typically occurs along the outer continental shelves and their upper slopes. Stomach analysis was performed on 137 specimens collected off Namibia and South Africa. The major prey groups were cephalopods, teleosts, chondrichthyans and marine mammals. Dietary changes of sixgill sharks are related to growth. In most of their area of distribution, sixgill sharks have few comparable competitors, because sympatric squaloids and lamnoids of equivalent size feed at a lower trophic level.
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The reproductive biology and von Bertalanffy growth parameters were investigated in lesser-spotted dogfish from the west coast of Ireland. The length at 50% maturity was similar for both sexes, occurring at 57.5 cm in males and at 58.1 cm in females. Age at maturity was estimated as six years. The number of oocytes displayed a marked seasonal cycle, which was lowest in March, and highest in November. Observations on maximum oocyte diameter indicate that ovulation occurs at 1.7 - 1.8 cm, and oocytes of this diameter were recorded throughout the study. Additionally, females with egg-cases in utero were also observed throughout the year, indicating a protracted breeding season, although peak egg-laying occurred in May, and was minimal in October. Gonad indices indicated that the male and female gonadal cycles were not synchronous, supporting the idea that females store spermatozoa. Based on this and previous studies, it appears that there are geographical variations in certain aspects of the reproductive biology. Vertebral bands were enhanced using an acid decalcification technique, and for the purpose of the study, bands were assumed to be annual in nature. The von Bertalanffy equation was estimated as lt = 82.7(1-e-0.15(t+1.36), and was similar to a length-frequency generated equation calculated for dogfish in Spanish waters.
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The von Bertlanffy growth curves of male and female gummy shark were significantly different, but the growth curves of male and female school shark were not. Growth rates of male and female gummy shark in Bass Strait were lower during 1986-87 than during 1973-76. Growth rates of male and female gummy shark and school shark in Bass Strait during 1986-87 were lower than those in South Australia at the same time. The growth curves determined for 1986-87 are apparently distorted by the effects of a long history of high and length-selective fishing mortality, and actual growth patterns of gummy shark are better represented by the von Bertalanffy growth equation determined for shark caught in Bass Strait during 1973-76, when fishing mortality was much lower. -from Authors
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The present study was undertaken to examine the parasite fauna of spiny dogfish, and to determine seasonal variations in infection rates and faunal composition. A total of 10 metazoan parasite species was recorded, of which four species occurred in the intestine, three species were parasitic on the gills, two species occurred on the skin, and one species parasitized the spiracle. However, a cumulative parasite species richness curve indicated that a larger sample may have yielded additional parasite species. The parasite assemblage consisted of five species of copepods (Eudactylina acanthii Scott, Caligus curtis Müller, Pandarus bicolor Leach, Echthrogaleus coleoptratus (Guerin-Meneville) and Pseudocharopinus bicaudatus (Krøyer)), two species of nematodes (Anisakis simplex Rudolphi and Hysterothylacium aduncum (Rudolphi)), two species of cestodes (Trilocularia gracilis Olssen and Gilguina squali (Fabricius)), and one species of monogenean (Erpocotyle abbreviata (Olssen)). The parasite fauna was found to be similar to that of S. acanthias from the North Sea, and from New Zealand waters. Results obtained during the present study indicate that the infection rates of certain parasite species display seasonal cycles, most species displaying their greatest prevalence in spring and their lowest prevalence in autumn.
The parameters of the von Bertalanffy growth model are estimated for seven species of Mustelus by extrapolation from embryonic growth rates. The method, developed by Holden (1974), requires information on maximum observed length, gestation period and size at birth. Each of the seven species of Mustelus whose reproductive biology has been studied has a gestation period of 10-13 months. Estimated von Bertalanffy growth constants range from 0.22 to 0.53 for males and 0.21 to 0.36 for females. Sexual maturity is attained 1-4 years after birth. The results obtained using Holden's method are suitable for rapid preliminary estimation of growth rates for purposes of fishery management.