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Multiple paternity in captive grey nurse sharks (Carcharias taurus): Implications for the captive breeding of this critically endangered species

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The grey nurse shark (Carcharius taurus) is listed as threatened throughout much of its global distribution, and as critically endangered in eastern Australia. Captive breeding programs have thus far been largely unsuccessful and little is known of their mating system in this context. Here we carry out a paternity analysis to determine if the mating system in captivity is characterized by multiple mating, and whether poor offspring survival is associated with a particular male. Tissue samples from grey nurse sharks were collected from three potential sires, the two dams and nine pups housed at Manly SEA LIFE Sanctuary in eastern Australia. Each individual was genotyped at seven microsatellite markers and three cases of multiple paternity were inferred. No paternal link to stillborn (5), or scoliotic (2) pups was indicated. For the first time, we show the natural wild phenomenon of multiple paternity occurring in a captive environment.
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Multiple paternity in captive grey nurse sharks (Carcharias taurus): implications for the
captive breeding of this critically endangered species.
Robert Townsend1,2, Adam Stow2 , Maria Asmyhr2, and Paolo Momigliano2,3*
1 Manly SEA LIFE Sanctuary, West Esplanade Manly 2095,
2 Department of Biological Sciences Macquarie University Sydney, New South Wales, 2109.
3 Sydney Institute of Marine Science, Mosman, NSW 2089 Australia
* Corresponding author: paolo.momigliano@students.mq.edu.au
Manuscript in press at Pacific Conservation Biology
Abstract
The grey nurse shark (Carcharius taurus) is listed as threatened throughout much of its
global distribution, and as critically endangered in eastern Australia. Captive breeding
programs have thus far been largely unsuccessful and little is known of their mating system
in this context. Here we carry out a paternity analysis to determine if the mating system in
captivity is characterized by multiple mating, and whether poor offspring survival is
associated with a particular male. Tissue samples from grey nurse sharks were collected from
three potential sires, the two dams and nine pups housed at Manly SEA LIFE Sanctuary in
eastern Australia. Each individual was genotyped at seven microsatellite markers and three
cases of multiple paternity were inferred. No paternal link to stillborn (5), or scoliotic (2)
pups was indicated. For the first time, we show the natural wild phenomenon of multiple
paternity occurring in a captive environment.
Keywords: captive breeding, elasmobranch, microsatellite, multiple paternity
Introduction
Grey nurse sharks (Carcharias taurus) make ideal aquarium specimens, being large and long-
lived, and adults cope well within the confines of an aquarium (Gordon 1993, Smith et al.
2004). Wild animals spend much of their time in “gutters” and near shore environments
(Otway et al. 2003), and these conditions are easily replicated in captivity. It is for these
reasons, coupled with their conservation status, that grey nurse sharks are widely held in
public aquaria around the world (Gordon 1993, Smith et al. 2004).
The eastern Australian population of grey nurse sharks was fished to near-extinction in the
1960s and 1970s and is now listed as Critically Endangered in New South Wales (NSW)
waters and protected under the Environmental Protection and Biodiversity Conservation
(EPBC) Act (1999). Since 2002, there has been a no take policy from both eastern and
western populations for aquarium display purposes (enforced by the Australian Department
of the Environment through the EPBC Act), which in combination with very poor captive
breeding success has resulted in an aging captive population. The average estimated age of
east coast animals in captivity is 26.4 years (n=9). Given that the maximum known age for
grey nurse sharks is 35 years (Goldman et al. 2006), and a lifting of the moratorium on
collection for aquaria is not likely in the near future, an increased effort to maximize breeding
success is needed if this species is to be held in aquaria into the future. Only a handful of
aquaria worldwide have had breeding events (J. Choromanski, pers. com.) and there is no
record of a captive born animal producing viable offspring. A first step in the process of
establishing captive bred populations is to gather information on current breeding behavior in
captivity; such as whether multiple mating occurs and whether poor offspring survival can be
linked to particular parents.
Grey nurse sharks have an unusual reproductive mode involving intra-uterine cannibalism
and oophagy (Grant et al. 1983). Females have two uteri in which multiple eggs are fertilized,
often by multiple males (Chapman et al. 2013). The largest embryo in each uterus consumes
all other embryos (Grant et al. 1983), and the mother continues to ovulate in order to nourish
the surviving embryo (Grant et al. 1983). Each mature female produces two pups every
second year, very rarely up to four pups, resulting in one of the slowest reproductive rates of
all shark species (Grant et al. 1983). This low fecundity coupled with relatively slow
maturation rates of 6-7 years for males and 9-10 years for females (Goldman et al. 2006) has
hampered the recovery of the eastern Australian population of grey nurse sharks (NSW
Fisheries 2002) and emphasizes the requirement for successful breeding in captivity for
display purposes. To facilitate this we aim to provide the first genetic characterization of the
mating system in a captive situation. Here we carry out paternity analysis to ascertain
whether multiple paternity occurs in captivity and assess whether any relationship exists
between the paternity of pups and still-borne young.
Materials and methods
Sample collection
All adults (3 males and 2 females) were collected between 1985 and 1996 from wild stocks
in Eastern Australia, and housed in the same aquarium at Manly SEA LIFE Sanctuary
(MSLS) . Tissue samples were obtained from the three living candidate sires, one living dam,
one deceased dam, one living male that had been born in captivity and eight deceased captive
born pups that were all held at MSLS between 2000 and 2013. The nine samples from captive
born animals were from six separate pregnancies to the two known dams. Samples from live
individuals were taken from the dorsal or pectoral fins using a sterile biopsy punch during
routine interactions at MSLS. All tissue samples were stored in 70% ethanol at -20 °C.
DNA extraction and PCR
DNA was extracted from each individual tissue sample using a Bioline DNA extraction kit
following manufacturer's instructions. DNA quality was checked via gel electrophoresis, and
DNA concentration was quantified using a Nanodrop 1000 spectrophotometer (Thermo
Fisher Scientific, Inc.). Seven microsatellite loci were amplified by PCR: Cta45-69, Cta56-72
(Feldheim et al. 2007), Iox12 (Schrey and Heist 2002), Ct243, Ct417, Ct432 and Ct655
(Chapman et al. 2013). The primers we used for PCR amplification were either M13 labelled
primers (Schuelke 2000) or the forward primer was directly labeled using the fluorescent dye
6-FAMTM (Macrogen Inc. ). PCR conditions varied in accordance with the primers used
(Table 1). For directly fluorescently labelled primers we used 50ng of template DNA, 200
µM dNTPs, 0.5 µM of each primer, , 2.5-3 mM MgCl2, 1 unit of Promega Go Taq DNA
Polymerase and PCR buffer (following manufacturer’s instructions) in a total volume of
20µl. For M13 primers we used 50ng of template DNA, 200 µM dNTPs, 0.1 µM forward
primer with attached M13 tail, 0.5 µM µl reverse primer, 0.5µM M13 primer labeled with 6-
FAMTM, 2.5-3 mM MgCl2, 1 unit Promega Go Taq DNA Polymerase and PCR buffer
(following manufacturer's instructions), in a total volume of 20µl.
Thermocycling conditions were as follows: initial denaturation for three minutes at 94˚C,
then 35 cycles of 30 sec denaturation at 94˚C, 30 sec annealing (at the specific primer
annealing temperature) and 30 sec at 72˚C followed by a final 10 min extension at 72˚C. PCR
products were sent to Australian Genome Research Facility (AGRF) for fragment analysis
using an ABI 3730XL analyzer. Allele sizes were determined using an internal size standard
LIZ (GeneScanTM 500 LIZ) and the Peak ScannerTM software (version 1.0, both from Applied
Biosystems).
Analysis
To evaluate the suitability of the loci selected to estimate paternity via genetic exclusion, we
calculated the non-exclusion probability for the second parent given the observed allele
frequencies and Probability of Identity (PID) using the software Cervus 3.0 (Kalinowski et al.
2007). PID is the probability of two unrelated individuals sharing the same genotype. For
each litter we confirmed motheroffspring relationships by visually inspecting genotypes to
ensure that for each locus a pup shared at least one identical allele with its mother. Paternity
was then assigned both by exclusion and using the likelihood approach adopted by the
software Cervus 3.0. Given the size of the data set, genetic exclusion could be determined by
visually identifying mismatches. CERVUS assigns paternity while taking into account user-
defined scoring errors and the proportion of candidate parents sampled (100%). The program
calculates a logarithm-of-the-odds (LOD) score for all candidate parents and carries out
simulation to estimate the critical difference in LOD score between the most likely and
second most likely candidate parent, at confidence level that can be set by the user (in this
study 99% and 99.9%).
Results
Genotypes for five of the seven selected loci were obtained for all individuals, while for the
remaining two loci there were some missing data (Table 1 and Table 2). The number of
alleles per locus ranged between 2 and 8, and PID ranged from 0.004 to 0.6 (Table 1). The
combined non-exclusion probability for the second parent was 8x10-3, suggesting that even
with the limited number of loci, we can be confident of genetic exclusion. Genotypes for each
individual are given in Table 2.
The paternity of all nine pups was determined. The exclusion method and the maximum
likelihood approach yielded identical results. The maximum likelihood approach determined
paternity of each pup with confidence levels higher than 99% (Table 3). We identified three
separate cases of multiple paternity, whereby siblings from the same pregnancies were sired
by different fathers (Maia-Apollo, GNS4-GNS5 and Atlas-Murdoch ) (Table 3).
Discussion.
This is the first time multiple paternity has been identified in captive grey nurse sharks.
Multiple paternity has been described in a number of elasmobranch species (Saville et al.
2002, Daly-Engel et al. 2007, Fitzpatrick et al. 2012) and increases genetic diversity among
offspring (Fitzpatrick et al. 2012). Multiple paternity in grey nurse sharks, while long
suspected (Grant et al. 1983), has only recently been demonstrated in wild populations
(Chapman et al. 2013) where 60% of gravid females were fertilized by at least two males.
Captive observations of matings at MSLS have shown that an individual female may mate
multiple times with the same or different males over the course of the mating season
(personal observations; Gordon 1993).
All available males sired at least one offspring that survived greater than one year, however,
each of the males also sired stillborn young. These results suggest that reduced survival times
of captive born grey nurse sharks may not be not due to genetic factors and that the captive
environment may be responsible. Nonetheless, it has also been demonstrated that grey nurse
sharks from eastern Australian have especially low genetic variation (Stow et al. 2006,
Ahonen et al. 2009), and low genetic variation might reflect inbreeding (Frankham et al.
2002). Inbreeding depression may lead to poor fertility and low survival rates, therefore a
worrying explanation might be that the poor survival being observed in captivity reflects
survival rates in the wild eastern Australian population.
Captive-born east Australian grey nurse sharks frequently succumb to scoliosis with two out
of the three pups at MSLS that survived longer than a year eventually dying from
complications associated with scoliosis. Recent work on scoliotic animals in captivity
suggests external influences such as manual handling of animals, swim patterns and vitamin
intake, rather than genetic factors, are responsible for scoliosis in captive grey nurse sharks.
Wild caught individuals brought into captivity at a smaller size while the cartilage skeleton
was still developing show a greater rate of scoliosis (Tate et al. 2013). The same factors may
be responsible for the scoliosis rate in captive born animals because young sharks are often
moved several times in the first few years of life, a process that often involves an element of
manual handling that may initiate scoliosis (Anderson et al. 2012). The factors responsible
for the high frequency of stillborn young observed in captivity are difficult to guess at.
Analysis of the genetic characteristics of the still born young provide no indication of any
association between genetic variation and still born young. For example, mean multilocus
heterozygosity of the still born young (0.73) was only marginally lower than the rest of the
sampled individuals (0.78). Nonetheless, measures of genetic variation at neutral markers can
be a poor proxy for genetic variation at functionally important parts of the genome (Hoffman
et al. 2008) and, as such, we cannot conclude that genetic factors are not responsible.
It is conceivable that the environmental needs for successful reproduction of grey nurse
sharks are not being replicated in captivity. Grey nurse sharks on the east coast of Australia
partake in long seasonal migrations and are subject to various changes in water temperature
as a result (Bansemer and Bennett, 2009). There is evidence that female grey nurse sharks
segregate from males while gravid and move towards the northern (warmer) end of their
range (Bansemer and Bennett, 2009). Aquaria holding grey nurse shark do not have the
capacity to mimic the temperature changes that would be experienced by female sharks
during these migrations nor do many have the ability to segregate gravid females from males.
These unnatural conditions may place undue stress on gravid animals that could result in the
high rate of still born pups in captivity. Other potential stressors for gravid sharks in captivity
could be stray voltage, unnatural photoperiods, noise and the close proximity of possible
predators (Smith et al. 2004).
The display of sharks by aquaria may play a role in conserving this taxonomic group through
public education. Awareness of the critically endangered status of grey nurse shark has been
heightened by their display in aquaria, but to perpetuate this message the survival of pups
born into captivity is critical. Determining the environmental and, potentially, genetic factors
associated with pup survival is fundamental to achieving this goal.
Acknowledgements.
The authors wish to acknowledge and thank Claudette Rechtorik and The SEA LIFE
Conservation fund for financing lab work for this project. Nick Otway (NSW Fisheries) for
advice and tissue samples. The Curatorial team at MSLS for tissue samples and histories.
References
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Table 1. Summary statistics for the loci used for paternity analysis. N= sample size,
K=number of alleles, PID=probability of identity. Forward primers were either fluorescently
labeled with 6 FAMtm (Labeled) or had a M13 tail at their 3' end (M13)
Locus
Repeat
N
K
Size
Range
Labeled/M13
Cta
45-69
(TG)20
14
5
149-173
M13
Cta
56-72
(AG)12
14
2
184-190
M13
Iox-12
(GT)8 GAGT(GA)4
14
4
325-331
Labeled
ct243
(TAGA)16
11
5
195-237
Labeled
ct415
(TAGA)27..(AGAC)8
9
8
341-381
Labeled
ct432
(TAGA)26
14
7
260-324
Labeled
ct655
(TATC)15
14
7
147-207
Labeled
Table 2. Microsatellite genotypes for each individual.
Individual
Sex/
pup
lox12
cta45-69
cta56-72
ct243
ct415
ct655
ct432
Artemis
F
327
331
163
171
184
184
0
0
0
0
167
179
264
302
Pallas
F
329
331
167
167
184
190
195
203
341
381
147
179
268
314
Patches
M
331
331
167
167
184
184
203
203
365
373
167
187
284
324
Trio
M
329
331
167
167
184
184
203
207
349
357
203
207
268
284
Huey
M
325
329
173
149
184
190
203
237
0
0
147
167
260
268
Maia
P
327
331
163
167
184
184
0
0
0
0
167
187
264
284
Apollo
P
329
331
163
167
184
184
203
203
357
369
167
207
284
302
Murdoch
P
325
329
149
167
184
190
195
237
0
0
147
167
268
268
Atlas
P
329
331
167
167
184
190
203
207
349
381
179
207
268
268
GNS4
P
331
331
163
167
184
184
203
233
369
373
179
187
264
284
GNS5
P
325
331
163
173
184
184
0
0
0
0
147
179
268
302
Phoebos
sib
P
327
331
167
171
184
184
203
203
353
373
167
167
284
302
GNS77
P
331
331
167
171
184
184
207
233
349
353
167
207
268
302
GNS86
P
327
331
167
171
184
184
207
233
349
369
167
207
264
268
Table 3: Survival and paternity of grey nurse shark pups at MSLS. Pups from the same litter
are identified by the same superscript (1, 2 or 3). The combined non-exclusion probability for
the second parent (exclusion method) was 8 x10-3.Confidence refers to confidence in
paternity assignment when the mother is known using the likelihood-simulation approach
implemented in Cervus 3.0.
Pup name
Sex
Date of Birth
Date of
Death
Survival
Mother
Candidate
Father
Confidence
Maia 1
Female
23/12/2001
25/01/2012
10 years*
Artemis
Patches
> 99.9%
Apollo 1
Male
23/12/2001
29/11/2004
3 years*
Artemis
Trio
> 99.9%
Atlas2
Male
29/06/2006, premature
06/07/2006
7 days
Pallas
Trio
> 99.9%
Murdoch2
Male
06/02/2007
Alive
7 years
Pallas
Huey
> 99.9%
gns86
Unkn.
04/10/2011
04/10/2011
Stillborn
Artemis
Trio
> 99%
gns77
Unkn.
19/09/2009
19/09/2009
Stillborn
Artemis
Trio
> 99%
gns43
Unkn.
22/02/2000
22/02/2000
Stillborn
Artemis
Patches
> 99.9%
gns53
Unkn.
22/02/2000
22/02/2000
Stillborn
Artemis
Huey
> 99.9%
Phebos sib
Unkn.
03/11/2003
03/11/2003
Stillborn
Artemis
Patches
> 99.9%
*Died from complications associated with scoliosis
... Corresponding to observation of reproductive behaviors, aquaria can take more deliberate steps to genetically test offspring. This information can play a role in linking reproductive behavior with genetic outcomes to further our understanding of female choice and multiple paternity (Heist and Feldheim, 2004), a widespread phenomenon across elasmobranch species both in situ (reviewed in Bester-van der Merwe et al., 2022) and ex situ (Janse et al., 2013;Townsend et al., 2015). Performing parentage analysis will provide institutions with an indication of which individuals are genetically overcontributing or undercontributing to the regional studbook and will enable facilities to coordinate breeding efforts effectively (Janse et al., 2013;Hook, 2019). ...
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As a basic conservation measure, the elasmobranch caretaker community needs to increase its level of peer review, constantly exchange information, and continually update prevailing husbandry practices. In addition, it should provide assistance to new and developing facilities, where less than ideal husbandry protocols may be adopted through lack of training or readily available information. Until the present day there has been no handbook enumerating the captive care of sharks and rays. Information has been available in scientific journals, the gray literature, and predominantly within the memories of experienced aquarium veterans, but it has been typically scattered and difficult to access. It seems incredible that the husbandry of such an important and charismatic group of animals has not been more comprehensively addressed in the literature. The Elasmobranch Husbandry Manual: Captive Care of Sharks, Rays and their Relatives attempts a first step toward addressing this oversight. The development of the Manual was slightly unorthodox and merits some description. It began as a bullet list of husbandry topics, tabled and discussed at the 1999 Regional Aquatic Workshop in Minneapolis, Minnesota (USA). This list was then fine-tuned over ensuing months by a steering committee established at the same meeting. The initial premise was to generate an exhaustive list of elasmobranch husbandry topics and then solicit contributions to match those topics from individuals considered to be leaders in their respective fields. As the Manual was conceived to be a conservation initiative, participation was to be, and indeed remained, entirely voluntary. As a catalyst to the development of the Manual the 1st International Elasmobranch Husbandry Symposium was held in Orlando, Florida (USA), between the 3rd and 7th of October in 2001. The first three days of the Symposium included invited papers, representing the formal chapters of the Manual, and an additional day was made available for the presentation of voluntary contributions and the discussion of a plan of action. Bringing together ~180 learned individuals from 16 countries, the Symposium provided an opportunity to exchange information about the husbandry of elasmobranchs and to conduct an informal peer review of the contributions made by invited speakers. Following the Symposium, invited contributions were then peer-reviewed in a more formal manner and the result is the Manual you are now reading. The ultimate objective of the Manual was to produce a single-reference handbook that could be used as a guide to the captive care of elasmobranchs, assisting in the development of new exhibits, aiding the training of husbandry personnel, and answering specific husbandry questions about this important taxonomic group. In addition, it was a project objective to make the Manual available free-of-charge, via the World Wide Web, allowing anyone who might work with elasmobranchs ready access to the information. The resulting website is to be used as a forum to distribute the Manual, to post Manual updates, and to provide additional information and husbandry tools useful to elasmobranch caretakers. A number of articles presented at the 1st International Elasmobranch Husbandry Symposium were deemed to be of lesser immediate relevance and were not included in the Manual. These articles, in combination with archive articles from previous issues of Drum and Croaker, have been compiled by Peter J. Mohan (editor of Drum and Croaker) and published as The Shark Supplement: 40 Years of Elasmobranch Husbandry Science, Speculation, and Apocrypha (Drum and Croaker Special Edition No. 2). This supplement may be accessed through either the Manual or the Drum and Croaker websites. Aquariology is an emerging science and many experienced aquarium professionals have little formal scientific training, yet many of these individuals have years of valuable hands-on experience. Conversely, many workers who actively cooperate with public aquariums are professional academics and respected leaders in their respective fields. The Manual brings together contributions from both ends of this spectrum. This process has given the Manual an inclusive and, at times, a slightly eclectic feel. Rather than detract from the merit of individual contributions, or indeed the broad coverage of the manual, we believe that this unique characteristic enhances the accessibility and ultimately the applicability of the Manual. It was always considered that the Manual would serve, in part, as a bridge between pure science and applied aquariology, and we trust that this goal has been achieved.
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For over a decade, we have been studying the reproductive behavior of the nurse shark, Ginglymostoma cirratum, in the Dry Torugas off the Florida Keys, an important mating and nursery ground for this species. In the course of these studies, we have used a variety of tags and tagging protocols to monitor individual animals. Here we report the use of molecular methods for the genetic analysis of nurse sharks. Specifically we have analyzed genetic variation at the MHC II alpha locus using the polymerase chain reaction (PCR) followed by restriction fragment length polymorphism (RFLP) analysis of the amplified products. We found this technique to be a relatively rapid and reliable method for identifying genetic differences between individual sharks. Applying this method to a family of sharks consisting of a mother and 32 pups, we demonstrate that at least four fathers must have fathered this brood. Multiple paternity in the nurse shark suggests a mechanism by which populations of this species may maximize genetic variability. This seems especially valuable for philopatric species whose migratory movement, and thus potential for genetic diversity, is limited.
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Sand tiger sharks (Carcharias taurus) have an unusual mode of reproduction, whereby the first embryos in each of the paired uteri to reach a certain size ('hatchlings') consume all of their smaller siblings during gestation ('embryonic cannibalism' or EC). If females commonly mate with multiple males ('behavioural polyandry') then litters could initially have multiple sires. It is possible, however, that EC could exclude of all but one of these sires from producing offspring thus influencing the species genetic mating system ('genetic monogamy'). Here, we use microsatellite DNA profiling of mothers and their litters (n = 15, from two to nine embryos per litter) to quantify the frequency of behavioural and genetic polyandry in this system. We conservatively estimate that nine of the females we examined (60%) were behaviourally polyandrous. The genetic mating system was characterized by assessing sibling relationships between hatchlings and revealed only 40 per cent genetic polyandry (i.e. hatchlings were full siblings in 60% of litters). The discrepancy stemmed from three females that were initially fertilized by multiple males but only produced hatchlings with one of them. This reveals that males can be excluded even after fertilizing ova and that some instances of genetic monogamy in this population arise from the reduction in litter size by EC. More research is needed on how cryptic post-copulatory and post-zygotic processes contribute to determining paternity and bridging the behavioural and genetic mating systems of viviparous species.
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A number of captive sandtiger sharks (Carcharias taurus) in public aquaria have developed spinal deformities over the past decade, ranging in severity from mild curvature to spinal fracture and severe subluxation. To determine the frequency and etiologic basis of this disease, U.S. public aquaria participated in a two-stage epidemiologic study of resident sharks: 1) a history and husbandry survey and 2) hematology, clinical chemistry, and radiography conducted during health exams. Eighteen aquaria submitted data, samples, or both from 73 specimens, including 19 affected sharks (26%). Sharks caught off the Rhode Island coast or by pound net were smaller at capture and demonstrated a higher prevalence of deformity than did larger sharks caught from other areas via hook and line. Relative to healthy sharks, affected sharks were deficient in zinc, potassium, and vitamins C and E. Capture and transport results lead to two likely etiologic hypotheses: 1) that the pound-net capture process induces spinal trauma that becomes exacerbated over time in aquarium environments or 2) that small (and presumably young) sharks caught by pound net are exposed to disease-promoting conditions (including diet or habitat deficiencies) in aquaria during the critical growth phase of their life history. The last hypothesis is further supported by nutrient deficiencies among affected sharks documented in this study; potassium, zinc, and vitamin C play critical roles in proper cartilage-collagen development and maintenance. These correlative findings indicate that public aquaria give careful consideration to choice of collection methods and size at capture and supplement diets to provide nutrients required for proper development and maintenance of cartilaginous tissue.
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Elasmobranch mating systems have received growing attention in the past few years due to worldwide overexploitation of shark populations. Few studies to date have examined mating systems in sharks because of difficulty in sampling. The sandbar shark (Carcharhinus plumbeus) is heavily harvested around the world and is the dominant species in the main commercial fishery for large coastal sharks in the United States. In contrast, Hawaii hosts one of the few unexploited populations of sandbar sharks, and represents an opportunity to gather data on the reproductive biology of a vulnerable shark species without the confounding effects of fishing mortality. We examined the frequency of multiple paternity in Hawaiian sandbar sharks using 130 individuals (20 gravid females with 3-8 pups each per litter) surveyed with 6 polymorphic microsatellite loci, and determined that 8 of the 20 litters (40%) were multiply sired. A Bayesian approach estimated the frequency of multiple mating in this population at 43.8%, with a 95% confidence interval of 23-63%. We conclude that multiple paternity and genetic monogamy occur with roughly equal frequency in the Hawaiian sandbar shark population. This study may serve as groundwork for understanding the impact of commercial fishing pressure on elasmobranch mating systems.
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Age and growth estimates for sand tiger sharks, Carcharias taurus, in the western North Atlantic were derived from 96 vertebral centra collected from sharks ranging from 94 to 277 cm total length (TL), and compared to previously published age and growth data. The oldest female and male sand tiger sharks aged in this study were 17 and 15 years of age, respectively. von Bertalanffy growth parameters derived from vertebral length-at-age data are L ∞ = 295.8 cm TL, k = 0.11 year−1, and t 0 = −4.2 years for females, and L ∞ = 249.5 cm TL, k = 0.16 year−1, and t 0 = −3.4 years for males. Sexual maturity is estimated to be 9–10 years for females and 6–7 years for males. Weight-to-length relationships determined for female and male sand tiger sharks in the western North Atlantic are; W = 1.3 × 10−4 × L 2.4 (r 2 = 0.84, n = 55) and W = 9.0 × 10−5 × L2.5 (r 2 = 0.84, n = 47), respectively, and 7.9 × 10−5 × L 2.5 (r 2 = 0.84) for the sexes combined. Our results show sand tigers possess a slower rate of growth than previously thought. This information is crucial for accurately assessing this population’s ability to recover, and further justifies the need for this species to be fully protected.
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We report on the isolation of eight microsatellites from the sand tiger shark, Carcharias taurus, using an enrichment protocol. All loci, with the exception of Cta45–183, were in Hardy–Weinberg equilibrium. Loci exhibited three to 15 alleles, and observed and expected heterozygosities of 0.095–1.000 and 0.284–0.924, respectively. An additional marker (Iox-12) developed from a shortfin mako library was variable in sand tigers. These markers will be used to examine population genetics and mating patterns of this imperilled species.
Article
Three bouts of pre-copulatory behaviour were observed in a captive colony of sandtiger sharks,Carcharias taurus, at Oceanworld Manly, Sydney, Australia. The behaviour occurred 14 rather than 12 months apart. Temperature was very similar to that of local coastal conditions where these animals naturally occur. But the photoperiod was artificial and inflexible. The information recorded in all of these cases was almost identical, giving an insight into a very complex social structure in this essentially colonial animal. Dominance displays occurred between both mature and immature males in addition to aggression towards other objects, e.g. small carcharbinid sharks. Most interesting were the interactions between the males and females, especially those which implicate the possible use of chemical stimulants (pheromones). Copulation was observed on two occasions but was not filmed.