Authors in bold are/were staff or students of the Institute for Ocean Conservation Science and its founding organization, the Pew Institute for Ocean Science.
Feldheim, K.A., Gruber, S.H., DiBattista, J.D., Babcock, E.A., Kessel, S.A., Hendry, A.P., Pikitch, E.K., Ashley, M.V., Chapman, D.D. 2014. Two decades of genetic profiling yields first evidence of natal philopatry and long-term fidelity to parturition sites in sharks. Molecular Ecology, 23(1).
Sharks are a globally threatened group of marine fishes that often breed in their natal region of origin. There has even been speculation that female sharks return to their exact birthplace to breed (“natal philopatry”), which would have important conservation implications. Genetic profiling of lemon sharks (Negaprion brevirostris) from 20consecutive cohorts (1993-2012) at Bimini, Bahamas showed that certain females faithfully gave birth at this site for nearly two decades. At least six females born in the1993-1997 cohorts returned to give birth 14-17 years later, providing the first direct evidence of natal philopatry in the chondrichthyans. Long-term fidelity to specific nursery sites coupled with natal philopatry highlights the merits of emerging spatial and local conservation efforts for these threatened predators.
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O’Leary, S.J., Hice, L.A., Feldheim, K.A., Frisk, M.G., McElroy, A.E., Fast, M.D., Chapman, D.D. 2013. Severe Inbreeding and Small Effective Number of Breeders in a Formerly Abundant Marine Fish. PLOS ONE 8(6).
In contrast to freshwater fish it is presumed that marine fish are unlikely to spawn with close relatives due to the dilution effect of large breeding populations and their propensity for movement and reproductive mixing. Inbreeding is therefore not typically a focal concern of marine fish management. We measured the effective number of breeders in 6 New York estuaries for winter flounder (Pseudopleuronectes americanus), a formerly abundant fish, using 11 microsatellite markers (6–56 alleles per locus). The effective number of breeders for 1–2 years was remarkably small, with point estimates ranging from 65–289 individuals. Excess homozygosity was detected at 10 loci in all bays (FIS = 0.169–0.283) and individuals exhibited high average internal relatedness (IR; mean = 0.226). These both indicate that inbreeding is very common in all bays, after testing for and ruling out alternative explanations such as technical and sampling artifacts. This study demonstrates that even historically common marine fish can be prone to inbreeding, a factor that should be considered in fisheries management and conservation plans.
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Chapman D.D., Wintner S.P., Abercrombie D.L., Ashe J., Bernard, A.M., Shivji, M.S., Feldheim, K.A. 2013. The behavioural and genetic mating system of the sand tiger shark, Carcharias taurus, an intrauterine cannibal. Biology Letters 9 (3).
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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The Washington Post
Worm B., Davis, B., Kettemer L., Ward-Paige, C.A., Chapman, D.D., Heithaus, M.R., Kessel, S., Gruber, S.H. 2013. Global catches, exploitation rates and rebuilding options for sharks. Marine Policy, 40 (194-204).
Adequate conservation and management of shark populations is becoming increasingly important on a global scale, especially because many species are exceptionally vulnerable to overfishing. Yet, reported catch statistics for sharks are incomplete, and mortality estimates have not been available for sharks as a group. Here, the global catch and mortality of sharks from reported and unreported landings, discards, and shark finning are being estimated at 1.44 million metric tons for the year 2000, and at only slightly less in 2010 (1.41million tons). Based on an analysis of average shark weights, this translates into total annual mortality of about 100 million sharks in 2000, and about 97 million sharks in 2010, with a total range of possible values between 63 and 273 million sharks per year. Further, the exploitation rate for sharks as a group was calculated by dividing total two independent mortality estimates by an estimate of total global biomass. As an alternative approach, exploitation rates for individual shark populations were compiled and averaged from stock assessments and other published sources. The resulting three independent estimates of the average exploitation rate ranged between 6.4% and 7.9% of sharks killed per year. This exceeds the average rebound rate for many shark populations, estimated from the life history information on 62 shark species (rebound rates averaged 4.9% per year), and explains the ongoing declines in most populations for which data exist. The consequences of these unsustainable catch and mortality rates for marine ecosystems could be substantial. Global total shark mortality, therefore, needs to be reduced drastically in order to rebuild depleted populations and restore marine ecosystems with functional top predators.
Howey-Jordan L.A., Brooks E.J., Abercrombie D.L., Jordan L.K.B., Brooks A., Williams, S., Gospodarczyk, E., Chapman, D.D. 2013. Complex Movements, Philopatry and Expanded Depth Range of a Severely Threatened Pelagic Shark, the Oceanic Whitetip (Carcharhinus longimanus) in the Western North Atlantic. PLOS ONE 8(2).
Oceanic whitetip sharks (Carcharhinus longimanus) have recently been targeted for conservation in the western North Atlantic following severe declines in abundance. Pop-up satellite archival tags were applied to 11 mature oceanic whitetips (10 females, 1 male) near Cat Island in the central Bahamas 1-8 May 2011 to provide information about the horizontal and vertical movements of this species. Another large female was opportunistically tagged in the U.S. Exclusive Economic Zone (EEZ). Data from 1,563 total tracking days and 1,142,598 combined depth and temperature readings were obtained. Sharks tagged at Cat Island stayed within 500km of the tagging site for ~30 days before dispersing across 16,422km2 of the western North Atlantic. Maximum individual displacement from the tagging site ranged from 290 to 1940km after times at liberty from 30–245 days, with individuals moving to several different destinations (the northern Lesser Antilles, the northern Bahamas, and north of the Windward Passage). Many sharks returned to The Bahamas after ~ 150 days. Estimated residency times within The Bahamas EEZ, where longlining and commercial trade in sharks is illegal, were generally high (mean = 68.2% of time). Sharks spent 99.7% of their time shallower than 200m and did not exhibit differences in day and night mean depths. There was a positive correlation between daily sea surface temperature and mean depth occupied, suggesting possible behavioral thermoregulation. All individuals made short duration (mean 13.06 minutes) dives into the mesopelagic zone (down to 1082m and 7.75°C), which occurred significantly more often at night. Ascent rates during these dives were significantly slower than descent rates, suggesting that these dives are for foraging. The sharks tracked appear to be most vulnerable to pelagic fishing gear deployed from 0–125m depths, which they may encounter from June to October after leaving the protected waters of the Bahamas EEZ.
Chapman, D.D., Frisk, M.G., Abercrombie, D.L., Safina, C., Gruber, S.H., Babcock, E.A., Feldheim, K.A., Pikitch, E.K., Davis, B., Kessel, S., Heithaus, M., Worm, B. 2013. Letter to the editor: Give shark sanctuaries a chance. Science, 339(6121): 757.
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