The Behavioural and Genetic Mating System of the Sand Tiger Shark, Carcharias taurus, an Intrauterine Cannibal

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

Global Spatial Risk Assessment of Sharks Under the Footprint of Fisheries

Effective ocean management and conservation of highly migratory species depends on resolving overlap between animal movements and distributions and fishing effort. Yet, this information is lacking at a global scale. Here we show, using a big-data approach combining satellite-tracked movements of pelagic sharks and global fishing fleets, that 24% of the mean monthly space used by sharks falls under the footprint of pelagic longline fisheries. Space use hotspots of commercially valuable sharks and of internationally protected species had the highest overlap with longlines (up to 76% and 64%, respectively) and were also associated with significant increases in fishing effort. We conclude that pelagic sharks have limited spatial refuge from current levels of high-seas fishing effort. Results demonstrate an urgent need for conservation and management measures at high-seas shark hotspots and highlight the potential of simultaneous satellite surveillance of megafauna and fishers as a tool for near-real time, dynamic management

Reef sharks exhibit site-fidelity and higher relative abundance in marine reserves on the Mesoamerican Barrier Reef.

Carcharhinid sharks can make up a large fraction of the top predators inhabiting tropical marine ecosystems and have declined in many regions due to intense fishing pressure. There is some support for the hypothesis that carcharhinid species that complete their life-cycle within coral reef ecosystems, hereafter referred to as "reef sharks", are more abundant inside no-take marine reserves due to a reduction in fishing pressure (i.e., they benefit from marine reserves). Key predictions of this hypothesis are that (a) individual reef sharks exhibit high site-fidelity to these protected areas and (b) their relative abundance will generally be higher in these areas compared to fished reefs. To test this hypothesis for the first time in Caribbean coral reef ecosystems we combined acoustic monitoring and baited remote underwater video (BRUV) surveys to measure reef shark site-fidelity and relative abundance, respectively. We focused on the Caribbean reef shark (Carcharhinus perezi), the most common reef shark in the Western Atlantic, at Glover's Reef Marine Reserve (GRMR), Belize. Acoustically tagged sharks (N = 34) were detected throughout the year at this location and exhibited strong site-fidelity. Shark presence or absence on 200 BRUVs deployed at GRMR and three other sites (another reserve site and two fished reefs) showed that the factor "marine reserve" had a significant positive effect on reef shark presence. We rejected environmental factors or site-environment interactions as predominant drivers of this pattern. These results are consistent with the hypothesis that marine reserves can benefit reef shark populations and we suggest new hypotheses to determine the underlying mechanism(s) involved: reduced fishing mortality or enhanced prey availability

Compound character attributes (<i>c</i>CA) for CITES-listed shark species.

<p>Position numbers (bold) are from the beginning of the COI gene.</p><p>Compound character attributes (<i>c</i>CA) for CITES-listed shark species.</p

Sequence matching results in NCBI BLAST and BOLD of unknown processed fins and fin soup samples.

<p># = fin sample identifier, Type = processed fin (P) or soup (S), Loc = Collection location (HK = Hong Kong, USA = United States of America), BOLD = 100% identification at the lowest taxon possible (genus or species) in a Fish Barcode of Life Initiative (FISH-BOL) search, BLAST top hit = closest match in GenBank BLAST search (Coverage, Identity and UNQ (wheter or not the match was unique to that species refer to this search), I.D. = best identification based on the two searches.</p><p>Sequence matching results in NCBI BLAST and BOLD of unknown processed fins and fin soup samples.</p

Samples of known species identity tested for amplification (AMP) and sequencing (SEQ) performance with the mini-barcode assay.

<p>* denotes a species identified by Clarke et al. (2006) as making up a large fraction of the fin trade. N = Number of individuals tested. “Tests” denotes whether the samples were used to test for positive amplification (“AMP”) and/or sequencing this amplicon (“SEQ”).</p><p>Samples of known species identity tested for amplification (AMP) and sequencing (SEQ) performance with the mini-barcode assay.</p

Complex movements, philopatry and expanded depth range of a severely threatened pelagic shark, the oceanic whitetip (Carcharhinus longimanus) in the western North Atlantic.

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 500 km of the tagging site for ~30 days before dispersing across 16,422 km(2) of the western North Atlantic. Maximum individual displacement from the tagging site ranged from 290-1940 km 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 of sharks is illegal, were generally high (mean = 68.2% of time). Sharks spent 99.7% of their time shallower than 200 m 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 1082 m 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 0-125 m depths, which they may encounter from June to October after leaving the protected waters of The Bahamas EEZ

Species composition of the international shark fin trade assessed through a retail‐market survey in Hong Kong

The shark fin trade is a major driver of shark exploitation in fisheries all over the world, most of which are not managed on a species‐specific basis. Species‐specific trade information highlights taxa of particular concern and can be used to assess the efficacy of management measures and anticipate emerging threats. The species composition of the Hong Kong Special Administrative Region of China, one of the world's largest fin trading hubs, was partially assessed in 1999–2001. We randomly selected and genetically identified fin trimmings (n = 4800), produced during fin processing, from the retail market of Hong Kong in 2014–2015 to assess contemporary species composition of the fin trade. We used nonparametric species estimators to determine that at least 76 species of sharks, batoids, and chimaeras supplied the fin trade and a Bayesian model to determine their relative proportion in the market. The diversity of traded species suggests species substitution could mask depletion of vulnerable species; one‐third of identified species are threatened with extinction. The Bayesian model suggested that 8 species each comprised >1% of the fin trimmings (34.1–64.2% for blue [Prionace glauca], 0.2–1.2% for bull [Carcharhinus leucas] and shortfin mako [Isurus oxyrinchus]); thus, trade was skewed to a few globally distributed species. Several other coastal sharks, batoids, and chimaeras are in the trade but poorly managed. Fewer than 10 of the species we modeled have sustainably managed fisheries anywhere in their range, and the most common species in trade, the blue shark, was not among them. Our study and approach serve as a baseline to track changes in composition of species in the fin trade over time to better understand patterns of exploitation and assess the effects of emerging management actions for these animals.Composición de Especies del Mercado Internacional de Aleta de Tiburón Evaluada por medio de un Censo de Mercado al Menudeo en Hong KongResumenEl mercado de aleta de tiburón es un importante conductor de la explotación de tiburones a nivel mundial, la mayoría de los cuales no están manejados a un nivel específico de especie. La información específica de especies en el mercado resalta taxones de preocupación particular y puede usarse para avaluar la eficiencia de las medidas de manejo y anticipar las amenazas emergentes. La composición de especies en la Región Administrativa Especial de Hong Kong de la República Popular China, uno de los puntos más grandes de venta de aletas, fue evaluada parcialmente entre 1999 y 2001. Seleccionamos al azar e identificamos genéticamente pedazos de aletas (n = 4800) producidos durante el procesamiento de las aletas, en el mercado al menudeo de Hong Kong entre 2014 y 2015 para evaluar la composición contemporánea de especies dentro del mercado de aletas. Utilizamos estimadores no‐paramétricos de especies para determinar que al menos 76 especies de tiburones, batoideos y quimeras suministraban al mercado de aletas y un modelo bayesiano para determinar su proporción relativa dentro del mercado. La diversidad de las especies en el mercado sugiere que la sustitución de especies podría enmascarar la disminución de las especies vulnerables; un tercio de las especies identificadas enfrentan riesgos severos de extinción. El modelo bayesiano sugirió que cada una de ocho especies constituyó >1% de los pedazos de aletas (34.1‐64.2% para el tiburón azul [Prionace glauca]; 0.2‐1.2% para el tiburón toro [Carcharhinus leucas] y el tiburón mako [Isurus oxyrinchus]); así, el mercado estuvo sesgado a unas cuantas especies con distribución mundial. Muchos otros tiburones costeros, batoideos y quimeras están en el mercado pero con un manejo muy pobre. Menos de diez de las especies que modelamos tienen pesquerías manejadas sustentablemente en cualquier parte de su extensión, incluyendo a la especie más común en el mercado, el tiburón azul. Nuestro estudio y nuestra estrategia sirven como una línea de base para rastrear los cambios en la composición de las especies dentro del mercado de aletas a través del tiempo para entender mejor los patrones de explotación y evaluar los efectos de las acciones de manejo emergentes para estos animales.Article impact statement: One‐third of species traded in the Hong Kong shark fin market are threatened with extinction and <10 modeled have sustainably managed fisheries

The AIC and BIC values for models with random effects (in bold).

<p>The AIC and BIC values for models with random effects (in bold).</p