Sandbar Shark Carcharhinus Plumbeus Research Articles

Effects of Altered Stock Assessment Frequency on the Management of a Large Coastal Shark

AbstractStock assessments are particularly resource‐intensive processes. Demand for assessments typically exceeds capacity, stimulating interest in reducing stock assessment frequency for suitable species. Species with slow population growth rates, low economic importance, and low recruitment variability, like coastal sharks in the USA, have been identified as appropriate candidates for long‐interim assessment periods. We conducted a Stock Synthesis–based management strategy evaluation with a threshold harvest rate control rule within the southeastern USA to assess the impact of stock assessment frequency for the slow‐growing Sandbar Shark Carcharhinus plumbeus. Stock assessments for the Sandbar Shark in the southeastern USA have been conducted or updated every 4–6 years since 1998. The Sandbar Shark proved to be a particularly good candidate species for reduced assessment frequency, as noted by unaffected management procedure performance across interim periods of 1, 5, and 10 years. Management objectives, including probability of stock recovery, relative biomass level, cumulative U.S. commercial catch, and probability of overfishing, were minimally adversely impacted with interim periods equal to 15 years. Based on our findings, assessment frequency for large coastal shark species could reasonably be reduced in the future to once every 10 or more years without compromising management success.

Observations of juvenile sandbar sharks Carcharhinus plumbeus () around the Bojana River delta (Southern Adriatic Sea).

The sandbar shark (Carcharhinus plumbeus) is considered rare in the Adriatic Sea and the majority of records originate from the northern Adriatic, where a nursery area for this species close to the Po delta system has been repeatedly proposed. This study provides 5 new records and analyses the previously published records of sandbar sharks recorded around the delta of the River Bojana (in Montenegro, in the south-eastern Adriatic). The River Bojana located on the border between Montenegro and Albania, is the second largest river flowing into the Adriatic Sea, where it forms a highly productive ecosystem already known as a local hotspot for smooth-hound sharks (Mustelus spp.). New records of sandbar sharks have emerged as a result of citizen science (a social media survey) and direct reports from fishermen. The total length of C. plumbeus juveniles ranged from approximately 800 mm to 1100 mm, and most (n=5) were caught by set gillnets. The data presented here show that juveniles are consistently present around the estuary and indicate the importance of this fragile estuarine ecosystem for sandbar sharks. Additionally, this study also provides morphometric data collected from a single individual.

Highly migratory species predictive spatial modeling (PRiSM): an analytical framework for assessing the performance of spatial fisheries management

Spatial management for highly migratory species (HMS) is difficult due to many species’ mobile habits and the dynamic nature of oceanic habitats. Current static spatial management areas for fisheries in the United States have been in place for extended periods of time with limited data collection inside the areas, making any analysis of their efficacy challenging. Spatial modeling approaches can be specifically designed to integrate species data from outside of closed areas to project species distributions inside and outside closed areas relative to the fishery. We developed HMS-PRedictive Spatial Modeling (PRiSM), which uses fishery-dependent observer data of species’ presence–absence, oceanographic covariates, and gear covariates in a generalized additive model (GAM) framework to produce fishery interaction spatial models. Species fishery interaction distributions were generated monthly within the domain of two HMS longline fisheries and used to produce a series of performance metrics for HMS closed areas. PRiSM was tested on bycatch species, including shortfin mako shark (Isurus oxyrinchus), billfish (Istiophoridae), and leatherback sea turtle (Dermochelys coriacea) in a pelagic longline fishery, and sandbar shark (Carcharhinus plumbeus), dusky shark (C. obscurus), and scalloped hammerhead shark (Sphyrna lewini) in a bottom longline fishery. Model validation procedures suggest PRiSM performed well for these species. The closed area performance metrics provided an objective and flexible framework to compare distributions between closed and open areas under recent environmental conditions. Fisheries managers can use the metrics generated by PRiSM to supplement other streams of information and guide spatial management decisions to support sustainable fisheries.

Shark tooth collagen stable isotopes (δ15 N and δ13 C) as ecological proxies.

The isotopic composition of tooth-bound collagen has long been used to reconstruct dietary patterns of animals in extant and palaeoecological systems. For sharks that replace teeth rapidly in a conveyor-like system, stable isotopes of tooth collagen (δ13 CTeeth & δ15 NTeeth ) are poorly understood and lacking in ecological context relative to other non-lethally sampled tissues. This tissue holds promise, because shark jaws may preserve isotopic chronologies from which to infer individual-level ecological patterns across a range of temporal resolutions. Carbon and nitrogen stable isotope values were measured and compared between extracted tooth collagen and four other non-lethally sampled tissues of varying isotopic turnover rates: blood plasma, red blood cells, fin and muscle, from eight species of sharks. Individual-level isotopic variability of shark tooth collagen was evaluated by profiling teeth of different ages across whole jaws for the shortfin mako shark Isurus oxyrinchus and sandbar shark Carcharhinus plumbeus. Measurements of δ13 CTeeth and δ15 NTeeth were positively correlated with isotopic values from the four other tissues. Collagen δ13 C was consistently 13 C-enriched relative to all other tissues. Patterns for δ15 N were slightly less uniform; tooth collagen was generally 15 N-enriched relative to muscle and red blood cells, but congruent with fin and blood plasma (values clustered around a 1:1 relationship). Significant within-individual variability was observed across whole shortfin mako shark (δ13 C range=1.4‰, δ15 N range=3.6‰) and sandbar shark (δ13 C range=1.2‰-2.4‰, δ15 N range= 1.7‰-2.4‰) jaws, which trended with tooth age. We conclude that amino acid composition and associated patterns of isotopic fractionation result in predictable isotopic offsets between tissues. Within-individual variability of tooth collagen stable isotope values suggests teeth of different ages may serve as ecological chronologies, that could be applied to studies on migration and individual-level diet variation across diverse time-scales. Greater understanding of tooth replacement rates, isotopic turnover and associated fractionation of tooth collagen will help refine potential ecological inferences, outlining clear goals for future scientific inquiry.

Size Changes within a Southeastern United States Coastal Shark Assemblage: 1975–2018

AbstractHarvest may have myriad effects on target species, including a change in population size structure. To assess whether size shifts have occurred among managed coastal species of shark (superorder Selachimorpha), we examined the population size structure of 12 species caught during a nearly five‐decade‐long fishery‐independent survey conducted in Onslow Bay, North Carolina, using standardized longline gear. We evaluated trends in mean fork length (FL), median FL, and index of maximum FL (L90%) for each species separately across time using linear regression models. We also examined trends in size‐classes (200‐mm bins) and catch per unit effort for each species over time. For 10 of the 12 species (excluding sample‐size‐constrained Tiger Shark Galeocerdo cuvier and Bull Shark Carcharhinus leucas), size structure metrics indicated decreasing sizes over time, although statistical confidence for these patterns varied across species and metrics. Strongest statistical support for declining sizes was observed for Blacknose Shark Carcharhinus acronotus (mean FL, median FL, L90%), Dusky Shark Carcharhinus obscurus (L90%), Smooth Dogfish Mustelus canis (L90%), and Atlantic Sharpnose Shark Rhizoprionodon terraenovae (L90%). Magnitude of decreases in L90% among these 10 species during the survey ranged from roughly 9% (Silky Shark Carcharhinus falciformis; 83‐mm decrease) to 35% (Sandbar Shark Carcharhinus plumbeus; 541‐mm decrease). Our findings indicate a potential for fishing pressure to exert directional selection on these coastal shark species, although further research is needed regarding the nature of size‐dependent catchability and species‐specific vital rates to adequately evaluate these dynamics. Furthermore, in addition to the removal of “great sharks,” decreasing sizes of small coastal sharks, such as Blacknose Shark, Smooth Dogfish, and Atlantic Sharpnose Shark (i.e., “mesopredators”), suggest that harvest may have pervasive effects on species throughout this assemblage.

Using historical and citizen science data to improve knowledge about the occurrence of the elusive sandbar shark Carcharhinus plumbeus (Chondrichthyes - Carcharhinidae) in the Adriatic Sea.

The Mediterranean Sea is an extinction hotspot for sharks, skates, and rays, with at least half of all species being threatened. The sandbar shark Carcharhinus plumbeus is among the most threatened species and is declared endangered (EN) in the Mediterranean according to the IUCN Red List of Threatened Species. The Adriatic Sea was previously proposed to be an important nursery area for this species based on sporadic sightings of neonates and juveniles. However, this species is generally considered to be rare in this region, and reports of its presence are scarce. Here, we present new records for the sandbar shark in the Adriatic Sea and review spatial and temporal data accumulated from literature, museum specimens, and citizen science initiatives in an attempt to assess the distribution and seasonality of this species. The majority of the records were from neonate and juvenile sandbar sharks, and three hotspots for their occurrence could be identified: (1) the Emilia-Romagna region, (2) the Veneto region, and (3) the Gulf of Trieste. Our data indicate a high concentration of sandbar sharks around the delta of the Po river, emphasising the need for scientific surveys in this confined area in order to confirm a possible nursery ground. Data collected by citizen science initiatives reveal that this species is still present in the Adriatic Sea and might be more abundant than previously thought, underlining the potential of citizen science as a valuable tool to monitor the distribution of rare and endangered species.

Sandbar shark aggregation in the central Mediterranean Sea and potential effects of tourism

Abstract An aggregation of sandbar sharks Carcharhinus plumbeus occurs every summer around the remote uninhabited islet of Lampione (Pelagie Islands Marine Protected Area, south‐western Mediterranean Sea), attracting an increasing number of tourists for a shark watching experience. Despite the ecological and socio‐economic importance of this rare occurrence in Mediterranean waters, there is a lack of scientific data and lack of information as to the potential impact of tourist activities on the presence and behaviour of this shark species. Using baited underwater videos, this study provides the first assessment of this shark aggregation, as well as a preliminary evaluation of the potential effects that boating and diving activities may have on sandbar sharks during two different periods within the tourism season (July and September 2019). Overall, 241 sandbar shark sightings (with up to five individuals together) were recorded in July, whereas there were only six sightings in September. The average MaxN was 1.18 hr−1 (±0.21 hr−1 SE) and 0.22 hr−1 (±0.10 hr−1 SE) individuals in July and September respectively. Higher frequentation levels of divers and boats significantly reduced the number of shark sightings at the aggregation site. This study emphasizes the need for further investigations on Mediterranean shark aggregations and the implementation of specific conservation measures, such as an increase of protection level in Lampione and better enforcement, aside from strategies that promote sustainable tourism, including restrictions on the number of boats and divers’ visits per day. In the meantime, a precautionary approach aimed at regulating the interactions between tourists and sharks should be implemented through the application of a self‐regulatory code of conduct for divers when sharks aggregate around the island.

Sensitivity of a shark nursery habitat to a changing climate

Nursery area habitats such as estuaries are vital for the success of many fish populations. Climate change is altering conditions in these areas, which can thus impact the availability of suitable nursery habitat. The sandbar shark Carcharhinus plumbeus uses Chesapeake Bay (USA) as a nursery habitat during the summer months from birth up to 10 yr of age. To assess the impacts of climate change on juvenile sandbar sharks, we developed a habitat model using longline data collected from a fishery-independent survey within Chesapeake Bay. With this model, we projected contemporary and future distributions of suitable habitat for juvenile sandbar sharks in Chesapeake Bay under varying environmental regimes. Predicted suitable juvenile sandbar shark habitat was negatively impacted by future increases in temperature, but positively influenced by future decreases in dissolved oxygen. The latter trend was likely related to the habitat partitioning that occurs between different life stages. Changes in salinity had relatively small impacts. By end-of-century the projected amount of suitable bottom habitat decreased; however, when incorporating the entire water column, projected suitable habitat increased. This suggests that juvenile sandbar sharks may need to make a behavioral shift to avoid non-preferred conditions, which could alter their foraging ecology or refuge strategies. As nursery habitats change with climate change, it is crucial to understand how a species may be impacted during this vital life stage when trying to predict overall species success in the future.

Seasonal Presence of Atlantic Sturgeon and Sharks at Cape Hatteras, a Large Continental Shelf Constriction to Coastal Migration

AbstractCape Hatteras is a major topographic feature on the continental shelf of the U.S. eastern seaboard that changes the dynamics of nearshore large ocean currents, including the Labrador Current and Gulf Stream. Cape Hatteras constricts shelf habitat and restricts the migratory corridors of highly migratory species through this area. Our objective was to describe the seasonal patterns of presence for three species—the Spiny Dogfish Squalus acanthias, Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus, and Sandbar Shark Carcharhinus plumbeus—and analyze environmental conditions associated with fish presence near this feature. These species are managed under the Magnuson–Stevens Act, and two of them are also listed as species of concern under the Endangered Species Act. Transmitter detections from tagged fish recorded by the Cape Hatteras acoustic array, which was deployed just south of the cape, indicated that these species are present year‐round. The greatest number of detections occurred from November through April. This simple baseline of seasonal presence can provide insights for regional offshore development activities, which have the potential to affect movement patterns of migratory species through the Cape Hatteras constriction. Our results show the value of strategically placed acoustic arrays for observing fish habitat use and provide presence/absence data to enhance our understanding of species ecology and distribution.

Are circle hooks effective management measures in the pelagic longline fishery for sharks in the Gulf of Gabès?

Abstract This study evaluated the circle hook use as a tool for shark management in the pelagic longline fishery in the Gulf of Gabès. The usual J‐hook No. 2 with 10° offset, which has been traditionally used by the fishery, was compared to the 18/0 non‐offset circle hook in an alternating fashion along the main line. In total, 22 experimental longline sets were deployed through the shark fishing seasons of 2016 and 2017 to examine the effects of hook types on the catch composition, the catch rates, the hooking location, and the status at haulback. The catch composition differed significantly among hook types. Moreover, an overall increase in catch rates for the main species, the sandbar shark Carcharhinus plumbeus, and the shortfin mako shark Isurus oxyrinchus, was observed when using circle hooks. There was no size‐selective effect of circle hooks for the common species. The circle hooks were not effective at reducing at‐haulback mortality of sandbar shark. Conversely, shortfin mako and smooth‐hound shark Mustelus mustelus showed significantly lower relative mortality at haulback with circle hooks than with J‐hooks. Furthermore, circle hooks were more frequently hooked externally than the J‐hooks for the three shark species. Results demonstrated that the use of 18/0 non‐offset circle hooks in the pelagic shark longline fishery can reduce mortality at haulback for some species without any benefit for the dominant species, the sandbar shark. Overall, it is difficult to promote the adoption of the use of circle hooks as a management measure in this specialized fishery. Management measures focusing on fishing effort controls, fishing closures in critical habitats, and size limits could have significant benefits for the conservation of shark species and may help to improve the sustainability of the shark fishery in the Gulf of Gabès.

Resource-use dynamics of co-occurring chondrichthyans from the First Coast, North Florida, USA.

Recent studies on shark assemblages on the northeast Florida and southeast Georgia coast (hereafter referred to collectively as the "First Coast") have demonstrated differences in species and age-class composition of catch from previously characterized estuaries and newly surveyed area beaches, demonstrating that these regions may provide a critical habitat to different segments (i.e., life stages) of local shark populations. In this study, carbon and nitrogen stable isotopes (δ13 C and δ15 N) from muscle tissue and blood plasma were used to examine trophic dynamics (and temporal variability thereof) of the three dominant co-occurring species found along First Coast beaches (the Atlantic Sharpnose shark Rhizoprionodon terraenovae, Blacknose shark Carcharhinus acronotus and Blacktip shark Carcharhinus limbatus) to determine if they exhibit overlap in resource use along with spatial and temporal habitat use. Although considered spatially segregated from the beach species, a dominant, age-class species found in First Coast estuaries (juvenile Sandbar sharks Carcharhinus plumbeus) was also included in this analysis for comparison. Temporal variability of resource-use characteristics was detected at the species level. Resource-use overlap among species varied by tissue type and was generally higher for blood plasma, suggesting greater resource sharing over more recent time periods. Over longer time periods Atlantic Sharpnose and Blacktip sharks exhibited resource-use expansion, whereas Blacknose sharks exhibited a narrowing in resource use, suggesting a more specialized foraging strategy compared to the other species. The resource-use breadth of Sandbar sharks also expanded between blood plasma and muscle tissue. Significant size relationships were detected in Blacktip and Sandbar sharks, indicating ontogenetic resource shifts for both species. A diversity of highly productive resource pools likely support shark populations along the First Coast such that resource-use differentiation is not required to facilitate species co-occurrence. This work may shed light on understanding patterns of species co-occurrence as well as aid in future conservation efforts.

First Insights Into the Fine-Scale Movements of the Sandbar Shark, Carcharhinus plumbeus

The expanding use of biologging tags in studies of shark movement provides an opportunity to compare fine-scale movement behaviours among species. In May 2017, we deployed high-resolution biologging tags on four mature female sandbar sharks Carcharhinus plumbeus at Ningaloo Reef for durations ranging between 13 and 25.5 hours. Pressure and tri-axial motion sensors within these tags enabled the calculation of dive geometry, swimming kinematics and path tortuosity at fine spatial scales (m-km) and concurrent validation of these behaviours from video recordings. Sandbar sharks oscillated through the water column at shallow dive angles, with gliding behaviour observed in the descent phase for all sharks. Continual V-shaped oscillatory movements were occasionally interspersed by U-shaped dives that predominately occurred around dusk. The bottom phase of these U-shaped dives likely occurred on the seabed, with dead-reckoning revealing a highly tortuous, circling track. By combining these fine-scale behavioural observations with existing ecological knowledge of sandbar habitat and diet, we argue that this circling behaviour is likely to be a strategy for hunting benthic prey. Comparing dive geometry and energetics with those of other sharks reveals common patterns in energetically efficient oscillatory swimming.

Teeth penetration force of the tiger shark Galeocerdo cuvier and sandbar shark Carcharhinus plumbeus.

This study examined the minimum force required of functional teeth and replacement teeth in the tiger shark Galeocerdo cuvier and the sandbar shark Carcharhinus plumbeus to penetrate the scales and muscle of sheepshead Archosargus probatocephalus and pigfish Orthopristis chrysoptera. Penetration force ranged from 7·7-41·9 and 3·2-26·3 N to penetrate A. probatocephalus and O. chrysoptera, respectively. Replacement teeth required significantly less force to penetrate O. chrysoptera for both shark species, most probably due to microscopic wear of the tooth surfaces supporting the theory shark teeth are replaced regularly to ensure sharp teeth that are efficient for prey capture.

Confirmation of the occurrence of the sandbar shark Carcharhinus plumbeus (Nardo, 1827) at Norfolk Island, Tasman Sea.

The occurrence of the sandbar shark Carcharhinus plumbeus at Norfolk Island is confirmed. Carcharhinus plumbeus occurs over the mid to outer insular shelf from 38 m to at least 53 m depth, and appears to be at least as abundant as C. galapagensis in this habitat. No C. plumbeus were caught from shore despite most fishing effort being land-based. The presence of young-of-the-year confirms C. plumbeus breeds on the Norfolk Island shelf. Size at birth and the timing of parturition appear similar to that reported for eastern Australia.

The effects of pop-up satellite archival tags (PSATs) on the metabolic rate and swimming kinematics of juvenile sandbar shark Carcharhinus plumbeus

Pop-up satellite archival tags (PSATs) have been used since the 1990s to document the movements and post-release survival of numerous fish species. The effects of PSAT attachment on metabolic rate, cost of transport, and swimming kinematics have, however, not been broadly investigated. We therefore quantified the acute effects of PSAT attachment on these parameters in juvenile (47–87cm fork length) sandbar shark Carcharhinus plumbeus. Using a water tunnel, we also measured the lift and drag forces of PSATs from three manufacturers which allowed us to calculate the theoretical power costs of towing these devices. We found no evidence that PSAT attachment results in increases in metabolic rate or cost of transport, or influences swimming kinematics of juvenile sandbar shark at volitional swimming speeds. Applying drag force measurements obtained for PSATs to our data showed that the predicted fractional increase in metabolic rate engendered by towing one of these devices at a specified velocity, normalized by the metabolic rate when swimming at that velocity minus the standard metabolic rate, would be below 5%. Our results are therefore congruent and suggest that PSAT attachment does not negatively impact juvenile sandbar shark (and by extension other elasmobranch species of equivalent or larger body sizes and employing a similar swimming mode).

Aversive responses of captive sandbar sharks Carcharhinus plumbeus to strong magnetic fields.

This experimental study focused on the possible deterrent effect of permanent magnets on adult sandbar sharks Carcharhinus plumbeus. Results showed that the presence of a magnetic field significantly reduced the number of approaches of conditioned C. plumbeus towards a target indicating that adult C. plumbeus can be deterred by strong magnetic fields. These data, therefore, confirm that the use of magnetic devices to reduce shark by-catch is a promising avenue.

Isolation and characterization of eight microsatellite loci from Galeocerdo cuvier (tiger shark) and cross-amplification in Carcharhinus leucas, Carcharhinus brevipinna, Carcharhinus plumbeus and Sphyrna lewini.

The tiger shark Galeocerdo cuvier (Carcharhinidae) is a large elasmobranch suspected to have, as other apex predators, a keystone function in marine ecosystems and is currently considered Near Threatened (Red list IUCN). Knowledge on its ecology, which is crucial to design proper conservation and management plans, is very scarce. Here we describe the isolation of eight polymorphic microsatellite loci using 454 GS-FLX Titanium pyrosequencing of enriched DNA libraries. Their characteristics were tested on a population of tiger shark (n = 101) from Reunion Island (South-Western Indian Ocean). All loci were polymorphic with a number of alleles ranging from two to eight. No null alleles were detected and no linkage disequilibrium was detected after Bonferroni correction. Observed and expected heterozygosities ranged from 0.03 to 0.76 and from 0.03 to 0.77, respectively. No locus deviated from Hardy-Weinberg equilibrium and the global FIS of the population was of 0.04NS. Some of the eight loci developed here successfully cross-amplified in the bull shark Carcharhinus leucas (one locus), the spinner shark Carcharhinus brevipinna (four loci), the sandbar shark Carcharhinus plumbeus (five loci) and the scalloped hammerhead shark Sphyrna lewini (two loci). We also designed primers to amplify and sequence a mitochondrial marker, the control region. We sequenced 862 bp and found a low genetic diversity, with four polymorphic sites, a haplotype diversity of 0.15 and a nucleotide diversity of 2 × 10−4.

Histological and morphological aspects of reproduction in the sandbar shark Carcharhinus plumbeus in the U.S. south-eastern Atlantic Ocean and Gulf of Mexico.

The reproduction of the sandbar shark Carcharhinus plumbeus in the U.S. south-eastern Atlantic Ocean including the Gulf of Mexico was examined using a combination of histological and morphological characteristics of C. plumbeus collected through fishery-dependent and -independent sampling programmes (n = 1,567). Indices of maturity were constructed using measurements of gonads, reproductive tracts and claspers, and sandbar sharks exhibited 50% maturity sizes of 140 and 148 cm fork length for males and females respectively. Gonado-somatic indices and variation in reproductive tract condition were used to determine seasonal trends in reproduction of mature C. plumbeus. Sandbar sharks have discrete seasonal reproductive cycles in which males produce sperm from January to May with a peak in May and females develop eggs from January to May with ovulation occurring in June. Females were shown to exhibit a >2 year reproductive cycle. Embryonic development was assessed through measurements of masses and lengths of uterine contents. Gestation was 12 months, from July to the following June, with parturition in late June. This research highlights a difference from previously reported data on the periodicity of female reproduction in C. plumbeus in the U.S. south-eastern Atlantic Ocean and Gulf of Mexico, which may have major effects on future C. plumbeus stock management.

Trophic Ecology of a Predatory Community in a Shallow‐Water, High‐Salinity Estuary Assessed by Stable Isotope Analysis

AbstractEstuaries serve as habitats and nurseries for many recreationally and commercially important fishes, often contributing recruits to adult populations that remain in close proximity to estuarine environments. Upper‐level predatory fish species are among the most sought after by fisheries; thus, an understanding of the trophic dynamics of the community can assist ecological fisheries management of these highly productive ecosystems. Dietary niche overlap within the predatory fish community of Bulls Bay, a subtropical estuary in South Carolina, was assessed by using stable isotope analyses (δ13C and δ15N) to compare seven elasmobranch species and three teleost species. Cownose Rays Rhinoptera bonasus and Finetooth Sharks Carcharhinus isodon had no isotopic overlap with other species and therefore exhibited unique isotopic niche spaces that were indicative of potential resource partitioning. The teleosts and remaining elasmobranchs had varying degrees of overlap, implying shared resources; a high degree of dietary niche overlap was observed among Spotted Seatrout Cynoscion nebulosus, Sandbar Sharks Carcharhinus plumbeus, and Atlantic Sharpnose Sharks Rhizoprionodon terraenovae. Although most pairs of species showed some isotopic overlap, there were also interspecific differences in niche overlap, signifying that this predatory fish community has a widely varied prey base overall. Bulls Bay is an important nursery habitat with a balanced predator community, as illustrated by a combination of unique dietary niches and varying degrees of dietary niche overlap.Received August 31, 2015; accepted November 9, 2015

Characterisation and cross-amplification of 21 novel microsatellite loci for the dusky shark, Carcharhinus obscurus

The dusky shark Carcharhinus obscurus risks excessive fisheries exploitation worldwide due to its low productivity. Genetic monitoring is an effective way of resolving species stock structure, genetic diversity, and forensically identifying processed animals. Here we present the first C. obscurus species-specific microsatellite loci. Twenty-one di- to tetra-nucleotide loci with between 2 and 20 alleles per locus were developed. Observed heterozygosity ranged from 0.28 to 0.91 with only one locus slightly deviating from Hardy–Weinberg equilibrium. No significant evidence for null alleles or linkage disequilibrium was detected. These loci were cross-amplified in three related species. Seventeen, twelve, and eighteen loci exhibited polymorphism in sandbar shark Carcharhinus plumbeus, spinner shark Carcharhinus brevipinna, galapagos shark Carcharhinus galapagensis, respectively. Investigations into C. obscurus will benefit from these loci which possess attributes suitable for population-scale and individual-scale analyses. Additionally locus cross-amplification will facilitate research for these species with few existing microsatellites and similarly vulnerable life-histories.