Carcharhinus Obscurus Research Articles

Historical introgression drives pervasive mitochondrial admixture between two species of pelagic sharks

We use a genomic sampling of both nuclear and mitochondrial DNA markers to examine a pattern of genetic admixture between Carcharhinus galapagensis (Galapagos sharks) and Carcharhinus obscurus (dusky sharks), two well-known and closely related sharks that have been recognized as valid species for more than 100years. We describe widespread mitochondrial-nuclear discordance in which these species are readily distinguishable based on 2152 nuclear single nucleotide polymorphisms from 910 independent autosomal regions, but show pervasive mitochondrial admixture. The species are superficially morphologically cryptic as adults but show marked differences in internal anatomy, as well as niche separation. There was no indication of ongoing hybridization between the species. We conclude that the observed mitochondrial-nuclear discordance is likely due to historical mitochondrial introgression following a range expansion.

Temporal patterns in the size of the main commercial shark species of Western Australia

Declines in the mean size of harvested organisms may indicate overexploitation. In the present study, temporal patterns in the mean size of the four main commercial shark species of Western Australia were evaluated. Unlike commonly observed for other shark populations, there were no strong temporal patterns in the mean size of gummy, dusky and whiskery sharks, whereas the mean size of sandbar sharks showed a gradual increase since 1993. These observations add further evidence that sharks can be fished sustainably when adequate monitoring, assessment and management actions are implemented.

Assessing multiple paternity in three commercially exploited shark species: Mustelus mustelus, Carcharhinus obscurus and Sphyrna lewini.

In this study, multiple paternity (MP) was investigated in three commercially important shark species, common smoothhound Mustelus mustelus, dusky shark Carcharhinus obscurus and scalloped hammerhead Sphyrna lewini occurring in southern Africa. Reduced marker panels of between five and six microsatellite loci were constructed for each species and used to genotype and assess the presence of MP in a total of 60 M. mustelus individuals from six litters, 90 C. obscurus individuals from 14 litters and 54 S. lewini individuals from 13 litters. Analysis in GERUD and COLONY revealed the presence of MP in all three species. Multiple paternities were observed in 67, 35 and 46% of the litters of M. mustelus, C. obscurus and S. lewini, with corresponding average sire size of 1·6, 1·4 and 2·0, respectively. The variation in the rate of MP among the three species is in accordance with previous studies whilst the comparatively high frequency of MP observed for M. mustelus, matches what has previously been reported for shark species demonstrating aggregation behaviour.

Slow life-history traits of a neritic predator, the bronze whaler (Carcharhinus brachyurus)

Intra-species plasticity in the life-history characteristics of sharks leads to the need for regional estimates to accurately determine resilience to anthropogenic effects. The present study provides the first length-at-age, growth and maturity estimates for the bronze whaler (Carcharhinus brachyurus) from southern Australia. Age estimates were obtained from vertebral sections of 466 individuals spanning 50–308-cm total length. Maximum estimates of age for males and females were 25 and 31 years respectively. The three-parameter logistic model for females (L∞=308cm LT, k=0.15, α=742) and for males (L∞=317cm LT, k=0.13, α=782) provided the best fit to the size at age data. Males matured at a similar age (16 years), but smaller size than females (224v. 270cm LT). Growth parameters and age-at-maturity estimates were similar to those for genetically isolated C. brachyurus populations, and the sympatric dusky shark (C. obscurus). The southern Australian C. brachyurus population is long-lived, slow growing and late maturing. These growth parameters are needed to undertake demographic analyses to assess the resilience of C. brachyurus to fishing, and provide an example of a wide-ranging elasmobranch with similar life-history characteristics across isolated populations.

Patterns of Occurrence of Sharks in Sydney Harbour, a Large Urbanised Estuary.

Information about spatial and temporal variability in the distribution and abundance of shark-populations are required for their conservation, management and to update measures designed to mitigate human-shark interactions. However, because some species of sharks are mobile, migratory and occur in relatively small numbers, estimating their patterns of distribution and abundance can be very difficult. In this study, we used a hierarchical sampling design to examine differences in the composition of species, size- and sex-structures of sharks sampled with bottom-set longlines in three different areas with increasing distance from the entrance of Sydney Harbour, a large urbanised estuary. During two years of sampling, we obtained data for four species of sharks (Port Jackson, Heterodontus portusjacksoni; wobbegong, Orectolobus maculatus; dusky whaler, Carcharhinus obscurus and bull shark, Carcharhinus leucas). Only a few O. maculatus and C. obscurus were caught, all in the area closest to the entrance of the Harbour. O. maculatus were caught in all seasons, except summer, while C. obscurus was only caught in summer. Heterodontus portusjacksoni were the most abundant species, caught in the entrance location mostly between July to November, when water temperature was below 21.5°C. This pattern was consistent across both years. C. leucas, the second most abundant species, were captured in all areas of Sydney Harbour but only in summer and autumn when water temperatures were above 23°C. This study quantified, for this first time, how different species utilise different areas of Sydney Harbour, at different times of the year. This information has implications for the management of human-shark interactions, by enabling creation of education programs to modify human behaviour in times of increased risk of potentially dangerous sharks.

Estimating Finite Rate of Population Increase for Sharks Based on Vital Parameters.

The vital parameter data for 62 stocks, covering 38 species, collected from the literature, including parameters of age, growth, and reproduction, were log-transformed and analyzed using multivariate analyses. Three groups were identified and empirical equations were developed for each to describe the relationships between the predicted finite rates of population increase (λ’) and the vital parameters, maximum age (Tmax), age at maturity (Tm), annual fecundity (f/Rc)), size at birth (Lb), size at maturity (Lm), and asymptotic length (L∞). Group (1) included species with slow growth rates (0.034 yr-1 < k < 0.103 yr-1) and extended longevity (26 yr < Tmax < 81 yr), e.g., shortfin mako Isurus oxyrinchus, dusky shark Carcharhinus obscurus, etc.; Group (2) included species with fast growth rates (0.103 yr-1 < k < 0.358 yr-1) and short longevity (9 yr < Tmax < 26 yr), e.g., starspotted smoothhound Mustelus manazo, gray smoothhound M. californicus, etc.; Group (3) included late maturing species (Lm/L∞ ≧ 0.75) with moderate longevity (Tmax < 29 yr), e.g., pelagic thresher Alopias pelagicus, sevengill shark Notorynchus cepedianus. The empirical equation for all data pooled was also developed. The λ’ values estimated by these empirical equations showed good agreement with those calculated using conventional demographic analysis. The predictability was further validated by an independent data set of three species. The empirical equations developed in this study not only reduce the uncertainties in estimation but also account for the difference in life history among groups. This method therefore provides an efficient and effective approach to the implementation of precautionary shark management measures.

Bioaccumulation of PCBs in liver tissue of dusky Carcharhinus obscurus, sandbar C. plumbeus and white Carcharodon carcharias sharks from south-eastern Australian waters

Polychlorinated biphenyls (PCBs) are ubiquitous pollutants in the marine environment that are known to accumulate in apex predators such as sharks. Liver samples from dusky Carcharhinus obscurus, sandbar Carcharhinus plumbeus, and white Carcharodon carcharias sharks from south-eastern Australian waters were analysed for the seven indicator PCBs 28, 52, 101, 118, 138, 153 and 180. Median ∑PCBs were significantly higher in white than sandbar sharks (3.35 and 0.36μgg−1 lipid, respectively, p=0.05) but there were no significant differences between dusky sharks (1.31μgg−1 lipid) and the other two species. Congener concentrations were also significantly higher in white sharks. Significant differences in PCB concentrations between mature and immature dusky (3.78 and 0.76μgg−1 lipid, respectively) and sandbar (1.94 and 0.18μgg−1 lipid, respectively) sharks indicated that PCB concentrations in these species increased with age/growth. Higher-chlorinated congeners (hexa and heptachlorobiphenyls) dominated results, accounting for ~90% of ∑PCBs.

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.

Characterisation and cross-amplification of 19 novel microsatellite loci for the sandbar shark, Carcharhinus plumbeus

Conservation of vulnerable shark species that are also heavily exploited, such as the sandbar shark Carcharhinus plumbeus is a pressing issue, and molecular genetics is an increasingly important population monitoring and species identification tool. Here we present 19 C. plumbeus microsatellite loci with a broad range of alleles per locus (3–22), and observed heterozygosities (0.17–0.95). Null alleles were not apparent and if present, were at frequencies <0.041. None of the loci showed significant deviation from Hardy–Weinberg equilibrium or indications of linkage disequilibrium. Cross-species amplification of these loci in three other carcharinids, dusky shark Carcharhinus obscurus, spinner shark Carcharhinus brevipinna, and galapagos shark Carcharhinus galapagensis showed polymorphism in 13, 13, and 14 loci respectively. These highly diverse loci will assist both individual-specific and population-wide genetic investigations for these species.

At-vessel and post-release mortality of the dusky (Carcharhinus obscurus) and sandbar (C. plumbeus) sharks after longline capture

Since the mid 1990’s, stock assessments of shark populations in the northwest Atlantic by the National Marine Fisheries Service (NMFS) have indicated that sandbar (Carcharhinus plumbeus) and dusky (C. obscurus) populations are overfished. In response to these assessments, the dusky shark bottom longline fishery was closed in 2000, followed by the sandbar fishery in 2005. A common management strategy is to mandate the release of prohibited species if caught as bycatch. However, a major assumption is that most released sharks survive, which may not be the case. Longline operations were conducted during 2011 and 2012 to capture and tag sandbar and dusky sharks, in order to assess (1) at-vessel mortality, (2) post-release mortality, and (3) investigate the effects of soak-time on each of these variables for each species. Our findings show that dusky sharks experience high at-vessel and post-release mortality, with mortality occurring more frequently after 3–5h on the line. While time-on-the-line (TOL) increased dusky shark at-vessel (16% when less than 3h TOL; 27.5% when more than 3h TOL) and post-release mortality (11% when less than 3h TOL; 42% when more than 3h TOL), sandbar shark at-vessel mortality was low (0% when less than 3h TOL). Nonetheless, the apparently hardier sandbar sharks did exhibit 29% post-release mortality after 3h TOL. The total mortality (at-vessel+post-release, including moribund individuals) for dusky sharks was 97% after being captured on a demersal longline when TOL surpassed 3h. These data clearly elucidate an interspecific difference in vulnerability to longline gear between these species.

It is not just size that matters: shark cruising speeds are species-specific

Speed of locomotion plays an important role in an animal’s biology and ecology and is of particular interest in aquatic animals. Determining cruising speeds of shark—for which such data are scarce—may help to better understand their interactions with prey, the size of the home ranges they maintain, their energetic costs and how they interact with their environment through sensory perception. In this study, the cruising speeds of a range of different shark species were measured using stereo-baited remote underwater video systems (stereo-BRUVS). The relationship between cruising speeds and fork length, species, order, habitat, trophic level, temperature and tail shape was then modelled. Fork length and species best explained the cruising speeds of the eight species of shark studied: Carcharhinus amblyrhynchos, Carcharhinus albimarginatus, Carcharhinus obscurus, Furgaleus macki, Carcharhinus obesus, Mustelus antarcticus, Heterodontus portusjacksoni and Parascyllium variolatum. This linear model had a slope that did not differ statistically from that of the theoretical model proposed by Weihs (Scale effects in animal locomotion, Academic Press, New York, pp 333–338, 1977), which suggests that the relationship between cruising speed and length appears to be dominated by energetics. The results suggest that existing allometric estimates of cruising speeds can be improved by defining cruising speeds for each species as a function of length. Currently, literature presents cruising speed data for only a few species of shark; therefore, we provide a second, generalised model, which predicts cruising speed as a function of length and tail shape. The length + tail shape model was selected based on its generality and accuracy in estimating shark cruising speeds obtained from acoustic tags. This length + tail shape model was significantly better than a length only model; it explained a further 76 % of the variation in cruising speed derived from stereo-BRUVS and acoustic tagging data than a length only model. The more accurate prediction of the length + tail shape model is most likely because tail shape is correlated with a number of ecological factors.

Metal and metalloid concentrations in the tissues of dusky Carcharhinus obscurus, sandbar C. plumbeus and white Carcharodon carcharias sharks from south-eastern Australian waters, and the implications for human consumption

Shark fisheries have expanded due to increased demand for shark products. As long-lived apex predators, sharks are susceptible to bioaccumulation of metals and metalloids, and biomagnification of some such as Hg, primarily through diet. This may have negative health implications for human consumers. Concentrations of Hg, As, Cd, Cu, Fe, Se and Zn were analysed in muscle, liver and fin fibres (ceratotrichia) from dusky Carcharhinus obscurus, sandbar Carcharhinus plumbeus, and white Carcharodon carcharias sharks from south-eastern Australian waters. Concentrations of analytes were generally higher in liver than in muscle and lowest in fin fibres. Muscle tissue concentrations of Hg were significantly correlated with total length, and >50% of sampled individuals had concentrations above Food Standards Australia New Zealand’s maximum limit (1mgkg−1ww). Arsenic concentrations were also of concern, particularly in fins. Results warrant further investigation to accurately assess health risks for regular consumption of shark products.

Age and Growth of the Dusky Shark, Carcharhinus obscurus, in the Western North Pacific Ocean

Age and growth of the dusky shark, Carcharhinus obscurus, in the western North Pacific Ocean was estimated based on 434 specimens (213 females and 256 males) collected between September 2002 and November 2003 at the Nanfanao fish market, in northeastern Taiwan. Sex-specific relationships between body weight (W) and total length (TL) were estimated as follows: W=2.03 × 10^(-6)TL^(3.216) (n=209, p ＜ 0.01) for females and W=8.01 × 10^(-6)TL^(2.957) (n=294, p ＜ 0.01) for males. The relationship between TL and the vertebral centrum radius (R) for both sexes (＂sexes-combined＂ data) was described using the following equation TL=14.74 + 20.31R (n=399, p ＜ 0.01). Growth band pairs (including translucent and opaque bands) in precaudal vertebrae were determined to form once annually, based on centrum edge analysis and verified by statistical analysis. The maximum number of growth band pairs was 29 for females and 24 for males. The Robertson growth function best fit the observed length-at-age data. Sex-specific growth equations were not significantly different; thus, the combined growth parameters for both sexes were estimated as: asymptotic length (L_∞)=369.4 cm TL, b=0.912, growth coefficient (k_R)=0.126 yr-1 (n=385, p ＜ 0.01). Age at maturity was estimated to be 16.6 yrs for females and 15.5 yrs for males.

First observations of dusky sharks (Carcharhinus obscurus) attacking a humpback whale (Megaptera novaeangliae) calf

Direct observations of sharks attacking mysticetes are rare. The present study provides the first direct observation of dusky sharks (Carcharhinus obscurus) attacking a humpback whale (Megaptera novaeangliae) calf. The event was witnessed on 16 July 2014 within the Pondoland Marine Protected Area, South Africa, during the annual sardine run. The event involved a group of ~10 to 20 dusky sharks ranging in length between 2 and 3m. The sharks followed in a loose group behind the whale and attacked it while it was on the surface as well as when diving. Shark bites were concentrated on the left-hand side of the whale’s body primarily between the pectoral fin and tail fluke, with almost no bites on the right-hand side. Most of the bites were superficial and resulted in tooth impressions and scrapes with little tissue removed. The condition of the calf deteriorated over the study period and it was presumed to have drowned from exhaustion when it stopped surfacing. These observations provide a new insight into the potential threat that dusky sharks may pose to whale calves.

English

Experimental gillnetting and setlining provided a detailed account of shark and ray composition at three shallow water sites in Moreton Bay between 2004 and 2007 (n=350 elasmobranchs). The species composition of elasmobranchs significantly differed between sites and shark abundance was highest at the western site (St Helena Island, Waterloo Bay). Juvenile Dusky (Carcharhinus obscurus) and Pigeye Sharks (C. amboinensis) were more abundant at the western site and appear to be rare in the eastern bay. Approximately 8% of the 206 tagged sharks were recaptured, 60% within two kilometres from their release position, with time at liberty ranging from four to 402 days. The results suggest that the documented east-west gradient in teleost diversity in Moreton Bay also extends to the Carcharhinidae. Further research is recommended to determine whether the diversity patterns observed from the three sites are broadly representative of each of these regions. Setlining and rod and line fishing for sharks in a deeper part of the bay between 1978 and 1992 (n=440 elasmobranchs) revealed a different species composition. The Spottail Shark (C. sorrah) and the Spinner Shark (C. brevipinna) comprised 50% and 39% of the catch in this deeper site, respectively, but were rarely caught in shallow regions of the bay, suggesting that the species composition is also partitioned by depth. Western fringes of the bay have been heavily modified by anthropogenic activities and the importance of this area to juvenile whaler sharks needs to be considered. Future sampling at the same fixed locations may provide the opportunity to examine whether recent re-zoning of the Marine Bay Marine Park in 2009, or other factors such as changes in commercial or recreational fishing, have influenced the species composition and abundance of sharks.

Risk assessment of cartilaginous fish populations

Abstract We review three broad categories of risk assessment methodology used for cartilaginous fish: productivity-susceptibility analysis (PSA), demographic methods, and quantitative stock assessments. PSA is generally a semi-quantitative approach useful as an exploratory or triage tool that can be used to prioritize research, group species with similar vulnerability or risk, and provide qualitative management advice. Demographic methods are typically used in the conservation arena and provide quantitative population metrics that are used to quantify extinction risk and identify vulnerable life stages. Stock assessments provide quantitative estimates of population status and the associated risk of exceeding biological reference points, such as maximum sustainable yield. We then describe six types of uncertainty (process, observation, model, estimation, implementation, and institutional) that affect the risk assessment process, identify which of the three risk assessment methods can accommodate each type of uncertainty, and provide examples mostly for sharks drawn from our experience in the United States. We also review the spectrum of stock assessment methods used mainly for sharks in the United States, and present a case study where multiple methods were applied to the same species (dusky shark, Carcharinus obscurus) to illustrate differing degrees of model complexity and type of uncertainty considered. Finally, we address the common and problematic case of data-poor bycatch species. Our main recommendation for future work is to use Management Strategy Evaluation or similar simulation approaches to explore the effect of different sources of uncertainty, identify the most critical data to satisfy predetermined management objectives, and develop harvest control rules for cartilaginous fish. We also propose to assess the performance of data-poor and -rich methods through stepwise model construction.

Isolation and characterization of 20 microsatellite markers from Carcharhinus leucas (bull shark) and cross-amplification in Galeocerdo cuvier (tiger shark), Carcharhinus obscurus (dusky shark) and Carcharhinus plumbeus (sandbar shark)

With the development of genetics methods, it becomes possible to study the population structure and some aspects of the reproductive behaviour of endangered sharks. Here we describe the isolation of 20 polymorphic microsatellite markers in the bull shark Carcharhinus leucas (Carcharhinidae) and their characteristics. Two to 10 alleles per locus were detected. Observed and expected heterozygosities ranged from 0.00 to 0.78 and from 0.05 to 0.80, respectively. Four markers showed deviations from Hardy–Weinberg equilibrium; among them, three showed presence of null alleles. No linkage disequilibrium was detected among any of the loci. Moreover, four, 11 and 19 of these 20 markers successfully cross-amplified in the tiger shark Galeocerdo cuvier, the sandbar shark Carcharhinus plumbeus and the dusky shark Carcharhinus obscurus, respectively.

What barcode sequencing reveals about the shark fishery in Peru

Elasmobranchs are rapidly declining due to overfishing and bycatch, underlining the need for immediate protection. Critical baseline information on the diversity of targeted species is, however, often missing. Peru is a major country for shark fishery, an activity that has been under-regulated and poorly monitored, aggravated by the superficial taxonomic identifications at landing points across the country. Furthermore, most of the species landed by the shark fishery in Peru are listed as Vulnerable in the IUCN Red List. To assess the diversity of shark species targeted by fisheries in Peru we analyzed the variation of the cytochrome oxidase I (cox1) region of the mitochondrial DNA from 118 samples collected between 2004 and 2009, from six landing points. Our analysis revealed unambiguously that the 16 shark species classified by fishermen using meristic characters corresponded only to nine species. While some commonly landed species (e.g. Prionace glauca) were consistently correctly identified, for others species multiple inconsistent names were applied (e.g. Galeorhinus galeus). Our molecular characterization further allowed the identification of specimens with non-informative common names (i.e. “tiburon”=shark). In most cases the unknown specimens were Isurus oxyrinchus and P. glauca. Interestingly, all samples labeled as common thresher (Alopias vulpinus) were identified as pelagic thresher (Alopias pelagicus). Finally, one sample was equivocally identified as a dusky shark (Carcharhinus obscurus) and as a galapagos shark (Carcharhinus galapagensis) reinforcing the genetic similarity reported for these species. We generated a character-based identification library containing 26 of the 31 commercially important sharks landed in Peru and tested its performance as a species diagnostic. The library correctly identified 25 out of 28 barcodes tested, outperforming the distance-based approach. This is the first study sequencing barcodes of marine species in Peru and generated a genetic reference library of targeted shark species. We suggest that the molecular tools used are a quick and effective complement for the monitoring of the fishery of threatened shark species. A combined effort to obtain these data, by countries in the east Pacific region with an on-going shark fishery, would provide with the essential guiding information to promote the implementation of effective sustainable management plans.

Ecological importance of sharks and rays in a structural foodweb analysis in southern Brazil

AbstractUnderstanding the trophic interactions and the position of species within a foodweb is crucial if we want to understand the dynamics of marine communities and the impact individual components of the community have on trophic network compartments. Recent studies have indicated sharks and rays are important elements within foodwebs. In this study, we evaluated the ecological importance of sharks and rays in a subtropical ecosystem off the coast of southern Brazil by using topological analyses. We tested the hypotheses that some elasmobranchs can be considered key elements within the foodweb, and that large predators have topological importance (act as keystones), so that, when large predators are excluded, mesopredator elasmobranchs occupy higher topological positions. Our results indicate that Galeocerdo cuvier, Carcharhinus obscurus, Carcharias taurus, Sphyrna lewini and S. zygaena are species with large ecological function values and may exert a powerful influence over lower levels. These issues need to be considered by conservation and fishery management groups since it appears that ecosystem integrity may be compromised by reductions in the populations of large predators. Carcharhinus obscurus, S. zygaena and Zapteryx brevirostris were found to be the elasmobranchs with largest values of centrality, and can, therefore, be considered key elements in the topological structure.

Habitat, movements and environmental preferences of dusky sharks, Carcharhinus obscurus, in the northern Gulf of Mexico

The dusky shark (Carcharhinus obscurus) is the largest member of the genus Carcharhinus and inhabits coastal and pelagic ecosystems circumglobally in temperate, subtropical and tropical marine waters. In the western North Atlantic Ocean (WNA), dusky sharks are overfished and considered vulnerable by the International Union for the Conservation of Nature. As a result, retention of dusky sharks in commercial and recreational fisheries off the east coast of the United States (US) and in the northern Gulf of Mexico is prohibited. Despite the concerns regarding the status of dusky sharks in the WNA, little is known about their habitat utilization. During the summers of 2008–2009, pop-up satellite archival tags were attached to ten dusky sharks (one male, nine females) at a location where they have been observed to aggregate in the north central Gulf of Mexico southwest of the Mississippi River Delta to examine their movement patterns and habitat utilization. All tags successfully transmitted data with deployment durations ranging from 6 to 124 days. Tag data revealed shark movements in excess of 200 km from initial tagging locations, with sharks primarily utilizing offshore waters associated with the continental shelf edge from Desoto Canyon to the Texas/Mexican border. While most sharks remained in US waters, one individual moved from the northern Gulf of Mexico into the Bay of Campeche off the coast of Mexico. Sharks spent 87 % of their time between 20 and 125 m and 83 % of their time in waters between 23 and 30 °C. Since dusky sharks are among the most vulnerable shark species to fishing mortality, there is a recovery plan in place for US waters; however, since they have been shown to make long-distance migrations, a multi-national management plan within the WNA may be needed to ensure the successful recovery of this population.