ArticleLiterature Review

Recovery potential and conservation options for elasmobranchs

Authors:
  • Fisheries and Oceans Canada - Bedford Institute of Oceanography
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Abstract

Many elasmobranchs have experienced strong population declines, which have been largely attributed to the direct and indirect effects of exploitation. Recently, however, live elasmobranchs are being increasingly valued for their role in marine ecosystems, dive tourism and intrinsic worth. Thus, management plans have been implemented to slow and ultimately reverse negative trends, including shark-specific (e.g. anti-finning laws) to ecosystem-based (e.g. no-take marine reserves) strategies. Yet it is unclear how successful these measures are, or will be, given the degree of depletion and slow recovery potential of most elasmobranchs. Here, current understanding of elasmobranch population recoveries is reviewed. The potential and realized extent of population increases, including rates of increase, timelines and drivers are evaluated. Across 40 increasing populations, only 25% were attributed to decreased anthropogenic mortality, while the majority was attributed to predation release. It is also shown that even low exploitation rates (2-6% per year) can halt or reverse positive population trends in six populations currently managed under recovery plans. Management measures that help restore elasmobranch populations include enforcement or near-zero fishing mortality, protection of critical habitats, monitoring and education. These measures are highlighted in a case study from the south-eastern U.S.A., where some evidence of recovery is seen in Pristis pectinata, Galeocerdo cuvier and Sphyrna lewini populations. It is concluded that recovery of elasmobranchs is certainly possible but requires time and a combination of strong and dedicated management actions to be successful.

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... The regulations intended to protect and manage sharks in recent decades [92] have been ineffective in stopping the decline in their numbers [9,23,25,93]. Listings by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) are proving inadequate in the face of the secretive shark fin trade [6,94]. Protection can only be gained one species at a time, while the shark fin market is indiscriminate, taking fins from essentially any species of shark or ray. ...
... The whale shark, for example, continues to decline in both abundance and size in spite of being protected by the Convention on the Conservation of Migratory Species of Wild Animals 2010 (CMS)-the 'Bonn Convention', CITES, and the Commonwealth Environment Protection and Biodiversity Conservation Act (EPBC) [93]. In 1999 it was listed on Appendix II of the CMS and on Appendix I in 2017 [97]. ...
... In 1999 it was listed on Appendix II of the CMS and on Appendix I in 2017 [97]. Similarly, the sand tiger shark (Carcharias taurus) in southern Australia has been protected from fishing since 1984, but due to the high rate of incidental hooking the population continues to decline [93]. ...
Article
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The expanding shark fin market has resulted in intensive global shark fishing and with 90% of teleost fish stocks over-exploited, sharks have become the most lucrative target. As predators, they have high ecological value, are sensitive to fishing pressure, and are in decline, but the secretive nature of the fin trade and difficulties obtaining relevant data, obscure their true status. In consumer countries, shark fin is a luxury item and rich consumers pay high prices with little interest in sustainability or legal trade. Thus, market demand will continue to fuel the shark hunt and those accessible to fishing fleets are increasingly endangered. Current legal protections are not working, as exemplified by the case of the shortfin mako shark, and claims that sharks can be sustainably fished under these circumstances are shown to be misguided. In the interests of averting a catastrophic collapse across the planet’s aquatic ecosystems, sharks and their habitats must be given effective protection. We recommend that all sharks, chimaeras, manta rays, devil rays, and rhino rays be protected from international trade through an immediate CITES Appendix I listing. However, a binding international agreement for the protection of biodiversity in general is what is needed.
... Elasmobranchs (subclass elasmobranchii)-sharks, rays, and skates (Compagno et al. 2005)-are crucial to aquatic ecosystems, but are currently considered one of the most vulnerable classes of vertebrates and in a global state of decline (Ward-Paige et al. 2012), with nearly a quarter of all species threatened by extinction (Dulvy et al. 2014). Currently, the main threats to elasmobranch populations include overfishing, incidental fishing capture (i.e., bycatch) (Mandelman et al. 2013), and habitat destruction (Ellis et al. 2004), with the latter being increasingly exacerbated by pollution and climate change (Ward-Paige et al. 2012). ...
... Elasmobranchs (subclass elasmobranchii)-sharks, rays, and skates (Compagno et al. 2005)-are crucial to aquatic ecosystems, but are currently considered one of the most vulnerable classes of vertebrates and in a global state of decline (Ward-Paige et al. 2012), with nearly a quarter of all species threatened by extinction (Dulvy et al. 2014). Currently, the main threats to elasmobranch populations include overfishing, incidental fishing capture (i.e., bycatch) (Mandelman et al. 2013), and habitat destruction (Ellis et al. 2004), with the latter being increasingly exacerbated by pollution and climate change (Ward-Paige et al. 2012). Given that most elasmobranchs are apex or meso predators, many are critically important to the health of their respective aquatic ecosystems (White et al. 2012;Hammerschlag et al. 2019), but also provide significant ecosystem services to countries, in the form of revenue and/or sustenance (e.g., eco-tourism and fisheries) (Hammerschlag and Gallagher 2011;Ward-Paige et al. 2012). ...
... Currently, the main threats to elasmobranch populations include overfishing, incidental fishing capture (i.e., bycatch) (Mandelman et al. 2013), and habitat destruction (Ellis et al. 2004), with the latter being increasingly exacerbated by pollution and climate change (Ward-Paige et al. 2012). Given that most elasmobranchs are apex or meso predators, many are critically important to the health of their respective aquatic ecosystems (White et al. 2012;Hammerschlag et al. 2019), but also provide significant ecosystem services to countries, in the form of revenue and/or sustenance (e.g., eco-tourism and fisheries) (Hammerschlag and Gallagher 2011;Ward-Paige et al. 2012). ...
Article
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The consequences of human influence can arise in vertebrates as primary, secondary, or even tertiary stressors and may be especially detrimental for slow growing species with long generation times (i.e., K-selected species). Here, we review the impacts of both direct and indirect human interactions on the reproductive biology of elasmobranchs. Within direct human influence, capture-induced stress from fisheries bycatch and poor coastal management practices leading to habitat destruction and pollution are among the most impactful on elasmobranch reproduction. Capture-induced stress has been shown to negatively influence offspring and reproductive capacity via capture-induced parturition as well as by disrupting the reproductive physiology of adults. Habitat degradation impacts essential ecosystems that are necessary for the development of young elasmobranchs. Pollutants such as heavy metals, legacy pesticides, and flame retardants have been traced through elasmobranch reproduction; however, the long-term effects of these exogenous chemicals are yet to be determined. Furthermore, within indirect human impacts, climate change-mediated influences (e.g., ocean warming and acidification) can impact development, physiological processes, and behavioral patterns necessary for essential tasks such as foraging, growth, reproduction, and ultimately survival. Here, we also present a case study, where data regarding temperature and incubation time from 28 egg-laying elasmobranch species were examined to show relevance of such data in predicting how suitable (e.g., via maximum threshold temperatures) habitats will be for skate and shark development in the coming century. Concomitantly, this information highlights areas for future research that will help inform better management as well as climate change forecasting for this threatened group of aquatic vertebrates.
... Shark populations worldwide are declining due to direct and indirect effects of fishing (Baum et al. 2010;Davidson et al. 2016). With life history traits such as slow growth, late maturity, low fecundity and long gestation periods, sharks are particularly susceptible to overexploitation and have low potential for population recovery (Ward-Paige et al. 2012). The highly mobile and often elusive nature of elasmobranchs impedes investigations into issues relevant to conservation and fisheries management, such as population structure, demographic trends and migration patterns. ...
... This is particularly true when the re-establishment through straying individuals is too slow to be effective on ecological timescales . In large sharks such as C. taurus, this problem would be exacerbated by the fact that population recovery is slow because of a long generation time and low fecundity (Musick 1999;Ward-Paige et al. 2012;Hutchings et al. 2014). The evidence for the existence of genetically differentiated nursery areas suggests that the South African population of C. taurus would risk losing much of its genetic diversity if adult females that have returned to their natal sites to pup, or their younger offspring, were to be overfished in any of the five nursery areas. ...
Article
Full-text available
The cosmopolitan lamniform shark Carcharias taurus (commonly known as the ragged-tooth, grey nurse or sand tiger shark) is threatened by overexploitation in parts of its range. Return migrations of females to specific nursery areas suggest that females exhibit reproductive philopatry, a behaviour that over time might lead to genetically isolated subpopulations over various spatial scales. To investigate genetic evidence for reproductive philopatry, genetic data from mitochondrial and microsatellite markers were generated for 104 young-of-the-year and juvenile sharks. Comparing the smallest versus the largest young sharks revealed a pattern of size-related differentiation between nurseries that was only found in the smaller size class. This not only confirms reproductive philopatry of their mothers, but is also in line with previous observations of larger juvenile sharks increasing their migration range and moving between sites. Our results highlight the need to target young-of-the-year sharks when investigating reproductive philopatry to exclude roaming individuals that obscure size-related signals of genetic differentiation. Given the species’ high susceptibility to overexploitation, the evidence for reproductive philopatry is of direct importance to the management and conservation of C. taurus worldwide. As many nursery areas as possible should be protected to ensure that the number of locally resident juveniles and the pool of the returning females remain stable in the long term. This may warrant protected areas, or time-area closures, prohibiting exploitation in the nursery areas during pupping season.
... Currently about ¼ of all sharks, rays and skates are facing an elevated extinction risk, primarily because of their overexploitation from fisheries [1]. Due to that, global public awareness and perception of elasmobranchs, especially sharks, is gradually shifting towards their conservation rather than exploitation [2]. Paradoxically at the same time, the demand for elasmobranch products is still rising [3,4]. ...
... Paradoxically at the same time, the demand for elasmobranch products is still rising [3,4]. In 2011 global shark fisheries value was estimated around 1$ US billion [1], excluding the value of elasmobranch products consumed domestically, which may potentially comprise the vast majority of the captures (around 2 million tons) [1], as well as the Illegal, Unreported and Unregulated (IUU) portion of the catches [2]. Thus, official data may underestimate the total commercial harvests and misrepresent the current level of shark exploitation. ...
Article
Elasmobranchs, extremely charismatic and threatened animals, still are an important economic source for fshers in many parts of the world, providing signifcant income through trade. Even though Greek seas host at least 67 elasmobranch species, our knowledge about their biology and ecology is to a large extent unknown. In the present study the integration of conventional (legislation, offcial data from fsheries landings and fsh market value and import/export data) and unconventional (social media) sources of data, accompanied with the use of genetics, aim at outlining the elasmobranch fsheries and trade in Greece and identifying “weak spots” that sabotage their conservation. Results revealed that: (a) about 60% of the 68 specimens collected in fsh markets were mislabelled, with that being very common for Prionace glauca and Mustelus spp., (b) Illegal fshing is a reality, c) Greece represents one of the top-three European Union southern countries in terms of elasmobranch market size, (d) Aegean Sea and especially its Northern part (Thermaikos Gulf and Thracian Sea) contributed to more than half of the M. mustelus Greek fsheries landings and (e) wholesale prices of elasmobranchs have remained stable during the last decade. Mislabelling and illegal trade of elasmobranchs are common ground in Greece. This context stems from incoherent and complex fsheries legislative framework due to institutional decoupling, discrepancies in the collection and analysis of fsheries-related data, thus substantially reducing the effciency of the fsheries management in Greek seas.
... Spatial closures, such as marine protected areas (MPAs) and no take marine reserves as well as fishing bans are some of the fisheries management strategies that have been implemented to slow and reverse the effect of large-scale overfishing on shark populations (Ward-Paige et al., 2012). ...
... Fishers and traders would mostly turn to non-fishing related livelihood activities, which include small business, transportation and artisanships as fallback livelihood options should there be a moratorium on shark fisheries. Restriction of fishers from shark fisheries may reduce fishing pressure, in the light of declining shark stocks (Ward- Paige et al., 2012). However, this study also revealed that a significant number of fishers would simply switch to target other marine fish resources. ...
Preprint
Full-text available
Small-scale shark fisheries support a large number of coastal community livelihoods in developing countries. Shark meat comprises a cheap source of protein and is traded locally in many parts in developing countries, while the skins, oil, fins and gill rakers are exported to the international market. This study addresses a gap in literature regarding the importance of elasmobranchs to key shark-fishing communities and the degree to which trade in shark products (meat and fins) vary in time and among fishing communities in Ghana. We interviewed 85 fishers and traders involved in shark fisheries in Axim, Dixcove, and Shama communities using semi-structured questionnaires. Fishing was the primary source of income and accounted for 59.9% of the total household income of respondents. Other important economic activities were fish processing (15.2%), fish retailing (14.8%), and small businesses (2.9%). One-third and often two-thirds of respondents generated between 80-100% of their income from shark fisheries: Axim (n = 65%), Dixcove (68%), and Shama (35%). Shark meat consumption was common among fishers and traders and represents a substantial source of protein in the diet of the study communities. Overexploitation of these species may compromise food security. Hammerhead Sharks (Sphyrna spp) and Bull Shark (Carcharhinus leucas) have the most valuable fins and meat. Further, 75% and 95% of fishers and traders respectively see fishing and trading of shark meat as their last safety-net and, therefore, tend to be satisfied with their jobs. Non-fishing related livelihood streams including small businesses and transportation were the major fallback activities both fishers and traders preferred to rely on if there is a ban on the exploitation of sharks in Ghana. Thus, any shark management strategy must take into consideration the preferred livelihood fallback options outlined by fishers and traders, and implement them to ensure the success of the intervention.
... Shark and Ray fish caught by local fishermen in Diani Landing Site, Kenya (Source: Prisca Rael Auma) Furthermore, even though the extent and effects are blurred, there exists a poaching and population decline of elasmobranchs in protected areas that are open to vessels (Cowburn et al., 2018), equated to greater elasmobranch abundance in no-entry zones (Ward-Paige et al., 2012). This highlights the importance of enforcements and public support for the success of protected areas in protecting elasmobranchs populations.In Kenya artisanal fishermen use the oil from whale shark liver to cure their vessels from rot (Pine et al., 2007). ...
... Being a fisheries management tool (Lundquist & Granek, 2005), MPA authorities will have to work together with fishers through negotiation process since conservation success of elasmobranchs is based on local stakeholders (Noriega et al., 2012). This will encourage public participation in scientific monitoring (Ward-Paige et al., 2012). Interest and support of stakeholders groups can contribute to both short-and long-term success of MPA (Lundquist & Granek, 2005). ...
Technical Report
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Let us SAVE Sharks and Ray Fish from Kenya to the world
... Given our increasing human population causing growing pressures on our natural resources (Lotze, 2006), the implementation and monitoring of management measures are of ever greater importance (Hutchings and Reynolds, 2004;Ward-Paige et al., 2012). However, the effectiveness of management measures is rarely evaluated in the context of other factors that may affect populations. ...
... In particular, our results suggest that protecting juveniles through measures such as minimum landing sizes and nursery areas could have important benefits to species survival. Brander (1981) and Ward-Paige et al. (2012) came to similar conclusions regarding the importance of juvenile survival to elasmobranch population recovery. ...
Article
Global declines in elasmobranchs have been observed. Conservation measures such as area closures and fisheries prohibitions have been put in place to support the recovery of vulnerable species. However, the effectiveness of such measures is rarely evaluated in the context of other factors that may affect population abundance. This study investigates the effectiveness of management measures using 1) General additive mixed model derivative changes, taking into account environmental factors that may affect population stochasticity and 2) an age-structured density dependent population dynamic model. The Raja undulata (undulate ray) 2009 targeted fisheries prohibition was used as a case study. Potential beneficial responses on sympatric species Raja clavata (thornback ray) were modelled. A significant increase in abundance was observed in both IUCN red list species during the ban. Surface seawater temperature had a marginal effect on the abundance of both species. The prohibition was in place for an insufficient length of time for long lasting effects to be detected on skate length. The population dynamic model indicated that the increase in abundance was only possible when combining the fisheries ban with increased juvenile discard survival. Our results indicate that species conservation measures may not only have positive effects on the species in question, but also on species with a niche overlap. Nonetheless, due to ongoing fishing for other species, the full potential of fisheries prohibitions may not be realised. For real benefits to be assessed, evaluation of bans should take place once a steady state is observed.
... As part of the overall marine biodiversity, these species contribute to the control of prey populations, as well as the overall stability and recovery of marine habitats [23][24][25][26]. Their life history traits which often entail late maturity, long gestation times, and few offspring, expose them to an elevated risk to fishing [27,28] and other human related pressures, such as pollution, habitat degradation and expedited climate change [29][30][31][32][33]. Therefore, they rely on sustainable management and conservation efforts for future existence [34][35][36]. This is especially the case in the Mediterranean, where more than half of the occurring elasmobranch species face elevated risks of extinction and continued to decline in the past decades [37]. ...
... In view of the biological traits of elasmobranchs, recovery can take decades and therefore, a stronger precautionary approach and foresight to the conservation and management of these species, which are subject to fisheries' pressures, would seem preferable [147]. Legal protection alone does not guarantee effective conservation, and in order for fisheries to be sustainable, specific, wide-ranging measures have to be implemented, enforced, and monitored [35]. ...
Article
This study examined the integration and application of the precautionary principle at national level for the conservation and management of elasmobranchs. Three countries, Greece, Malta, and Cyprus were assessed. Based on national legislation, policies, and reports, the assessment shows limited integration and application of the precautionary approach for the conservation and management of this group. The review of existing measures and relevant literature revealed potential applications of the precautionary principle for two model species, the blue shark (Prionace glauca) and the bull ray (Aetomylaeus bovinus). Sixteen measures, ranging from basic to strong precautionary actions, are proposed to aid the conservation and management of these two species.
... This species was once also common in the Bay of Biscay (Quéro & Cendrero, 1996). Globally, predation release seems to have been an important driver for increases in certain skate species, with reduced fishing mortality playing a smaller role (see review in Ward-Paige, Keith, Worm and Lotze (2012)). ...
... Predation release is another factor that has been used to explain community changes (Myers, Baum, Shepherd, Powers & Peterson, 2007;Shepherd & Myers, 2005;Ward-Paige et al., 2012). Several large elasmobranch species have declined in the Bay of Biscay, including S. squatina (Quéro & Cendrero, 1996), D. batis complex and R. alba. ...
Article
Sustainable fisheries management requires assessing exploited populations and communities. Traditional fisheries stock assessment methods need species-specific input data, which for skates have become available only recently in Europe. To overcome this limitation, a Bayesian multispecies biomass production model was developped. In addition to aggregated landings, the input data are short time series with species-specific information (landings and biomass indices). Applying the approach to four main skate species and a group of two skate species all managed together in the Bay of Biscay (Northeast Atlantic), long-term changes in the skate assemblage composition were identified. Since the 1990s, Leucoraja naevus became increasingly dominant, while the contributions of the other three species (Raja brachyura, Raja clavata and Raja montagui) declined. The abundance of the grouped Leucoraja fullonica and L. circularis has also strongly decreased, suggesting long-term overexploitation. All species except this species group are expected to increase over the next decade under current harvest rates. Currently the species considered here are managed under a single fishing quota making it unlikely that the group of the two most depleted species will recover soon. The multispecies modelling approach bears promise for other harvested assemblages for which only grouped harvest information is available for certain periods.
... Long-lived, migratory species may be particularly at risk of extinction (Hutchings et al., 2012;Lewison et al., 2004) because they are likely to encounter diverse threats over a lifetime (Lascelles et al., 2014). Such species require longterm international conservation management, which is usually most successful when informed by an understanding of specific life-history traits and their variation (Dulvy et al., 2014;Ward-Paige et al., 2012). ...
... For Mediterranean loggerhead and green turtles, we reiterate the acute need to address anthropogenic mortality rates as a priority to increase survival of post-pelagic individuals (Casale and Heppell, 2016;Casale, 2011;Levy et al., 2015;Snape et al., 2013;Wallace et al., 2008). While increasing reproductive success is undeniably essential for some conservation-dependent species, increasing survival across all age classes, and particularly for juvenile life stages, would have the most profound impact on population growth rates for sea turtles and other long-lived marine vertebrates (Cortés, 2002;Halley, Van Houtan, and Mantua, 2018;Ward-Paige et al., 2012). ...
Article
Full-text available
Estimating life‐history traits and understanding their variation underpins the management of long‐lived, migratory animals, while knowledge of recovery dynamics can inform the management of conservation‐dependent species. Using a combination of nest counts and individual‐based life‐history data collected since 1993, we explore the drivers underlying contrasting population recovery rates of sympatrically nesting loggerhead (Caretta caretta) and green (Chelonia mydas) turtles in North Cyprus. We found that nest counts of loggerhead and green turtles from 28 beaches across the island increased by 46% and 162%, respectively over the past 27 years. A Bayesian state‐space model revealed that, at our individual‐based monitoring site, nesting of green turtles increased annually at four times the rate of that of loggerhead turtles. Furthermore, we found that loggerhead turtles nesting at the individual‐based monitoring site had stable reproductive parameters and average adult survival for the species and are the smallest breeding adults globally. Based on results from multiple matrix model scenarios, we propose that higher mortality rates of individuals in all age classes (likely driven by differences in life history and interaction with fisheries), rather than low reproductive output, are impeding the recovery of this species. While the increase in green turtles is encouraging, the Mediterranean population is estimated to have around 3,400 adults and is restricted to the Eastern Basin. The recovery of loggerhead turtles is likely to be compromised until mortality rates in the region are adequately quantified and mitigated. As survival of immature individuals is a powerful driver for sea turtle population numbers, additional efforts should target management at pelagic and neritic foraging areas. Understanding threats faced by immature life stages is crucial to accurately parameterise population models and to target conservation actions for long‐lived marine vertebrates. This paper uses 27 years of data to investigate the long‐term population trends of green and loggerhead turtles in North Cyprus and explores drivers of the different recovery patterns observed for the two species. Nest counts of loggerhead and green turtles from 28 beaches increased by 46% and 162%, respectively. A Bayesian state space model revealed that, at the individual‐based monitoring site, the number of nesting green turtles increased annually at four times the rate of that of loggerhead turtles. Based on results from multiple matrix model scenarios, we propose that higher mortality rates of individuals in all age‐classes (likely driven by greater interaction with fisheries), rather than low reproductive output, are impeding the recovery of loggerhead turtles. The species’ recovery is likely to be compromised until mortality rates in the region are adequately quantified and mitigated. Photo credit: Tevfik Camgoz
... This uncertainty is largely due to the ubiquitous nature of fishing in coral reef ecosystems worldwide (Newton et al., 2007). These issues are pertinent to the establishment of management strategies such as marine protected areas (MPAs) (Bond et al., 2012;White et al., 2017) and shark sanctuaries (Ward-Paige et al., 2012) that have been promoted as a means of ensuring the conservation and recovery of shark populations. They add to other unanswered questions about this approach to management and its efficacy (Davidson, 2012), such as the optimal size and placement of MPAs, whether they are useful for all components of a shark fauna including wide-ranging apex predators (Ward-Paige et al., 2012) and mesopredators (White et al., 2017), and the level of enforcement that is required to have desired effects for shark populations (Ward-Paige, 2017). ...
... These issues are pertinent to the establishment of management strategies such as marine protected areas (MPAs) (Bond et al., 2012;White et al., 2017) and shark sanctuaries (Ward-Paige et al., 2012) that have been promoted as a means of ensuring the conservation and recovery of shark populations. They add to other unanswered questions about this approach to management and its efficacy (Davidson, 2012), such as the optimal size and placement of MPAs, whether they are useful for all components of a shark fauna including wide-ranging apex predators (Ward-Paige et al., 2012) and mesopredators (White et al., 2017), and the level of enforcement that is required to have desired effects for shark populations (Ward-Paige, 2017). It is generally agreed that strict enforcement is paramount to the success of an MPA Dulvy, 2006;Edgar et al., 2014;Gill et al., 2017), although even well-managed parks such as the Great Barrier Reef Marine Park have seen declines in common species of reef sharks due to illegal fishing in no-take zones . ...
Preprint
There is limited evidence on the rate at which the shark populations of coral reefs can rebound from over-exploitation, the baselines that might signify when recovery has occurred and the role of no-take Marine Protected Areas (MPA) in aiding this process. We surveyed shark assemblages at Ashmore Reef in Western Australia using baited remote underwater video stations in 2004 prior to enforcement of MPA status and then again in 2016 after eight years of strict enforcement. We found an increase in the relative mean abundance of Carcharhinus amblyrhynchos from 0.16 ± 0.06 individuals h−1 in 2004 to 0.74 ± 0.11 individuals h−1 in 2016, a change that was also accompanied by a shift in the assemblage of sharks to greater proportions of apex species (from 7.1% to 11.9%) and reef sharks (from 28.6% to 57.6%), and a decrease in the proportional abundance of lower trophic level species (from 64.3% to 30.5%). Abundances and trophic assemblage of sharks at Ashmore Reef in 2004 resembled those of the Scott Reefs, where targeted fishing for sharks still occurs, whereas in 2016, abundances and trophic structures had recovered to resemble those of the Rowley Shoals, a reef system that has been a strictly enforced MPA for over 25 years. The shift in abundance and community structure coincident with strict enforcement of the MPA at Ashmore Reef has occurred at a rate greater than predicted by demographic models, implying the action of compensatory processes in recovery. Our study shows that shark communities can recover rapidly after exploitation in a well-managed no-take MPA.
... While shark fins are considered to be one of the most valuable products in the ocean (Gallagher and Hammerschlag, 2011), shark meat often attains only 20-60% of the price of tuna and mackerel meat (Bonfil, 1994). As a result, captured individuals usually have their fins removed for the shark fin market, the head is discarded, and the remaining central body part ("cigar") is then sold for the shark meat market with no special care (Kotas et al., 2008;Ward-Paige et al., 2012). From a taxonomic point of view, the removal of the head and fins represents a challenge to reliable species identification based on morphological features, allowing shark carcasses to be traded fraudulently (Holmes et al., 2009). ...
... For the remaining samples, we used a protocol based on the CTAB method (Doyle, 1987). We used the COI primers FishF2 (5 ′ TCG ACT AAT CAT AAA GAT ATC GGC AC 3 ′ ) and FishR2 (5 ′ ACT TCA GGG TGA CCG AAG AAT CAG AA 3 ′ ) (Ward et al., 2005). Amplification reactions were prepared with 0.4 µM of each dNTP, 1.5 mM MgCl 2 , 0.5 µM of each primer, 1 U Taq Polymerase, and ∼40 ng of genomic DNA. ...
Article
Full-text available
Elasmobranchs, the group of cartilaginous fishes that include sharks and rays, are especially vulnerable to overfishing due to low fecundity and late sexual maturation. A significant number of elasmobranch species are currently overexploited or threatened by fisheries activities. Additionally, several recent reports have indicated that there has been a reduction in regional elasmobranch population sizes. Brazil is an important player in elasmobranch fisheries and one of the largest importers of shark meat. However, carcasses entering the shark meat market have usually had their fins and head removed, which poses a challenge to reliable species identification based on the morphology of captured individuals. This is further complicated by the fact that the internal Brazilian market trades several different elasmobranch species under a common popular name: “cação.” The use of such imprecise nomenclature, even among governmental agencies, is problematic for both controlling the negative effects of shark consumption and informing the consumer about the origins of the product. In this study, we used DNA barcoding (mtDNA, COI gene) to identify, at the species level, “cação” samples available in local markets from Southern Brazil. We collected 63 samples traded as “cação,” which we found to correspond to 20 different species. These included two teleost species: Xiphias gladius (n = 1) and Genidens barbus (n = 6), and 18 species from seven elasmobranch orders (Carcharhiniformes, n = 42; Squaliformes, n = 3; Squatiniformes, n = 2; Rhinopristiformes, n = 4; Myliobatiformes, n = 3; Rajiformes, n = 1; and Torpediniformes, n = 1). The most common species in our sample were Prionace glauca (n = 15) and Sphyrna lewini (n = 14), while all other species were represented by four samples or less. Considering IUCN criteria, 47% of the elasmobranch species found are threatened at the global level, while 53% are threatened and 47% are critically endangered in Brazil. These results underline that labeling the meat of any shark species as “cação” is problematic for monitoring catch allocations from the fishing industry and discourages consumer engagement in conservationist practices through informed decision-making.
... This uncertainty is largely due to the ubiquitous nature of fishing in coral reef ecosystems worldwide (Newton et al., 2007). These issues are pertinent to the establishment of management strategies such as marine protected areas (MPAs) (Bond et al., 2012;White et al., 2017) and shark sanctuaries (Ward-Paige et al., 2012) that have been promoted as a means of ensuring the conservation and recovery of shark populations. They add to other unanswered questions about this approach to management and its efficacy (Davidson, 2012), such as the optimal size and placement of MPAs, whether they are useful for all components of a shark fauna including wide-ranging apex predators (Ward-Paige et al., 2012) and mesopredators (White et al., 2017), and the level of enforcement that is required to have desired effects for shark populations (Ward-Paige, 2017). ...
... These issues are pertinent to the establishment of management strategies such as marine protected areas (MPAs) (Bond et al., 2012;White et al., 2017) and shark sanctuaries (Ward-Paige et al., 2012) that have been promoted as a means of ensuring the conservation and recovery of shark populations. They add to other unanswered questions about this approach to management and its efficacy (Davidson, 2012), such as the optimal size and placement of MPAs, whether they are useful for all components of a shark fauna including wide-ranging apex predators (Ward-Paige et al., 2012) and mesopredators (White et al., 2017), and the level of enforcement that is required to have desired effects for shark populations (Ward-Paige, 2017). It is generally agreed that strict enforcement is paramount to the success of an MPA Dulvy, 2006;Edgar et al., 2014;Gill et al., 2017), although even well-managed parks such as the Great Barrier Reef Marine Park have seen declines in common species of reef sharks due to illegal fishing in no-take zones . ...
Article
There is limited evidence on the rate at which the shark populations of coral reefs can rebound from over-exploitation, the baselines that might signify when recovery has occurred and the role of no-take Marine Protected Areas (MPA) in aiding this process. We surveyed shark assemblages at Ashmore Reef in Western Australia using baited remote underwater video stations in 2004 prior to enforcement of MPA status and then again in 2016 after eight years of strict enforcement. We found an increase in the relative mean abundance of Carcharhinus amblyrhynchos from 0.16 ± 0.06 individuals h−1 in 2004 to 0.74 ± 0.11 individuals h−1 in 2016, a change that was also accompanied by a shift in the assemblage of sharks to greater proportions of apex species (from 7.1% to 11.9%) and reef sharks (from 28.6% to 57.6%), and a decrease in the proportional abundance of lower trophic level species (from 64.3% to 30.5%). Abundances and trophic assemblage of sharks at Ashmore Reef in 2004 resembled those of the Scott Reefs, where targeted fishing for sharks still occurs, whereas in 2016, abundances and trophic structures had recovered to resemble those of the Rowley Shoals, a reef system that has been a strictly enforced MPA for over 25 years. The shift in abundance and community structure coincident with strict enforcement of the MPA at Ashmore Reef has occurred at a rate greater than predicted by demographic models, implying the action of compensatory processes in recovery. Our study shows that shark communities can recover rapidly after exploitation in a well-managed no-take MPA.
... The performance of management actions aimed at averting decline should also be assessed by monitoring population trends (e.g. Ward-Paige et al. 2012). Monitoring data will be most useful when it covers sufficient spatial and temporal scales to estimate trends accurately with respect to the IUCN criteria for red listing. ...
Preprint
Full-text available
The assessment of the conservation status of wide ranging species depends on estimates of the magnitude of their population trends. The accuracy of trend estimates will depend on where and how many locations within a species’ range are sampled. We ask how the spatial extent of sampling interacts with non-linear patterns in long-term trends to affect estimates of decline in standardised catch of tiger sharks ( Galeocerdo cuvier ) on the east coast of Australia. We apply a Bayesian trend model that uses prior information on life-history traits to estimate trends where we use data from all regions versus spatial subsets of the data. As more regions were included in the model the trend estimates converged towards an overall decline of 71% over three generations. Trends estimated from data only from northern regions or southern regions underestimated and overestimated the regional decline, respectively. When a subset of regions was modelled, rather than the full data-set, the prior informed by life-history traits performed well, as did a weakly informed prior that allowed for high variation. The rate of decline in tiger sharks is consistent with a listing East Coast Australia tiger sharks as endangered under local legislation. Monitoring programs that aim to estimate population trends should attempt to cover the extremes and mid-points of a population’s range. Life-history information can be used to inform priors for population variation and may give more accurate estimates of trends that can be justified in debates about the status of threatened species, particularly when sampling is limited.
... A recent review showed that only 47 chondrichthyans (shark, batoids, and chimeras) have had stock assessments, and of those, 33 species are considered to be fished sustainably; this represents only a small percentage ($2.6%) of global shark diversity (n ¼ 1188 species). That review also showed that while species with relatively low productivitysee estimates of various rates of population change (r, r max , and k) (McAuley et al., 2007;Dulvy et al., 2008;Smith et al., 2008;Romine et al., 2009;Ward-Paige et al., 2012;Liu et al., 2015;Cortés, 2016)-can support sustainable fisheries (e.g. school sharks), no species with a maximum rate of population increase (r max < 0.1) were identified as sustainable. ...
Article
Full-text available
Effective fisheries management generally requires reliable data describing the target species’ life-history characteristics, the size of its harvested populations, and overall catch estimates, to set sustainable quotas and management regulations. However, stock assessments are often not available for long-lived marine species such as sharks, making predictions of the long-term population impacts of variable catch rates difficult. Fortunately, stage- or age-structured population models can assist if sufficient information exists to estimate survival and fertility rates. Using data collected from the bronze whaler (Carcharhinus brachyurus) fishery in South Australia as a case study, we estimated survival probabilities from life tables of harvested individuals, as well as calculated natural mortalities based on allometric predictions. Fertility data (litter size, proportion mature) from previous studies allowed us to build a fertility vector. Deterministic matrices built using estimates of life-table data or natural mortality (i.e., harvested-augmented and natural mortality) produced instantaneous rates of change of 0.006, and 0.025, respectively. Assuming an incrementing total catch at multiples of current rates, stochastic simulations suggest the relative rate of population decline starts to become precipitous around 25% beyond current harvest rates. This is supported by a sharp increase in weighted mean age of the population around 25% increase on current catches. If the catch is assumed to be proportional (i.e., a constant proportion of the previous year’s population size), the relative r declines approximately linearly with incrementing harvest beyond the current rate. A global sensitivity analysis based on a Latin-hypercube sampling design of seven parameters revealed that variation in the survival estimates derived from the life tables was by far the dominant (boosted-regression tree relative influence score = 91.14%) determinant of model performance (measured as variation in the long-term average rate of population change r). While current harvest rates therefore appear to be sustainable, we recommend that fisheries-management authorities attempt to sample a broader size range of individuals (especially older animals) and pursue stock assessments. Our models provide a framework for assessing the relative susceptibility of long-lived fishes to harvest pressure when detailed stock data are missing.
... For harvested species, it is critical to evaluate a species' potential to be fished sustainably . From a science-based management perspective, this would require knowledge of the biology, ecology, physiology and fisheries of a species (Ward-Paige et al. 2012;Shiffman and Hammerschlag 2016). In southern Africa, chondrichthyans (sharks, skates, rays and chimaeras) are captured in several types of commercial fisheries, but owing to a combination of low product value, species misidentification and harvesting by more than one fishery, management and research efforts remain confounded (Bester-van der da Silva et al. 2015). ...
Article
Full-text available
The blacktip shark Carcharhinus limbatus is a cosmopolitan species found in warm-temperate, subtropical and tropical waters around the world. The research here aimed to assess whether multiple paternity exists in South African C. limbatus and to confirm phylogeographic patterns previously observed within the species. A minimum and maximum frequency of 50% and 71% multiple paternity, respectively, were observed in 14 litters genotyped with five microsatellite markers. Based on the mitochondrial control region, relatively high nucleotide and haplotype diversity characterised the South African sampling population, and pairwise φST values indicated that it significantly differed from the populations of the Pacific and the western Atlantic oceans. The haplotype network showed that the South African samples were grouped closely with the Australian, Indo-Pacific and West African C. limbatus samples, which is suggestive of an Indo-Pacific origin for this population. This study is the first to report multiple paternity in this species. Furthermore, the results reveal that C. limbatus from South Africa is genetically diverse and phylogeographically distinct from most other C. limbatus populations.
... The performance of management actions aimed at averting decline should also be assessed by monitoring population trends (e.g. Ward-Paige et al., 2012). Monitoring data will be most useful when it covers sufficient spatial and temporal scales to estimate trends accurately. ...
... Sharks and their cartilaginous relatives (Class Chondrichthyes, herein 'sharks') are one of the world's most threatened species groups (Dulvy et al., 2014). This is primarily due to overfishing, with high levels of fishing mortality and conservative life-history traits that make many species intrinsically vulnerable to overexploitation (Stevens et al., 2000;Ward-Paige et al., 2012;Worm et al., 2013). Fishing pressure is driven in part by growing international demand for shark-derived commodities (most notably fins, but also meat, cartilage, liver oil), which creates a high market value for sharks. ...
... A recent review showed that only 47 chondrichthyans (shark, batoids, and chimeras) have had stock assessments, and of those, 33 species are considered to be fished sustainably; this represents only a small percentage ($2.6%) of global shark diversity (n ¼ 1188 species). That review also showed that while species with relatively low productivitysee estimates of various rates of population change (r, r max , and k) (McAuley et al., 2007;Dulvy et al., 2008;Smith et al., 2008;Romine et al., 2009;Ward-Paige et al., 2012;Liu et al., 2015;Cortés, 2016)-can support sustainable fisheries (e.g. school sharks), no species with a maximum rate of population increase (r max < 0.1) were identified as sustainable. ...
Article
Effective fisheries management generally requires reliable data describing the target species' life-history characteristics, the size of its harvested populations, and overall catch estimates, to set sustainable quotas and management regulations. However, stock assessments are often not available for long-lived marine species such as sharks, making predictions of the long-term population impacts of variable catch rates difficult. Fortunately, stage-or age-structured population models can assist if sufficient information exists to estimate survival and fertility rates. Using data collected from the bronze whaler (Carcharhinus brachyurus) fishery in South Australia as a case study, we estimated survival probabilities from life tables of harvested individuals, as well as calculated natural mortalities based on allometric predictions. Fertility data (litter size, proportion mature) from previous studies allowed us to build a fertility vector. Deterministic matrices built using estimates of life-table data or natural mortality (i.e. harvested-augmented and natural mortality) produced instantaneous rates of change of 0.006 and 0.025, respectively. Assuming an incrementing total catch at multiples of current rates, stochastic simulations suggest the relative rate of population decline starts to become precipitous around 25% beyond current harvest rates. This is supported by a sharp increase in weighted mean age of the population around 25% increase on current catches. If the catch is assumed to be proportional (i.e. a constant proportion of the previous year's population size), the relative r declines approximately linearly with incrementing harvest beyond the current rate. A global sensitivity analysis based on a Latin-hypercube sampling design of seven parameters revealed that variation in the survival estimates derived from the life tables was by far the dominant (boosted-regression tree relative influence score ¼ 91.14%) determinant of model performance (measured as variation in the long-term average rate of population change r). While current harvest rates therefore appear to be sustainable, we recommend that fisheries-management authorities attempt to sample a broader size range of individuals (especially older animals) and pursue stock assessments. Our models provide a framework for assessing the relative susceptibility of long-lived fishes to harvest pressure when detailed stock data are missing.
... The conversation on how best to approach the management and conservation of vulnerable sharks and rays is a globally recognized challenge (Clarke, 2013;Dulvy et al., 2017;Shiffman, 2016;Ward-Paige, Keith, Worm, & Lotze, 2012), and part of a wider discussion on the state of global fisheries (Pauly, Christensen, Dlasgaard, Froese, & Torres, 1998;Worm et al., 2006;vs. Hampton, Sibert, Kleiber, Maunder, & Harley, 2005;Hilborn, 2006;Murawski, Methot, & Tromble, 2007). ...
Article
International trade in vulnerable marine species is regulated once they are listed in CITES Appendices (the Convention on International Trade in Endangered Species of Wild Fauna and Flora). Parties to the Convention submit proposal(s) 150 days prior to the CITES Conference for voting on the inclusion of new species in Appendices I and II, making a case for why CITES listing criteria are met in each case. Before the vote, Parties receive advice from (a) the Food and Agriculture Organization of the United Nations, (b) the International Union for Conservation of Nature—TRAFFIC and (c) the CITES Secretariat, among others. This paper offers an expert review of listing processes, which are the subject of much debate in fishery and environment‐protection communities, looking at two specific cases: silky shark (Carcharhinus falciformis, Carcharhinidae) and bigeye thresher shark (Alopias superciliosus, Alopiidae). The reviewers determine that the evidence made available to voting Parties is substantial, but suffers from non‐standard presentation across assessments. The best available data are not always presented or described transparently in relation to CITES criteria. An extension of the assessment period, as well as the opportunity to refute evidence, has been suggested as ways to support more informed and effective decision‐making by CITES Parties, whose composition of delegations varies greatly in their experience of marine species management and trade. Experts welcomed a greater coherence of advice between fishery and non‐fishery sources in the long term, and proposed a range of suggested improvements for the delivery of information and advice to CITES Parties.
... Sharks belong to the class Chondrichthyes and play a crucial role in marine ecosystems, acting as ecological stabilizers due to the evolutionary pressure they exert on their prey . Most shark species exhibit K-strategist characteristics, with a limited capacity for population recovery and are, therefore, naturally susceptible to overfishing (Dulvy et al. 2017;Ward-Paige et al. 2012). In fact, most shark populations are currently under serious threats, with close to a quarter of all species at risk for extinction . ...
Article
Shark catches have increased worldwide, threatening the survival of several species. This study describes historical trends concerning shark consumpƟon and commercializaƟon by arƟsanal fishers in northeastern Brazil. Semi‐structured quesƟonnaires were applied and respondents pointed out that sharks used to be locally regarded as low‐quality fish in the past and rejected by fish consumers, with low fisher consumpƟon frequency. However, this has changed in recent decades, as a total of 95.4% (n=62) of the quesƟonnaire respondents reported currently consuming shark meat, while 61.5% (n=40) highlighted its high quality. In addiƟon, most interviewees (90.8%; n=59) reported decreasing numbers of sharks caught over Ɵme, following worldwide trends, leading to decreased fisher access to shark meat. Because of this, most respondents (70.7%, n=46) now consider it more advantageous to sell the sharks they catch than to consume them. In addiƟon, the local commercializaƟon of these fish is currently based on immature coastal species (<1 m). Thus, economic and biological studies on local shark populaƟons are suggested in order to preserve local fisher culture and ensure food security for arƟsanal fisher communiƟes and a long‐term sustainable fishery and conservaƟon of exploited species.
... New conservation approaches are required to increase public engagement in marine policy in support of shark conservation (Friedrich et al., 2014). Education and public awareness campaigns can be effective tools used to drive policy actions and market demands in regard to elasmobranch conservation (Ward-Paige et al., 2012). ...
... As a result they require strong conservation management and an extended time to recover to their original status relative to many bony fish species. These traits can explain the decline of many shark populations in several parts of the world (Dulvy et al., 2008;Stevens et al., 2000;Ward-Paige et al., 2012). However, directed fishing or bycatch are not the only drivers of these declines, with other threats including, but not limited to, nearshore habitat degradation through destruction and contamination via human impacts and global climate change with its associated biogeochemical impacts (Lowry, 2017). ...
Chapter
Mexico is a country that makes heavy use of the shark populations that inhabit the southern portion of the Northeast Pacific Ocean (NEP). Shark meat has become an essential food source in this country, while shark fins are used to supply traditional Asian markets. In addition to consumptive utilization, charismatic shark species support an ecotourism industry that has gained significance in several tourist resorts across the country. In this concluding chapter, we recap the contents of chapters included in volumes 83 and 85 in the Advances in Marine Biology series. The chapters in these volumes address biodiversity, conservation genetics, trophic ecology, migratory movements, fisheries, and shark ecotourism, allowing us to understand the state of knowledge relevant to human: shark interactions in the Mexican Pacific. We discuss the challenges for the sustainable use and conservation of sharks in the southern NEP and highlight the need for a more holistic management approach that includes economic and social factors. To meet these challenges, we recommend updating the Mexican National Plan of Action for Sharks published in, 2004, such that it may continue serving as a roadmap for the conservation and management of sharks in the southern NEP during the years to come.
... Elasmobranch recovery is possible but requires in-situ management actions (Ward-Paige et al. 2012). Nursery protection has been proposed (Beck et al. 2001), as juvenile survival seems to be key for shark conservation (Cortés 2002). ...
Article
Full-text available
The blue shark Prionace glauca, among the most common and widely studied pelagic sharks, is a top predator, exhibiting the widest distribution range. However, little is known about its population structure and spatial dynamics. With an estimated removal of 10 to 20 million individuals per year by fisheries, the species is classified as “Near Threatened” by International Union for Conservation of Nature. We lack the knowledge to forecast the long-term consequences of such a huge removal on this top predator itself and on its trophic network. The genetic analysis of more than 200 samples collected at broad scale (from Mediterranean Sea, North Atlantic and Pacific Oceans) using mtDNA and nine microsatellite markers allowed to detect signatures of genetic bottlenecks but a nearly complete genetic homogeneity across the entire studied range. This apparent panmixia could be explained by a genetic lag-time effect illustrated by simulations of demographic changes that were not detectable through standard genetic analysis before a long transitional phase here introduced as the “population grey zone”. The results presented here can thus encompass distinct explanatory scenarios spanning from a single demographic population to several independent populations. This limitation prevents the genetic-based delineation of stocks and thus the ability to anticipate the consequences of severe depletions at all scales. More information is required for the conservation of population(s) and managements of stocks, which may be provided by large scale sampling not only of individuals worldwide, but also of loci genome-wide.
... As a result they require strong conservation management and an extended time to recover to their original status relative to many bony fish species. These traits can explain the decline of many shark populations in several parts of the world Ward-Paige et al., 2012). However, directed fishing or bycatch are not the only drivers of these declines, with other threats including, but not limited to, nearshore habitat degradation through destruction and contamination via human impacts and global climate change with its associated biogeochemical impacts (Lowry, 2017). ...
Book
This is the second book in a series about the sharks of Mexico their biology, ecology and conservation. These are books in Elsevier's Advances in Marine Biology Series vol 83 (part A) and 85 (part B). Topics covered are: Shark movement patterns in the Mexican Pacific: A conservation and management perspective; Fisheries interactions and the challenges for target and nontargeted take on shark conservation in the Mexican Pacific; Shark ecotourism in Mexico: Scientific research, conservation, and contribution to a Blue Economy; and Conclusions:Doweeatthemorwatchthem, orboth?Challenges for conservation of sharks in Mexico and the NEP
... MPAs are generally considered effective in protecting species with limited movements 33,34 , but recent evidence pointed out their potential to conserve mobile and long-lived predators, including elasmobranchs 25,35 . Several very large FPAs have been established worldwide and are being promoted as a tool for conservation and recovery of pelagic species (including elasmobranchs) 36,37 . The recent designation of large FPAs has greatly helped in achieving global protection targets 38 . ...
Article
Full-text available
Elasmobranchs are heavily impacted by fishing. Catch statistics are grossly underestimated due to missing data from various fishery sectors such as smallscale fisheries. Marine Protected Areas are proposed as a tool to protect elasmobranchs and counter their ongoing depletion. We assess elasmobranchs caught in 1,256 fishing operations with fixed nets carried out in partially protected areas within Marine Protected Areas and unprotected areas beyond Marine Protected Areas borders at 11 locations in 6 Mediterranean countries. Twenty-four elasmobranch species were recorded, more than onethird belonging to the IUCN threatened categories (Vulnerable, Endangered, or Critically Endangered). Catches per unit of effort of threatened and data deficient species were higher (with more immature individuals being caught) in partially protected areas than in unprotected areas. Our study suggests that despite partially protected areas having the potential to deliver ecological benefits for threatened elasmobranchs, poor small-scale fisheries management inside Marine Protected Areas could hinder them from achieving this important conservation objective.
... La principal amenaza para muchas de las poblaciones de tiburón está relacionada con una alta captura dirigida y mortalidad incidental por varias pesquerías en el mundo, resultado de la alta demanda de productos de tiburón como carne y aletas (Ward-Paige et al., 2012). Por esta razón, varios autores reconocen la urgencia de fortalecer su manejo pesquero, para evitar su extinción, promover la recuperación de sus poblaciones y alcanzar pesquerías sostenibles de tiburón (Dulvy et al., , 2017. ...
Thesis
Full-text available
Sharks are a group of species vulnerable to overfishing, as they generally have relatively slow growth, mature at advanced ages, have low numbers of young per litter, and low natural mortality. The systematic exploitation of sharks in the Gulf of California (GC) is occurring since 100 years ago. Just as GC is considered essential habitat for the diversity and assembly of shark species, residents and migrants. This gulf is one of the seven marine regions of the world where neritic and pelagic sharks are one of the most threatened. Therefore, knowing and characterizing the fishing areas where the most diversity and richness of shark species caught in the GC occurs can contribute to the strengthening of the legal instruments for its fishing management with a spatial character and the conservation of its habitat. The aim of this study is 1) to identify the priority sharks species and 2) potentially strategic regions for the conservation and sustainable management of the artisanal fisheries of the GC. Also, investigate the relationship of densities by species with physical-environmental conditions. These characteristics can determine the distribution and occurrence of sharks in the GC. Information contained in the official landings from 2007 to 2017 was used, which included the volume of catch by species, the price on the local market and catch sites. Based on three criteria that correspond to the vulnerability of the species due to fishing, their historical importance and economic value, the shark species that are considered priorities for their conservation and management of their fishery were selected. Twelve fishing regions are identifying as Fishing Operation Regions (ROP) using a Geographic Information System, the main ROPs of the priority species are identified. Through Generalized Additive Models (GAM), the relationship of the catch density of each species with the physical-environmental conditions, such as sea surface temperature, bathymetry, the slope between isobath and the type of substrate, was assessed between ROPs. The results shown that the priority species are A. pelagicus, C. falciformis, C. leucas, C. limbatus, I. oxyrinchus, M. henlei, N. velox, R. longurio, S. lewini, S. zygaena and S. californica. ROP 1 and 7, respectively south and north of the GC, present greater diversity since up to 10 of 11 priority shark species are catch there. The highest catch of these species occurs in ROP 1 and 12, south of the GC, so that they can be considered as the strategic ROPs for the conservation of shark species in the GC. Likewise, the GAM suggests that the physiography of the CG determines the distribution and occurrence of species with oceanic and coastal habits.
... Effective ocean conservation requires knowledge of the spatial ecology of marine species and the identification of essential habitats supporting their populations (Ward-Paige et al., 2012). We used non-destructive baited videography to begin the task of understanding patterns in the structure, richness, and abundance of pelagic communities across a vast, geodiverse seascape: the Oceanic Shoals AMP. ...
Article
Full-text available
The conservation of marine biodiversity is firmly embedded in national and international policy frameworks. However, the difficulties associated with conducting broad-scale surveys of oceanic environments restrict the evidence base available for applied management in pelagic waters. For example, the Oceanic Shoals Australian Marine Park (AMP) was established in 2012 in a part of Australia's continental shelf where unique topographic features are thought to support significant levels of biodiversity, yet where our understanding of ecological processes remains limited. We deployed mid-water baited remote underwater video systems (mid-water BRUVS) in the Oceanic Shoals AMP to provide the first non-extractive baseline assessment of pelagic wildlife communities in the area. We used these observations and high-resolution multibeam swaths of the seafloor to explore potential relationships between prominent geomorphological features and the (i) composition, (ii) richness, and (iii) relative abundance of pelagic communities. We documented 32 vertebrate species across three sampling areas, ranging from small baitfish to large sharks and rays, and estimated that up to nearly twice as many taxa may occur within the region as a whole. This highlights the Oceanic Shoals AMP as a reservoir of biodiversity comparable to other documented offshore oceanic hotspots. Our results also confirm the AMP as a possible distant foraging destination for IUCN red listed sea turtles, and a potential breeding and/or nursing ground for a number of charismatic cetaceans. Model outputs indicate that both species richness and abundance increase in proximity to raised geomorphic structures such as submerged banks and pinnacles, highlighting the influence of submarine topography on megafauna distribution. By providing a foundational understanding of spatial patterns in pelagic wildlife communities throughout a little studied region, our work demonstrates how a combination of non-destructive sampling techniques and predictive models can provide new opportunities to support decision-making under data shortage.
... La principal amenaza para muchas de las poblaciones de tiburón está relacionada con una alta captura dirigida y mortalidad incidental por varias pesquerías en el mundo, resultado de la alta demanda de productos de tiburón como carne y aletas (Ward-Paige et al., 2012). Por esta razón, varios autores reconocen la urgencia de fortalecer su manejo pesquero, para evitar su extinción, promover la recuperación de sus poblaciones y alcanzar pesquerías sostenibles de tiburón (Dulvy et al., , 2017. ...
... Measures to protect juveniles and nursery grounds, and to minimize fishing mortality on mature females might have tangible benefits for the stock (Apostolaki et al., 2006). Furthermore, several studies have shown that the survival of juveniles strongly influence the viability or recovery of elasmobranch populations (Brander, 1981;Ward-Paige et al., 2012;Elliott et al., 2020b). Since L. fullonica's core area of distribution is within an area of high fishing pressure (Sharples et al., 2013;ICES, 2018), any management measures that decreases mortality and/or increases recruitment, facilitating population maintenance or recovery (Polunin, 2002) should be investigated. ...
Article
Little is still known about the biology and ecology of many elasmobranchs which often inhibits species specific management measures from being implemented. The primary aim of this study was to improve the knowledge on the distribution and habitat use of the threatened and data deficient shagreen ray, Leucoraja fullonica, using fisheries dependent data. To model its distribution, we used Bayesian hierarchical modelling, taking into consideration imperfect capture from the non-random nature of fishing gear type and spatial autocorrelation. Our second objective was to identify the potential functional role of the high occurrence area by analysing spatial length segregation using a generalised additive mixed model. From five environmental variables, depth, distance to coast, and seabed sediment type were used to model its habitat. L. fullonica was found to mainly inhabit an area of high concentration between the southern Celtic Seas and the northern Bay of Biscay. Within this area, smaller individuals were found in the deeper south-western part and larger individuals in shallower waters, closer to the coast, suggesting ontogenetic shift or spawning migration. L. fullonica were mainly caught by bottom trawl fishing gears. The isolated habitat occupancy of this species may increase its vulnerability, particularly since high fishing pressure has been observed in this area. These results highlight the importance of fisheries-dependent data for data-poor species and provide valuable new information on its ecology when considering management or conservation measures at a species level.
... Cebrián-Piqueras et al., (2020 have shown that nature-related activities and education could play a crucial role in obtaining a deeper understanding of local natural environments. Positive public and stakeholder attitude towards sharks is important to guide decision-making, and conservation and management actions (Simpfendorfer et al., 2011;Ward-Paige et al., 2012), as communities tend to want to protect animals and environments that they are knowledgeable about (Giovos et al., 2021). ...
Article
Full-text available
The tendency of world media to villainize of sharks has likely contributed to a disparity in the distribution of research and conservation resources among threatened marine megavertebrates, with elasmobranchs losing out. Increased public knowledge on elasmobranchs can shape public attitude and foster and gain support for elasmobranch conservation. Through an online survey, this study aimed to evaluate the drivers of public knowledge and examine linkages between awareness of elasmobranchs and attitude toward their conservation. To explore the relationships and effects between the different predicting variables and public elasmobranch knowledge and attitude indices, bi-and multi-variate analysis and a partial least squares path model were used. The results indicated that the average public elasmobranch knowledge of the Cypriot population was moderate and the average public attitude towards elasmobranchs was relatively low. Marine-related activities and marine-related education were highly correlated with increased public elasmobranch knowledge and were the strongest predictors of the partial least squares path model which explained a high degree of variation in elasmobranch knowledge. Public elasmobranch knowledge was highly correlated with public attitude towards elasmobranchs. The findings of this study highlighted the importance of ocean literacy and education and provide insights into the mechanisms for developing and designing successful advocacy actions for elasmobranch conservation.
... Considering the current change in the fishing pattern in the Strait of Sicily, attention should be paid to limiting the impact of deep-water red shrimp fisheries on sensitive species such as Elasmobranchii living on slope fishing grounds off the southern coast. Together with more effective control of fishing efforts, management measures aimed at increasing the selectivity of trawling gear, by either implementing an ad hoc modified sorting grid [62,84], raising the footrope [85], or cutting the rigging twine [39]; increasing the number of cartilaginous fish returned to the sea alive through education on proper handling [86][87][88][89], and protecting areas and periods where spawning and juveniles aggregate would contribute to improving the state of Elasmobranchii populations that suffer the impact of fisheries [90,91]. ...
Article
Full-text available
Elasmobranchii (sharks and rays), which have peculiar and vulnerable life-history traits, are highly threatened by fishing activities. Indeed, between 53% and 71% of Mediterranean elasmobranch species are at risk of extinction. In this context, using the abundance MSY (AMSY) model, the present study provides an assessment of 20 batoids and 16 shark species in the Strait of Sicily, sampled during a bottom trawl survey from 1995 to 2020. Overall, the outputs underline a progressively improving condition for shark and ray assemblages of both shelf and eurybathic zones. As for slope-dwelling species, a horseshoe-shaped dynamic, characterized by a progressive decrease in relative harvesting pressure and an increase in relative biomass followed by an increase in fishing pressure and decrease in biomass, was detected. The dynamics of the Elasmobranchii living in the Strait of Sicily appear to be affected by changes in the fishing patterns of trawlers, showing a shift from shallow water to bathyal fishing grounds and targeting deep-water red shrimp. In this context, it seems wise to limit the impact of deep-water fisheries on Elasmobranchii by reducing fishing efforts and implementing ad hoc management measures aimed at safeguarding these vulnerable species.
... Although not the most imminent threat to chondrichthyans and only recognized as a threat in the frst decade of the 21st century, climate change has the potential to amplify the effects of fsheries and habitat degradation (Dulvy et al. 2014;Vedor et al. 2021;Ward-Paige et al. 2012). Moreover, the effcacy of conservation measures may also be undermined under climate change. ...
... It is also important for the maintenance of healthy marine ecosystems that could provide services to human society 84 . Accordingly, management focus will need to include localized protection measures, such as local seasonal closures or marine reserves to properly match the geographic scale of the population 85 . Specifically, for the east coast of Australia, we recommend to further investigate our findings, to elucidate the current abundance and distribution of the two populations and establish measures to protect the putative southern population component, which appears to have faced a significant historical decline, primarily driven by either direct and indirect exploitation. ...
Article
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Over the last century, many shark populations have declined, primarily due to overexploitation in commercial, artisanal and recreational fisheries. In addition, in some locations the use of shark control programs also has had an impact on shark numbers. Still, there is a general perception that populations of large ocean predators cover wide areas and therefore their diversity is less susceptible to local anthropogenic disturbance. Here we report on temporal genomic analyses of tiger shark (Galeocerdo cuvier) DNA samples that were collected from eastern Australia over the past century. Using Single Nucleotide Polymorphism (SNP) loci, we documented a significant change in genetic composition of tiger sharks born between ~1939 and 2015. The change was most likely due to a shift over time in the relative contribution of two well-differentiated, but hitherto cryptic populations. Our data strongly indicate a dramatic shift in the relative contribution of these two populations to the overall tiger shark abundance on the east coast of Australia, possibly associated with differences in direct or indirect exploitation rates.
... Science-based management, well-enforced MPAs, and protection of aggregation sites and critical habitats (e.g., nursery areas) are each considered important to ensure the recovery of elasmobranch populations [80]. The adoption of each of these components in a holistic approach to manta ray conservation and management by Raja Ampat government agencies has allowed manta populations in the archipelago to thrive. ...
Article
Despite a precipitous decline in global populations of sharks and rays over the past fifty years due to overfishing, and increasing concerns over the conservation status of manta and devil rays worldwide, manta ray populations in Raja Ampat in the Papuan Bird’s Head Seascape of Indonesia are seemingly thriving. Reef manta rays (Mobula alfredi) in particular are abundant and have higher rates of pregnancy than have been recorded elsewhere in the Indo-Pacific, and have demonstrated a significant population increase over the past decade of monitoring. Here we document two decades’ of conservation efforts in the Bird’s Head Seascape (BHS) which, when considered in their entirety, represent an organically-developed, holistic approach to manta ray conservation that has demonstrated compelling evidence of success despite ongoing challenges. We provide detailed insights on the adaptive, continuously evolving approach used for manta ray conservation in the BHS in order that this approach might inform similar efforts towards elasmobranch conservation in other areas of the developing tropics.
... climate change effects, overfishing, bycatch and their relative downstream threats;Ferretti et al., 2005;Elliott et al., 2020). To date, mitigation measures, such as the designation of marine protected areas or shark sanctuaries and fishing effort changes, have been adopted at different geographical scales to help allow the recovery and/or protection of local populations of vulnerable species(Baum et al., 2003;Shephard et al., 2012;Ward- Paige et al., 2012). Nevertheless, the establishment and effectiveness of such actions may depend on different factors, as population dynamics or mating success may not represent a possible solution. ...
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1. The Mediterranean starry ray (Raja asterias) populations within the Mediterranean Sea are susceptible to high rates of bycatch in the multispecies trawl fisheries. Understanding its population structure and identifying critical habitats are crucial for assessing species vulnerability and setting the groundwork for specific management measures to prevent population decline. 2. To assess the population structure of R. asterias in the Mediterranean, the genetic variation in nine population samples at one mitochondrial marker and eight nuclear microsatellite loci was analysed. Moreover, 172 egg cases collected in the Strait of Sicily were identified at species level using integrated molecular and morphological approaches. 3. Genetic analyses revealed that the Mediterranean starry ray comprises three distinct units inhabiting the western, the central-western, and the central-eastern areas of the Mediterranean. An admixture zone occurs in the Strait of Sicily and the Ionian Sea, where individuals of the central-western and central-eastern population units intermingle. 4. The joint morphometric-genetic analyses of rajid egg cases confirmed the presence of more than one species in the admixture area, with a predominance of egg cases laid by R. asterias. DNA barcoding revealed that egg cases and embryos of R. asterias shared several haplotypes with adult individuals from the central-western and central-eastern Mediterranean Sea, revealing that females of both populations laid numerous eggs in this area. 5. According to these findings, detailed taxonomic determination of egg cases, when combined with seasonal migration studies, could improve the capability to identify important spawning or nursery areas for the Mediterranean starry ray, particularly in those admixture zones relevant to maintaining genetic diversity. 6. Finally, these new insights should be considered to update the Action Plan for the Conservation of Cartilaginous Fishes in the Mediterranean Sea with effective measures to reduce the impact of skate bycatch in trawling and safeguard egg cases in nursery areas.
... Moreover, Davidson et al. (2016) found that declines in shark catches are correlated with large coastal human populations, large shark export volumes, high endemic diversity, and small continental shelves. Despite initiatives to reverse declining trends, only a quarter of the documented recoveries were a consequence of improved management, while the remaining 75% were a consequence of predatory or competitive releases (Ward-Paige et al., 2012;Davidson et al., 2016). ...
Article
The impact of shrimp trawl fisheries on slow-growing demersal sharks, skates and rays has been widely documented. Yet, a lack of catch records and biological information has hindered improvements in elasmobranch bycatch management, particularly in tropical regions. When information is scarce, data-poor methods can be valuable tools to guide the management and conservation of vulnerable marine taxa. Here we combined an Ecological Risk Assessment commonly used in data-deficient fisheries (Productivity Susceptibility Analysis or PSA) with a spatial analysis (Hotspot Analysis) to (i) identify which elasmobranch species are most vulnerable to the Costa Rican shrimp trawl fishery, and (ii) locate areas and seasons with high concentrations of vulnerable elasmobranchs. According to the results of our PSA, the scalloped hammerhead (Sphyrna lewini), prickly shark (Echinorhinus cookei), and long-tail stingray (Hypanus longus) were the most vulnerable species, while the least vulnerable species were small batoids of the Urotrygonidae family. We identified large information gaps, namely demographic parameter estimates and long-term bycatch trends. Spatial aggregations of vulnerable elasmo-branchs occurred near highly productive estuaries and coastal habitats, especially at depths of 50-100 m. Based on our findings, PSA and Hotspot analyses can be powerful tools to identify spatial areas where trawl fishing grounds overlap with the habitat of vulnerable bycatch species, and thus can be used to design spatial trawling closures that protect species at risk. We therefore conclude that our methodological approach may aid in the implementation of ecosystem-based fisheries management in data-poor situations.
... Following international concern over rapidly dwindling shark populations, several mitigation measures are advocated by biologists and conservationists. Spatial closures, such as marine protected areas (MPAs) and no take marine reserves as well as fishing bans are some of the fisheries management strategies that have been implemented to slow and reverse the effect of large-scale overfishing on shark populations (Ward-Paige et al., 2012). However, implementation of these measures has the potential to adversely impact regions with significant shark fisheries and stakeholders who directly depend on shark and other marine resources for their livelihoods. ...
Article
Small-scale shark fisheries support the livelihoods of a large number of coastal communities in developing countries. Shark meat comprises a cheap source of protein and is traded locally in many parts in developing countries, while the skins, oil, and fins are exported to the international market. This study addresses a gap in literature regarding the importance of elasmobranchs to key shark-fishing communities and the degree to which trade in shark products (meat and fins) vary in time and among fishing communities in Ghana. We interviewed 85 fishers and traders involved in shark fisheries in Axim, Dixcove, and Shama communities using semi-structured questionnaires. Fishing was the primary source of income and accounted for 58.5% of the total household income of respondents. Other important economic activities were fish processing (16.0%), fish retailing (13.3%), and small businesses (2.5%). One-third and often two-thirds of respondents generated between 80% and 100% of their income from shark fisheries: Axim (65%), Dixcove (68%), and Shama (35%). Shark meat consumption was common among fishers and traders and represents a substantial source of protein in the diet of the study communities. Hammerhead sharks (Sphyrna spp) and Bull Shark (Carcharhinus leucas) have the most valuable fins and meat. Further, 75% and 95% of fishers and traders, respectively, see fishing and trading of shark meat as their last safety-net and, therefore, tend to be satisfied with their jobs. Non-fishing related livelihood streams including small businesses and transportation were the major fallback activities both fishers and traders preferred to rely on if there is a ban on the exploitation of sharks in Ghana. Overexploitation of these species will compromise food ecosystem functionality and security. Thus, any shark management strategy needs to urgently restraint mortality to sustainable levels, which, in the short-term, must take into consideration the preferred livelihood fallback options outlined by fishers and traders, and implement them to ensure the long-term benefits of the intervention.
... Retention of incidentally caught elasmobranchs is on the rise for a variety of reasons, with little management oversight (Oliver et al. 2015, James et al. 2016. New markets and demand can drive the retention of incidental elasmobranch catches (Walker 1998, Fong & Anderson 2002 as traditional target species decline (Ward-Paige et al. 2012, Dulvy et al. 2014, resulting in unregulated removals of elasmobranchs (Davies et al. 2009, James et al. 2016). Nontargeted and unmanaged catch can negatively affect elasmobranch populations if mortality for these species goes undocumented and is above maximum sustainable yield (Oliver et al. 2015). ...
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Effective management of multispecies fisheries in large marine ecosystems is challenging. To deal with these challenges, fisheries managers are moving toward ecosystem-based fishery management (EBFM). Despite this shift, many species remain outside protective legislation or fishery management plans. How do species that fall outside of formal management structures respond to changes in fisheries management strategies? In 2011, the US West Coast Groundfish Fishery (WCGF) shifted management to an Individual Fishing Quota (IFQ) program. We used data collected by fisheries observers to examine the impact of this shift on elasmobranch catch (sharks, skates, rays). Historically, not all elasmobranchs were included in the WCGF Management Plan, making them vulnerable to fishing mortality. We grouped elasmobranchs into 8 groups based on 14 ecomorphotypes to examine relative catch within groundfish fishing sectors during the period 2002-2014. Of the 22 sharks and 18 skates and rays that these fisheries capture, 9 are listed as Near Threatened or greater on the IUCN Red List and 10 species are listed as Data Deficient by IUCN. The bycatch of 4 non-managed elasmobranch species was reduced under the IFQ program; IFQ management had no significant impact on the remaining 27 species caught by the IFQ fleet. Overall, catch of non-managed elasmobranchs was relatively low. We show that groups of ecomorphotypes co-occur within fisheries, suggesting natural management units for use in EBFM. This work helps identify gaps in monitoring and assessing the impact of management and policy on elasmobranch populations.
... Existen ejemplos de varias poblaciones de elasmobranquios que han estabilizado o comenzado a recuperar su abundancia como resultado de la aplicación de medidas de manejo tradicionales que incluyen cuotas, capturas máximas permisibles, restricciones de tallas, límites de esfuerzo, restricciones de redes y áreas de veda temporales (Ward-Paige et al., 2012). Por lo tanto, la implementación de medidas de manejo como la analizada en este estudio es importante para proteger dichas especies y lograr una explotación sustentable. ...
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In 2007 the Comisión Técnica Mixta del Frente Marítimo established a closed area to bottom trawl in fishing rectangle 3656 to protect chondrichthyan reproductive aggregations and juveniles. The aim of this work was to analyze the evolution of said measure, the skate and shark landings declared during the 2006-2014 period in said rectangle and the distribution of the fleet before and after implementation. In the period evaluated, the duration of the closed area it was extended from 59 to 151 days and a reduction of tonnes of skates and sharks declared in the Argentine Uruguayan Common Fishing Zone of rectangle 3656 and an increase in the participation of said species in landings of the area of provincial jurisdiction was observed. The same trend was proved in the fishing activity if compare the season 2006-2007 (without closed area) and the season 2012-2013 (with closed area). During the closed season a northeast displacement of activities, a high catch level and fishing operations in the adjacent rectangles were observed.
... Generally, spatial management is carried out through the implementation of xed marine protected areas (MPA), but it can also be implemented by seasonal12 or dynamic13 spatial closures. MPAs are increasingly becoming popular tools to limit the extraction of sensitive sh species and buffer the effects of sheries in surrounding marine ecosystems14 , 15. While there is substantial evidence supporting the implementation of MPAs in maintaining the biomass and diversity of coastal sh species16 , 17, their potential to protect highly mobile species is still the subject of debate18-20. ...
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Spatial management through the implementation of marine protected areas is one strategy to limit the extraction of sensitive marine species. Understanding the area used by marine life is thus a key step towards the evaluation of the management framework and efficacy of a protected area. To provide information of the protective coverage of the Galapagos Marine Reserve (GMR), we assessed the habitat utilization distribution (UD) of hammerhead and blacktip sharks in the GMR. Fifteen hammerhead sharks and 27 blacktip sharks were tagged with SPOT and SPLASH satellite tags in the north and south-central regions of the GMR between 2007 and 2012. Our results show nearly 90% of hammerhead shark’s UD was enclosed by the reserve boundary during the cold season (June-October), yet this decreased to only ~30% with the advent of the warm season (December-April). Conversely, blacktip sharks’ UD was 100% enclosed by the reserve boundaries in all seasons. Season and depth were the most important environmental parameters defining the UD of hammerhead sharks; whilst year and eddy kinetic energy were the most important parameters for blacktip sharks. These findings suggest the size of the GMR may be effective for blacktip sharks but seasonally effective for hammerhead sharks.
... Consequently, this species gained more attention concerning their protection and conservation (Young and Carlson 2020). Many programs are being initiated to recover and protect endangered sharks through sustainable management plans (Ward-Paige et al. 2012). Even though shark finning and export of fins have been banned in India, the fishery of oceanic whitetip sharks is still not restricted. ...
Article
Sharks are undergoing population declines worldwide and it is imperative to devise conservation and management strategies to prevent their extinction. Oceanic whitetip sharks are large pelagic sharks distributed circumglobally and recent IUCN assessments classified them as “critically endangered.” Considering their vulnerability, we investigated the intraspecific diversity and genetic stock structure of oceanic whitetip shark, Carcharhinus longimanus, along the Indian coast using mitochondrial control region sequences so that viable management guidelines can be formulated in the Indian Ocean region. Population genetic analyses revealed a lack of significant genetic differentiation along the Indian coast indicating substantial gene flow and connectivity among populations. Comparisons of data of the present study with that of Atlantic Ocean regions indicated significant connectivity and gene flow between Indian and East Atlantic regions and a lack of connectivity between Indian and West Atlantic Ocean regions. Oceanic whitetip sharks have substantial capacity for oceanic migration resulting in the mixing of gene pools. Despite these capabilities, overfishing is one of the major drivers of population decline worldwide, resulting in severe fragmentation of populations. Based on the results of the present study, this species can be managed as a single stock along the Indian coast. Further co-management measures along with countries bordering East Atlantic coast can also be devised. Management should consider a complete or seasonal ban of the fishery in addition to restrictions in gear types.
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Over the last century, many populations of sharks have been reduced in numbers by overexploitation or attempts to mitigate human-shark interactions. Still, there is a general perception that populations of large ocean predators cover wide areas and therefore their diversity is less susceptible to local anthropogenic disturbance. Here we report retrospective genomic analyses of DNA using archived and contemporary samples of tiger shark ( Galeocerdo cuvier ) from eastern Australia. Using SNP loci, we documented a significant overall change in genetic composition of tiger sharks born over the last century. The change was most likely due to a shift over time in the relative contribution of two well differentiated, but hitherto cryptic populations. Our data strongly indicate a dramatic shift in relative contribution of the two populations to the overall tiger shark abundance of the east coast of Australia, possibly associated with differences in direct or indirect exploitation rates.
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Quantifying the drivers of population size in reef sharks is critical for the development of appropriate conservation strategies. In north-west Australia, shark populations inhabit coral reefs that border growing centres of human population, industry, and tourism. However, we lack baseline data on reef sharks at large spatial scales (hundreds of km) that might enable managers to assess the status of shark populations in the face of future development in this region. Here, we examined the occurrence, abundance and behaviour of apex (Galeocerdo cuvier, Carcharhinus plumbeus) and reef (C. amblyrhynchos, C. melanopterus, Triaenodon obesus) sharks using > 1200 deployments of baited remote underwater stereo-video systems (stereo-BRUVs) across > 500 km of coastline. We found evidence for species-specific influences of habitat and fishing activities on the occurrence (probability of observation), abundance (MaxN) and behaviour of sharks (time of arrival to the stereo-BRUVs and likelihood of feeding). Although the presence of management zoning (No-take areas) made little difference to most species, C. amblyrhynchos were more common further from boat ramps (a proxy of recreational fishing pressure). Time of arrival for all species was also influenced by distance to boat ramp, although patterns varied among species. Our results demonstrate the capacity for behavioural metrics to complement existing measures of occurrence and abundance in assessing the potential impact of human activities on shark populations.
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The Caribbean reef shark (Carcharhinus perezi) is an economically important species in The Bahamas, where it is protected from fishing and is a mainstay for the shark dive tourism industry. Significant declines in abundance are suspected throughout much of its range, making the study of its life history and spatial ecology important for effective fisheries management and conservation planning. We used tag-recapture data collected in The Bahamas between 2008 and 2020 to investigate the species’ linear movements, population characteristics, life history, and growth. Sharks moved little between tag and recapture events (range: 0 to 8 km) despite multiple years at liberty for many sharks (range: 2 days to 7.1 years). We found no evidence of seasonal migration. We used a combined-sex von Bertalanffy growth function to estimate an asymptotic mean length at age (TL∞) of 205.8 cm total length and a growth coefficient (k) of 0.06. Theoretical maximum longevity was 43.3 to 57.8 years. Median male length at maturity (L50) was 148.9 cm total length (95% CI: 146.1–151.5 cm), which likely occurs around 14.8 years of age. Our results indicate slower growth of the Caribbean reef shark in The Bahamas than previously estimated in Venezuela. Our results suggest the Caribbean reef shark may be more vulnerable to overfishing and extirpation at the northern extent of its range than previously considered and that large no-take areas may be an effective conservation tool for this species.
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Climate change is affecting thermal regimes globally, and organisms relying on their environment to regulate biological processes face unknown consequences. In ectotherms, temperature affects development rates, body condition, and performance. Embryonic stages may be the most vulnerable life history stages, especially for oviparous species already living at the warm edge of their distribution, as embryos cannot relocate during this developmental window. We reared 27 epaulette shark (Hemiscyllium ocellatum) embryos under average summer conditions (27 °C) or temperatures predicted for the middle and end of the twenty-first century with climate change (i.e., 29 and 31 °C) and tracked growth, development, and metabolic costs both in ovo and upon hatch. Rearing sharks at 31 °C impacted embryonic growth, yolk consumption, and metabolic rates. Upon hatch, 31 °C-reared sharks weighed significantly less than their 27 °C-reared counterparts and exhibited reduced metabolic performance. Many important growth and development traits in this species may peak after 27 °C and start to become negatively impacted nearing 31 °C. We hypothesize that 31 °C approximates the pejus temperature (i.e., temperatures at which performance of a trait begin to decline) for this species, which is alarming, given that this temperature range is well within ocean warming scenarios predicted for this species’ distribution over the next century.
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Bentfin devil ray (Mobula thurstoni) was recorded for the first time in Morotai waters on 3rd March 2017. In a conservation management context, it is important to clarify the population of Mobula thurstoni and their relations with their habitat. Thus, we examined the existence of Mobula thurstoni with the physical parameters: depth, temperature, visibility, current, weather, and tidal. We measured the existence of Mobula thurstoni with the Underwater Visual Census (UVC) combined with Diver Operated Video (DOV) census. The research from 3rd March to 14th July 2017 (50 dives) showed the Frequency of Occurence (FO) is 50% per single dive. The highest aggregation of 30 Mobula thurstoni was recorded at 14th May 2017 and the average sighting was 3.1 Mobula thurstoni per single dive. Among the examined parameters, it was found that strong factor affecting the sighting of Mobula thurstoni were at the depth of 30-35 m, temperature of 30°C, visibility of 16-20 m, low current (< 1 knot), sunny weather, and tidal category of B. Analysis of UVC and DOV results show that the research location was categorised as feeding location for the Mobula thurstoni.
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Long-lived marine megavertebrates (e.g. sharks, turtles, mammals, and seabirds) are inherently vulnerable to anthropogenic mortality. Although some mathematical models have been applied successfully to manage these animals, more detailed treatments are often needed to assess potential drivers of population dynamics. In particular, factors such as age-structure, density-dependent feedbacks on reproduction, and demographic stochasticity are important for understanding population trends, but are often difficult to assess. Lemon sharks ( Negaprion brevirostris ) have a pelagic adult phase that makes them logistically difficult to study. However, juveniles use coastal nursery areas where their densities can be high. Thus, we use a stage-structured, Markov-chain stochastic model to describe lemon shark population dynamics from a 17-year longitudinal dataset at a coastal nursery area at Bimini, Bahamas. We found that the interaction between delayed breeding and demographic stochasticity accounts for 33 to 49% of the variance. Demographic stochasticity contributed all random effects in this model, suggesting that the existence of unmodeled environmental factors may be driving the majority of interannual population fluctuations. In addition, we are able to use our model to estimate the natural mortality rate of older age classes of lemon sharks that are difficult to study. Further, we use our model to examine what effect the length of a time series plays on deciphering ecological patterns. We find that — even with a relatively long time series — our sampling still misses important rare events. Our approach can be used more broadly to infer population dynamics of other large vertebrates in which age structure and demographic stochasticity are important.
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Sharks and their relatives (Elasmobranchii) are highly threatened with extinction due to various anthropogenic pressures. The abundant fossil record of fossil taxa has allowed the tracing of the evolutionary history of modern elasmobranchs to at least 250 MYA; nonetheless, exactly how far back the fossil record of living taxa goes has never been collectively surveyed. In this study, the authors assess the representation and extent of the fossil record of elasmobranchs currently living in our oceans by collecting their oldest records and quantifying first appearance dates at different taxonomic levels (i.e., orders, families, genera and species), ecological traits (e.g., body size, habitat and feeding mechanism) and extinction risks (i.e., threatened, not threatened and data deficient). The results of this study confirm the robust representation of higher taxonomic ranks, with all orders, most of the families and over half of the extant genera having a fossil record. Further, they reveal that 10% of the current global species diversity is represented in the geological past. Sharks are better represented and extend deeper in time than rays and skates. While the fossil record of extant genera (e.g., the six gill sharks, Hexanchus) goes as far back as c. 190 MYA, the fossil record of extant species (e.g., the sand shark, Carcharias taurus Rafinesque1810) extends c. 66 MYA. Although no significant differences were found in the extent of the fossil record between ecological traits, it was found that the currently threatened species have a significantly older fossil record than the not threatened species. This study demonstrate that the fossil record of extant elasmobranchs extends deep into the geologic time, especially in the case of threatened sharks. As such, the elasmobranch geological history has great potential to advance the understanding of how species currently facing extinction have responded to different stressors in the past, thereby providing a deep-time perspective to conservation.
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Length–weightrelationships (LWRs) of three species of pelagic sharks belonging to the family Carcharhinidae viz., the silky shark Carcharhinus falciformis and the graceful shark C. amblyrhynchoides and Alopidae viz, the pelagic thresher Alopias pelagicus, were estimated based on 525 samples collected from the longline and gillnet fishery of southeastern Arabian Sea from January 2016 to November 2018. Two major fish landing centres of Kerala, southwest coast of India were selected for sampling; Cochin (Lat. 09 ∘ 56 ′ 327 ′′ N, Long. 76 ∘ 15 ′ 764 ′′ E) and Munambam (Lat. 10 ∘ 10 ′ 965 ′′ N, Long. 76 ∘ 10 ′ 258 ′′ E). The estimated allometric coefficient b value ranged from 2.687 (A. pelagicus, N = 122) to 3.11 (C. falciformis, N = 295). Coefficient of determination scores ranged from 0.901 (A. pelagicus) to 0.984 (C. amblyrhynchoides, N = 108), indicating robustness of the samples analysed. Maximum total length presented for C. amblyrhynchoides in this study was a new record. The study reports first estimates of length–weight relationships for three important species of pelagic sharks which contribute to most of the shark catches in the region, and the generated parameters will be useful for the assessment of stocks and sustainable management of pelagic sharks in southeastern Arabian Sea.
Technical Report
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Basking sharks (Canadian Pacific population) are now suggested for listing as Endangered under the Species at Risk Act. We assessed recovery potential for basking sharks in Canadian Pacific waters by considering current status, potential sources of human-induced mortality, and various strategies to mitigate harm and promote recovery. We used a simulation model to evaluate scenarios that span the range of plausible human activities that cause mortality. Basking sharks in Canadian Pacific waters are considered to be part of a North American Pacific coast population which migrates into Canadian waters in spring and summer and winters off California. We therefore assess scenarios for the whole Pacific coast. Best estimates of current abundance range from 321 to 535 individuals. It is estimated that the decline from pre-exploited numbers exceeds 90%. It is believed that the bycatch of basking sharks in commercial fisheries limits current abundance. Other threats to the population (collisions with marine traffic, coastal development, ecotourism, etc) were identified, and mitigation proposals examined. Specified recovery objectives that could be assessed through simulation modelling include a) rebuild to 1000 breeding pairs; b) attain 30, 40, 50, and 99% of carrying capacity (assumed equal to pre-exploitation numbers), and c) attain 30, 40, 50,and 99% of initial biomass (assumed to be biomass prior to exploitation). Recovery potential was estimated as the number of years required to attain the recovery objectives under four levels of human-induced mortality and evaluated using two plausible catch histories. Using the best estimates of current abundance and stock decline, production model projections suggest that if a breeding population currently exists in the northeast Pacific Ocean, and no further human-induced mortality and changes to existing habitat occurs, that approximately 200 years are needed before population numbers will return to their unexploited states (Appendix C). If these animals are afforded complete protection, it will still take hundreds of years for the population to recover to 1000 breeding pairs. Recovery to 30% of the original biomass could happen within 45 years, if complete protection is afforded. The fishing mortality that the population can sustain without suffering further decline from the 2007 population ranges from 10 to 17 individuals annually coast wide including Canadian and US waters. Basking shark is a long lived species with a low rate of increase (i.e., Generation time of 22-33 years). The uncertainties in the projections of this report increases with time. To make progress in rehabilitating the basking shark population, will require government agencies to promote research and management activities for decades.
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Human values, perceptions, attitudes and interactions with the natural environment have been found to change over time, with social and economic information used to inform management decisions and actions. Content analysis is applied here to a 53-year long collection of the popular dive magazine, SportDiving, to identify recreational divers' experiences with regard to sharks and rays, the Great Barrier Reef (GBR) and marine protected areas (MPAs). This analysis suggests there has been a diversification of diver activities with the emergence of passive-observational activities such as SCUBA diving. Attitudes towards sharks and rays have changed significantly, with recreational divers changing from a group that could be described as adventure-seeking hunters to a group that can be described as nature-appreciating observers, suggesting an increase in conservation awareness. The GBR continues to be a highly regarded dive destination, with divers perceiving positive effects of protection within MPAs. However, declines in the abundance of large fish and sharks and rays were occasionally reported throughout the 53 year period. Collectively, these types of data can show changes in resource-use patterns, perceptions and attitudes and provide information that supplements scientific monitoring data. These data may be valuable where scientific data is scarce, historical records difficult to obtain, and where attitudinal change can significantly affect future resource use.
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1. Fishing spans all oceans and the impact on ocean predators such as sharks and rays is largely unknown. A lack of data and complicated jurisdictional issues present particular challenges for assessing and conserving high seas biodiversity. It is clear, however, that pelagic sharks and rays of the open ocean are subject to high and often unrestricted levels of mortality from bycatch and targeted fisheries for their meat and valuable fins. 2. These species exhibit a wide range of life-history characteristics, but many have relatively low productivity and consequently relatively high intrinsic vulnerability to over-exploitation. The IUCN}World Conservation Union Red List criteria were used to assess the global status of 21 oceanic pelagic shark and ray species. 3. Three-quarters (16) of these species are classified as Threatened or Near Threatened. Eleven species are globally threatened with higher risk of extinction: the giant devilray is Endangered, ten sharks are Vulnerable and a further five species are Near Threatened. Threat status depends on the interaction between the demographic resilience of the species and intensity of fisheries exploitation. 4. Most threatened species, like the shortfin mako shark, have low population increase rates and suffer high fishing mortality throughout their range. Species with a lower risk of extinction have either fast, resilient life histories (e.g. pelagic stingray) or are species with slow, less resilient life histories but subject to fisheries management (e.g. salmon shark). 5. Recommendations, including implementing and enforcing finning bans and catch limits, are made to guide effective conservation and management of these sharks and rays.
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A virgin population of porbeagles Lamna nasus in the northwest Atlantic Ocean supported annual catches of up to 9,000 metric tons (mt) in the early 1960s before the fishery collapsed in 1967. Low and apparently sustainable catches of about 350 mt in the 1970s and 1980s allowed the stock to partially rebuild before a new fishery arose in the early 1990s. The response of the population to this renewed fishing pressure has been unclear until now. However, a new population dynamics analysis suggests that population abundance has once again declined. On the basis of more than 140,000 length measurements, an extensive catch rate index, a confirmed growth model, and a catch-at-age matrix, it appears that at least 90% of the sexually mature population has been lost as fishing mortality has increased. Independent measures of fishing mortality ( F) based on Petersen analysis of tag-recaptures, Paloheimo Zs, and a population model all suggest that fishing mortality was about 0.20 in 2000. Biological reference points based on life table analysis indicate that fishing at F0.1 5 0.18 will result in population collapse, that F 5 0.08 corresponds to zero population growth, and that fishing mortality at maximum sustainable yield is about 0.04. Porbeagles have a low pup production rate and mature considerably after the age at which they first appear in the fishery. In light of the very low numbers of mature females now found in the population, it is unlikely that even the strict quota management now in place will allow the population to rebuild quickly. However, the shark fishing industry has actively supported scientific research and conservation practices in recent years, suggesting that long-term sustain- ability may still be possible.
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The impact of fishing on chondrichthyan stocks around the world is currently the focus of considerable international concern. Most chondrichthyan populations are of low productivity relative to teleost fishes, a consequence of their different life-history strategies. This is reflected in the poor record of sustainability of target shark fisheries. Most sharks and some batoids are predators at, or near, the top of marine food webs. The effects of fishing are examined at the single-species level and through trophic interactions. We summarize the status of chondrichthyan fisheries from around the world. Some 50% of the estimated global catch of chondrichthyans is taken as by-catch, does not appear in official fishery statistics, and is almost totally unmanaged. When taken as by-catch, they are often subjected to high fishing mortality directed at teleost target species. Consequently, some skates, sawfish, and deep-water dogfish have been virtually extirpated From large regions. Some chondrichthyans are more resilient to fishing and we examine predictions on the vulnerability of different species based on their life-history and population parameters. At the species level, fishing may alter size structure and population parameters in response to changes in species abundance. We review the evidence for such density-dependent change. Fishing can affect trophic interactions and we examine cases of apparent species replacement and shifts in community composition. Sharks and rays learn to associate trawlers with food and feeding on discards may increase their populations. Using ECOSIM, we make some predictions about the long-term response of ecosystems to fishing on sharks. Three different environments are analysed: a tropical shelf ecosystem in Venezuela, a Hawaiian coral reef ecosystem, and a North Pacific oceanic ecosystem. (C) 2000 International Council for the Exploration of the Sea.
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Growing concern for the world’s shark and ray populations is driving the need for greater research to inform conservation management. A change in public perception, from one that we need to protect humans from sharks to one where we must protect sharks from humans, has added to calls for better management. The present paper examines the growing need for research for conservation management of sharks and rays by synthesising information presented in this Special Issue from the 2010 Sharks International Conference and by identifying future research needs, including topics such as taxonomy, life history, population status, spatial ecology, environmental effects, ecosystem role and human impacts. However, this biological and ecological research agenda will not be sufficient to fully secure conservation management. There is also a need for research to inform social and economic sustainability. Effective conservation management will be achieved by setting clear priorities for research with the aid of stakeholders, implementing well designed research projects, building the capacity for research, and clearly communicating the results to stakeholders. If this can be achieved, it will assure a future for this iconic group, the ecosystems in which they occur and the human communities that rely on them.
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Humans can impact coral reef fishes directly by fishing, or indirectly through anthropogenic degradation of habitat. Uncertainty about the relative importance of those can make it difficult to develop and build consensus for appropriate remedial management. Relationships between fish assemblages and human population density were assessed using data from 18 locations widely spread throughout the Main Hawaiian Islands (MHI) to evaluate the significance of fishing as a factor potentially driving fish trends on a regional scale. Fish biomass in several groups was negatively correlated with local human population density and a number of lines of evidence indicate that fishing was the prime driver of those trends. First, declines were consistently evident among fish groups targeted by fishers, but not among lightly fished or non-target groupings, which indicates that declines in target groups were not simply indicative of a general decline in habitat quality along human population gradients. Second, proximity to high hum