ArticleLiterature Review

Recovery potential and conservation options for elasmobranchs

Wiley
Journal of Fish Biology
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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... Their low reproductive rates, slow growth, and mainly the impact of illegal, unreported, and unregulated fishing exacerbate their vulnerability (Baum et al., 2003;Bornatowski et al., 2014;Kotas et al., 2023;Pacoureau et al., 2021;Worm et al., 2013). To counter this decline, establishing marine-protected areas (MPA) and shark sanctuaries is crucial for restoring their natural habitats (Ward-Paige et al., 2012;Ward-Paige & Worm, 2017), but greater efforts need to be effective to implement sustainable fisheries management practices, including those in international waters (Murray et al., 2023;Salinasde-León et al., 2024). Additionally, shark tourism plays a significant role in conservation efforts, contributing positively to the economy through activities like diving (Cisneros-Montemayor et al., 2013;Gallagher & Hammerschlag, 2011;Vianna et al., 2011;Vianna et al., 2012;Ward-Paige & Worm, 2017). ...
... Their low reproductive rates, slow growth, and mainly the impact of illegal, unreported, and unregulated fishing exacerbate their vulnerability (Baum et al., 2003;Bornatowski et al., 2014;Kotas et al., 2023;Pacoureau et al., 2021;Worm et al., 2013). To counter this decline, establishing marine-protected areas (MPA) and shark sanctuaries is crucial for restoring their natural habitats (Ward-Paige et al., 2012;Ward-Paige & Worm, 2017), but greater efforts need to be effective to implement sustainable fisheries management practices, including those in international waters (Murray et al., 2023;Salinasde-León et al., 2024). Additionally, shark tourism plays a significant role in conservation efforts, contributing positively to the economy through activities like diving (Cisneros-Montemayor et al., 2013;Gallagher & Hammerschlag, 2011;Vianna et al., 2011;Vianna et al., 2012;Ward-Paige & Worm, 2017). ...
... To counter this decline, establishing marine-protected areas (MPA) and shark sanctuaries is crucial for restoring their natural habitats (Ward-Paige et al., 2012;Ward-Paige & Worm, 2017), but greater efforts need to be effective to implement sustainable fisheries management practices, including those in international waters (Murray et al., 2023;Salinasde-León et al., 2024). Additionally, shark tourism plays a significant role in conservation efforts, contributing positively to the economy through activities like diving (Cisneros-Montemayor et al., 2013;Gallagher & Hammerschlag, 2011;Vianna et al., 2011;Vianna et al., 2012;Ward-Paige & Worm, 2017). (Hoff et al., 2023;Karlovic et al., 2021;Motta et al., 2024;Quimbayo et al., 2022). ...
Article
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Silky shark (Carcharhinus falciformis) populations in the South Atlantic Ocean are listed as vulnerable under the IUCN. In fact, this species is classified as critically endangered in Brazil under the Ministry of the Environment. The present study reports the first opportunistic sighting of an aggregation of 250–300 silky sharks in the Alcatrazes Archipelago Wildlife Refuge. Aggregation sites are important in the life cycle of silky sharks, and identifying these sites is essential for conservation efforts.
... Elasmobranchs (subclass elasmobranchii)-sharks, rays, and skates (Compagno et al., 2005)-are important to aquatic ecosystems but are currently considered one of the most vulnerable classes of vertebrates (Baum and Worm 2009;Ferretti et al., 2010;Ward-Paige et al., 2012), with nearly a third of all species threatened by extinction . 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., 2005), 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 important to aquatic ecosystems but are currently considered one of the most vulnerable classes of vertebrates (Baum and Worm 2009;Ferretti et al., 2010;Ward-Paige et al., 2012), with nearly a third of all species threatened by extinction . 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., 2005), 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 important to the health of their respective aquatic ecosystems White et al., 2012), but also provide significant ecosystem services to countries, in the form of revenue and/or sustenance (e.g., ecotourism and fisheries) (Gallagher and Hammerschlag 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., 2005), 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 important to the health of their respective aquatic ecosystems White et al., 2012), but also provide significant ecosystem services to countries, in the form of revenue and/or sustenance (e.g., ecotourism and fisheries) (Gallagher and Hammerschlag 2011;Ward-Paige et al., 2012). ...
... 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
Full-text available
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
Full-text available
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.
... Our results showed an increasing abundance trend that may provide insights concerning the recovery potential of lemon shark populations. Data from a non-exhaustive literature-based study present cases of elasmobranch population increase (Ward-Paige et al., 2012). According to that study, the main causes listed for population recovery were the reduction of fishing mortality by traditional fishery management and incidental by-catch, along with shark finning prohibition. ...
... According to that study, the main causes listed for population recovery were the reduction of fishing mortality by traditional fishery management and incidental by-catch, along with shark finning prohibition. In addition, ecosystem-based strategies, such as the creation of shark sanctuaries and restoration of their natural habitat, nature-based education, and species-specific policies of conservation may have contributed to the positive results (Ward-Paige et al., 2012;Ward-Paige and Worm, 2017). ...
... 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.
... 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.
... 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
... 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.
... 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 aptly enumerated by Swenson et al. (2024), abundance estimates and trends serve as essential metrics in conservation and resource management, playing key roles in assessing conservation status (Wilson, Kendall, and Possingham 2011), gauging the impacts of threats or recovery efforts (Jennings 2000;Ward-Paige et al. 2012), and determining quotas (such as allowable biological catch and annual catch limits in fisheries) for managed populations of both target and non-target species. ...
Article
Full-text available
Estimating and understanding the ratio between effective population size (Ne) and census population size (Nc) are pivotal in the conservation of large marine pelagic fish species, including bony fish such as tunas and cartilaginous fish such as sharks, given the challenges associated with obtaining accurate estimates of their abundance. The difficulties inherent in capturing and monitoring these species in vast and dynamic marine environments often make direct estimation of their population size challenging. By focusing on Ne, it is conceivable in certain cases to approximate census size once the Ne/Nc ratio is known, although this ratio can vary and does not always increase linearly, as it is influenced by various ecological and evolutionary factors. Thus, this ratio presents challenges and complexities in the context of pelagic species conservation. To delve deeper into these challenges, firstly, we recall the diverse types of effective population sizes, including contemporary and historical sizes, and their implications in conservation biology. Secondly, we outline current knowledge about the influence of life history traits on the Ne/Nc ratio in the light of examples drawn from large and abundant pelagic fish species. Despite efforts to document an increasing number of marine species using recent technologies and statistical methods, establishing general rules to predict Ne/Nc remains elusive, necessitating further research and investment. Finally, we recall statistical challenges in relating Ne and Nc emphasizing the necessity of aligning temporal and spatial scales. This last part discusses the roles of generation and reproductive cycle effective population sizes to predict genetic erosion and guiding management strategies. Collectively, these sections underscore the multifaceted nature of effective population size estimation, crucial for preserving genetic diversity and ensuring the long‐term viability of populations. By navigating statistical and theoretical complexities, and addressing methodological challenges, scientists should be able to advance our understanding of the Ne/Nc ratio.
... Atualmente, estima-se que um número entre 63 e 273 milhões de tubarões sejam mortos anualmente, correspondendo a uma taxa de exploração entre 6,4% e 7,9% da população de elasmobrânquios. Esse número ultrapassa a taxa de recuperação da população de diversas espécies de tubarões, com média de aproximadamente 4,9% por ano, o que implica na diminuição drástica de populações de diversas espécies (Ward-Paige et al., 2012). ...
Article
Full-text available
Os tubarões e as raias são animais que têm sido gradativamente impactados pelas ações antrópicas. Uma das atividades que tem impactado grandemente esse grupo de peixes é a pesca indiscriminada, como consequência de uma fiscalização ambiental incipiente, da aplicação de nomes comuns a uma série de espécies distintas e o processamento de animais (e.g. decapitação) ainda embarcados, dificultando assim a sua identificação. Aliados a isso, os elasmobrânquios têm características biológicas e reprodutivas complexas que os tornam vulneráveis à atividade antrópica e a sobrepesca, como ciclo de vida longo, maturação sexual tardia e baixa fecundidade. Nesse sentido, nossas premissas seriam de que a conservação efetiva dos elasmobrânquios envolve a sociedade como um todo e seja eficaz no monitoramento adequado de espécies vulneráveis e ameaçadas de extinção. Dessa maneira, o presente projeto teve como objetivo a integração entre Universidade Federal da Paraíba (UFPB) e a sociedade para a disseminação de conhecimentos associados à diversidade de espécies de elasmobrânquios da costa da Paraíba, de seus aspectos biológicos e graus de vulnerabilidade, de modo a promover a sua conservação. Nossa página na plataforma Instagram chegou a cerca de 1500 seguidores e nossas publicações obtiveram individualmente uma média de 150 curtidas e alcançaram aproximadamente 600 contas. O engajamento do público foi significativo e promoveu, além da troca de conhecimentos, uma nova percepção e interesse muito maior no grupo.
... These immense benefits may have fueled the perception among students that shark fishing should continue. On the contrary, studies by suggest that fisherfolks should reduce the rate of fishing for sharks in Ghana, especially in the wake of population decline (Ward-Paige et al., 2012). The perceived economic gains from shark fishing may have favored the positive reaction to shark fishing among students. ...
Article
In Ghana, students have rarely been engaged in shark conservation programs. The study aimed to provide the perceptions and mis- conceptions about sharks among students in Ghana. From the Western region of Ghana, two senior high schools were visited from March to June 2023, and 111 questionnaires were administered to them with the assistance of a resident teacher. Most of these students believe that i) sharks do not eat humankind as food, ii) fishing activities do not affect shark behavior, iii) the decline in fish does not affect the shark population, and iv) fishermen in Ghana face a lot of shark attacks. On perceptions, most of the students perceived that i) shark fishing should not be stopped, ii) shark ecotourism will yield more money than shark fishing, and iii) MPAs will conserve shark population in Ghana. From the study, it was evident that knowledge and attitudes showed a strong positive correlation (r = 0.61). Therefore, incorporating shark related topics into the curricula of schools, taking students on educational tours to the fishing communities, and engaging them in outreach programs will enlighten their knowledge of sharks and foster their awareness of shark conservation and shark ecotourism in Ghana.
... The recovery and management of elasmobranchs requires a multifaceted approach, which includes enacting spatial protections of critical habitat 57 . Species distribution modeling is a tool that can be used to delineate critical habitat, and has been used to assess the effectiveness of spatial protections for highly migratory species such as bull sharks 18 . ...
Article
Full-text available
Coastal ecosystems are highly vulnerable to the impacts of climate change and other stressors, including urbanization and overfishing. Consequently, distributions of coastal fish have begun to change, particularly in response to increasing temperatures linked to climate change. However, few studies have evaluated how natural and anthropogenic disturbances can alter species distributions in conjunction with geophysical habitat alterations, such as changes to land use and land cover (LU/LC). Here, we examine the spatiotemporal changes in the distribution of juvenile bull sharks (Carcharhinus leucas) using a multi-decadal fishery-independent survey of coastal Alabama. Using a boosted regression tree (BRT) modeling framework, we assess the covariance of environmental conditions (sea surface temperature, depth, salinity, dissolved oxygen, riverine discharge, Chl-a) as well as historic changes to LU/LC to the distribution of bull sharks. Species distribution models resultant from BRTs for early (2003–2005) and recent (2018–2020) monitoring periods indicated a mean increase in habitat suitability (i.e., probability of capture) for juvenile bull sharks from 0.028 to 0.082, concomitant with substantial increases in mean annual temperature (0.058°C/yr), Chl-a (2.32 mg/m³), and urbanization (increased LU/LC) since 2000. These results align with observed five-fold increases in the relative abundance of juvenile bull sharks across the study period and demonstrate the impacts of changing environmental conditions on their distribution and relative abundance. As climate change persists, coastal communities will continue to change, altering the structure of ecological communities and the success of nearshore fisheries.
... Abundance estimates and trends are also key metrics for conservation and management and are commonly used to assess conservation status (Wilson et al., 2011), quantify the impacts of threats and/or recovery efforts (Jennings, 2000;Magera et al., 2013;Ward-Paige et al., 2012), and scale regulated harvest quantities (e.g., allowable biological catch, annual catch limits) for managed populations of target and non-target species. Consequently, a wide range of methods have been developed for estimating population abundance (McCauley et al., 2012;Schwarz & Seber, 1999;Wilson & Delahay, 2001). ...
Article
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Obtaining robust estimates of population abundance is a central challenge hindering the conservation and management of many threatened and exploited species. Close-kin mark-recapture (CKMR) is a genetics-based approach that has strong potential to improve the monitoring of data-limited species by enabling estimates of abundance, survival, and other parameters for populations that are challenging to assess. However, CKMR models have received limited sensitivity testing under realistic population dynamics and sampling scenarios, impeding the application of the method in population monitoring programs and stock assessments. Here, we use individual-based simulation to examine how unmodeled population dynamics and aging uncertainty affect the accuracy and precision of CKMR parameter estimates under different sampling strategies. We then present adapted models that correct the biases that arise from model misspecification. Our results demonstrate that a simple base-case CKMR model produces robust estimates of population abundance with stable populations that breed annually; however, if a population trend or non-annual breeding dynamics are present, or if year-specific estimates of abundance are desired, a more complex CKMR model must be constructed. In addition, we show that CKMR can generate reliable abundance estimates for adults from a variety of sampling strategies, including juvenile-focused sampling where adults are never directly observed (and aging error is minimal). Finally, we apply a CKMR model that has been adapted for population growth and intermittent breeding to two decades of genetic data from juvenile lemon sharks (Negaprion brevirostris) in Bimini, Bahamas, to demonstrate how application of CKMR to samples drawn solely from juveniles can contribute to monitoring efforts for highly mobile populations. Overall, this study expands our understanding of the biological factors and sampling decisions that cause bias in CKMR models, identifies key areas for future inquiry, and provides recommendations that can aid biologists in planning and implementing an effective CKMR study, particularly for long-lived data-limited species.
... Some oceanic shark species, such as the oceanic whitetip shark and silky shark, are commonly caught as bycatch in the Atlantic Ocean but lack stock assessments [10,13]. Robust fisheries management frameworks require more information on the fisheries interactions and life histories of these species [14][15][16], whereas resource-limited management approaches require the identification of critical habitats or aggregation sites worthy of protection or restoration [17]. For migratory oceanic sharks, those sites can include areas where individuals exhibit mating and/or feeding site fidelity [18], which are important life-history criteria for designating important shark and ray areas (ISRAs) [19]. ...
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Fisheries-independent data on the diversity, relative abundance, and demographic structure of poorly studied, threatened oceanic sharks are absent from much of the western North Atlantic Ocean, where multiple oceanic shark species have experienced significant population declines. Resource-limited management approaches require the identification of critical habitats or aggrega-tion sites worthy of protection and enforcement. Data were collected on oceanic sharks using pelagic longline surveys, targeted baiting, and opportunistic encounters in oligotrophic open-ocean habitats of northeastern Exuma Sound (NES), The Bahamas. The oceanic epipelagic shark community was also characterized using targeted baiting off Columbus Point, Cat Island (CI), a seamount north of San Salvador (SSSM), and the northeastern tip of Mayaguana. Pelagic longline surveys suggested that the relative abundance of sharks at NES was low (shark catch-per-unit-effort: 0.0007 sharks hook −1 h −1 ; 2.3 sharks per 1000 hooks). Silky sharks Carcharhinus falciformis, particularly juveniles (134 ± 39 cm stretched total length; mean ± SD STL), were the most common. Targeted baiting suggested oceanic whitetip sharks C. longimanus were abundant at CI, where large adults (245 ± 23 cm STL), most of which were females (83.8%, n = 98 of 117) that were gravid (65.7%; n = 46 of 70 assessed for pregnancy), dominated the aggregation. Many (20.5-26.5%, n = 24-31 of 117 depending on assumptions regarding tag loss) were recaptured or resighted at CI for up to five years. Silky sharks dominated catches at SSSM. Oceanic sharks, particularly adults, were sometimes caught or observed alongside short-finned pilot whales Globicephala macrorhynchus or tunas. Although The Ba-hamas offers threatened oceanic sharks refuge from fishing across its entire jurisdiction, these data suggest that some fixed features, including sites such as CI and potentially SSSM, are important aggregation sites with high regional conservation value and should be prioritized by fisheries managers and enforcement officials. Citation: Talwar, B.S.; Brooks, E.J.; Abercrombie, D.L.; Anderson, B.; Bond, M.E.; Brooks, A.M.L.; Chapman, D.D.; Clementi, G.M.; Fields, C.Y.A.; Gelsleichter, J.; et al.
... Concerning TCEs, some findings in bony fish have indicated developmental, genotoxicity, mutagenicity, and reproductive effects for some TCEs, such as titanium and rubidium and some REE, such as lanthanum and praseodymium, as well as potential trophic web biomagnification, directly affecting not only individual health but also ecosystem dynamics (Campbell et al., 2005;Dubé et al., 2019;Zhao et al., 2021;Santos et al., 2023). Extrapolating these findings to cartilaginous fish, significant physiological and ecological effects of TCEs in this highly vulnerable taxonomic group are probable, due to certain specific life-history traits, such as slow maturation rates, low fecundity, long lifespans, and mostly meso-and top predator positions (Ward-Paige et al., 2012). ...
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Human activities have significantly impacted our natural environments, resulting in extensive degradation, with chemical contamination emerging as a critical concern. This type of pollution has far-reaching implications, affecting ecological health and socioeconomic dimensions. The concept of “contaminants of emerging concern” encompasses newly recognized environmental pollutants, highlighting their diverse and often understudied effects. This category includes microplastics, antibiotics, pharmaceuticals, and metals, among others, many of which lack adequate regulations and understanding of their ecological and human impacts. A subset of these pollutants, termed Technology-Critical Elements (TCEs), holds significance in high-tech industries but also poses environmental challenges due to increased extraction, manufacturing, and disposal. Aquatic environments, the ultimate chemical contaminant sinks, require heightened attention with regard to TCE dynamics and effects. Despite increasing research on TCEs in various aquatic taxa, a lack of comprehensive data hinders further knowledge assessments. In this scenario, fish, key environmental health indicators and links to human contamination, demand focused studies. Cartilaginous fish, specifically, are often overlooked, although ecologically and economically significant, warranting research into TCE effects. This type of research displays the potential to shed light on TCE dynamics, ecological outcomes, and guide conservation strategies for these species and their habitat, also aligning with the One Health concept, acknowledging the interconnectedness of humans, animals, and the environment and contributing to SDG goals, underpinning marine ecosystem conservation.
... Las variables seleccionadas estuvieron asociadas a la ubicación geográfica (región, zona de pesca o distancia a la costa), estacionalidad (mes) y otras al poder de pesca (número de tripulantes o capacidad de bodega). Se seleccionó el modelo más parsimonioso y se basó en plantear un modelo nulo que incluyera todos los factores que se consideraron relevantes para el análisis (incluidas las interacciones) y posteriormente seleccionar sólo aquellas variables que explicaron más del 5% de la desviación total, tal como consideran distintos autores (Soto et al., 2009;Pons et al., 2010;Walter, 2012;Pons & Domingo, 2014). Por otro lado, también se realizó un análisis de diagnóstico sobre los residuales del modelo seleccionado. ...
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Se determinaron algunos indicadores poblacionales de tiburón diamante (Isurus oxyrinchus) y tiburón azul (Prionace glauca) con información biológico-pesquera recolectada a lo largo del litoral peruano en el periodo 1996-2018. Los mayores desembarques de estas especies se registraron en la zona sur con el arte de pesca espinel, siendo el tiburón azul la especie predominante. A partir de la distribución de frecuencia de tallas, se determinó que el 70% de ejemplares de tiburón azul capturados en la zona norte-centro están sobre la TMC (>160 cm de LT) en tanto para el tiburón diamante se registró un menor porcentaje de ejemplares con tallas sobre la TMC (>170 cm de LT) en ambas zonas. Las series de CPUE mostraron tendencia negativa, observando una caída más pronunciada en el caso del tiburón diamante. La herramienta FishPath dio un listado de opciones de manejo, siendo las más recomendables limitar el esfuerzo y establecer vedas temporales, a fin de reducir la presión pesquera ejercida sobre ambas especies de tiburones.
... The extinction risk for sharks is largely attributed to overfishing (Worm et al., 2013), which is exacerbated by their relatively slow growth and low reproductive rates, making them particularly vulnerable to population declines (Hoenig & Gruber, 1990). Reversal of these declines for many species will require a variety of approaches, including protections of essential habitats, long-term monitoring programs, and reductions in fishing mortality (Ward-Paige et al., 2012). The shift into catch-and-release practices by many recreational anglers allows for national tagging programs (e.g., NOAA Fisheries Apex Predator Program) and local tagging initiatives (e.g., Center for Sportfish Science and Conservation Shark Tagging Program) to provide long-term monitoring on a large scale that otherwise would not be monetarily or physically feasible (Gibson et al., 2019). ...
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Post‐release mortality threatens shark populations already imperiled by overfishing, capture stress, and a changing climate. Few studies have quantified post‐release mortality for sharks captured in land‐based recreational fisheries. From 2018 to 2021, a land‐based shark post‐release mortality study was conducted and identified water temperature and species‐specific behavior as contributing factors to post‐release mortality. The purpose of this study was to estimate the effectiveness of disseminating the recommendation for best practices to recreational shark anglers and to determine if this information influenced angler behavior. Awareness of our post‐release mortality study influenced an angler's likely release behavior, with an increase in sharks landed in the water and corresponding decrease of sharks landed on dry sand. This study demonstrated direct evidence of conservation‐based changes in angler behavior following effective research communication and involvement of anglers in research. Outreach and engagement initiatives aimed at providing best handling practices to recreational anglers should be easily digestible, widely available, and an important component of future research.
... The present study found that trawlers account for relatively high catch volumes of elasmobranchs with low selectivity. Management efforts can therefore be employed to restrict fishing effort (in terms of number of vessels or trips; Ward-Paige et al., 2012), to mitigate by catch (through gear regulations and safe release protocols; Gupta et al., 2020a) and to restrict the use of certain gears in important habitat sites. Fishing effort of trawlers can also be reduced by closing areas during critical seasons for elasmobranchs and better enforcement of depth and fishing zone regulations, to reduce catch of vulnerable species. ...
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Although elasmobranchs (sharks and rays) are highly threatened by fisheries, there are few studies that examine gear and fishery effects on catch composition and abundance across India, one of the top elasmobranch fishing nations globally. We assessed elasmobranch diversity, abundance, catch rates and fishery characteristics using landing surveys in Malvan on the central‐western coast of India, a major multi‐gear, multi‐species fishing centre, over three sampling periods from February 2018 to March 2020. We sampled 3145 fishing trips and recorded 27 elasmobranch species, of which nearly half are categorised as “Threatened” by the IUCN. In addition, we documented historical records by compiling information from identification guides, research papers, articles and reports. During the study period, the catch was dominated by small‐sized coastal species like the spadenose shark (Scoliodon laticaudus) and the scaly whipray (Brevitrygon walga). Trawlers accounted for 64.9% of the catch, highest by number, and captured smaller‐sized individuals. Nonetheless, artisanal and gillnet fisheries had higher catch per unit effort (CPUE) for rays (5.1 ± 1.0) and sharks (10 ± 1.0), respectively, and captured significantly larger‐sized individuals. Through generalised linear models, we found seasonal, gear and fishery effects on the abundance and size of commonly caught species. The presence of neonates and gravid females of multiple species also suggests nursery grounds in this region. Historically, 141 species have been recorded in this region, and a comparison with current catch suggests a shift in elasmobranch community structure and potential mesopredator release. This study emphasises the importance of gear and species‐specific research for conservation planning at the local level and suggests the need for management strategies with fisher cooperation.
... Although the term is misleading and holds no legal obligation to refer to any particular species (Ciconte, 2014), it has historically been used in Australia for shark fillets sold at market since the mid-1920s where it originated in relation to the Southern Australian/Victorian gummy shark fishery (Ciconte, 2014). This fishery, once considered to be well managed and sustainably fished (Ward-Paige et al., 2012), is now of concern due to by-catch and depleting stock structure (Petrolo et al., 2021). ...
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Flake and shark samples were purchased from outlets in several coastal Australian regions and genetically barcoded using the cytochrome oxidase subunit 1 (CO1) gene to investigate labelling reliability and species‐specific sources of ambiguously labelled fillets. Of the 41 shark fillet samples obtained, 23 yielded high‐quality CO1 sequences, out of which 57% (n = 13) were labelled ambiguously (misleading) and 35% (n = 8) incorrectly. In contrast, barramundi fillets, which are widely available and sought after in Australian markets, were shown to be accurately labelled. Species identified from shark samples, including the shortfin mako (n = 3) and the scalloped hammerhead (n = 1), are assessed by the IUCN as endangered and critically endangered, respectively, with several others classified as vulnerable and near threatened.
... In order to assess the status of threatened species, it is critical to evaluate the influence of management measures (Ward-Paige et al., 2012). In the present study, we aim to explore the spatial and temporal population dynamics of critically endangered taxa (common skate species complex) of high priority conservation interest, against the backdrop of changes in fisheries management measures using publicly available fisheries-independent trawl survey data. ...
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Aim The critically endangered common skate species complex is a large‐bodied and long‐lived batoid, which has experienced local extirpations and population declines over the past century mainly due to overfishing. Due to its decline, fisheries management measures were introduced to prevent further decline and fragmentation of populations. For example, in 2009, a landings prohibition was introduced in the European Union, which banned the retention of common skate onboard commercial fishing vessels with captured individuals to be discarded. We aimed to explore the spatial and temporal population dynamics of the common skate species complex, against the backdrop of changes in fisheries management measures. Location Northeast Atlantic Ocean. Methods We used publicly available fishery‐independent trawl survey data from several regions of the Northeast Atlantic shelf to examine trends in incidence and abundance for the common skate species complex. We also constructed a species distribution model to identify changes in the spatio‐temporal distribution of the common skate. Results A sustained increase in the common skate species complex was evident in several areas of its distribution. An increase was observed in five separate trawl surveys encompassing distinct regions of its distribution. Despite the observed increase, little evidence of recolonizing previously extirpated areas was evident. Main Conclusions The findings demonstrate the effectiveness of fisheries management measures in contributing to an increase in the common skate species complex. Such measures may also be effective if applied to numerous other batoid species currently threatened with extinction.
... Sin embargo, la disposición espacial durante diferentes etapas del ciclo de vida, el interés comercial coyuntural y las características particulares de cada especie y pesquería en la que son capturadas hace que no todas las poblaciones de condrictios tengan la misma vulnerabilidad. En este sentido también se han documentado casos de estabilidad en poblaciones de condrictios sometidos a explotación comercial (Walker 1997, Francis 1998 Ministry of Fisheries of New Zeland 2011, Barnett et al. 2012, Carlson et al. 2012, Ward-Paige et al. 2012). ...
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En el presente trabajo se estudiaron las características de historia de vida en cuanto a edad, crecimiento, longevidad y talla-edad de madurez del Tiburón gatuzo, Mustelus schmitti, en el Golfo San Matías, Argentina. La edad y crecimiento fueron calculadas a partir de la lectura de bandas en secciones vertebrales evaluando cinco modelos de crecimiento. El rango de tallas registrado en los muestreos de los desembarques comerciales fue de 37 y 89 cm de longitud total (LT) para machos y entre 39 y 106 cm para hembras. Las edades observadas fueron entre 1 a 15 años para machos y 1 a 21 años para hembras. El modelo de von Bertalanffy de 2 fases para ambos sexos juntos fue seleccionado como el más adecuado según el ajuste estadístico y el criterio biológico, estimándose los siguientes parámetros: edad a la talla cero t0= -3,56 años (talla de nacimiento L0= 35,7cm); talla asintótica L∞= 103,12cm; y coeficiente de crecimiento K= 0,12 años-1. La longevidad estimada fue de 21 años. Los machos y hembras maduran a una edad y talla media similar de 5,6 años y LT50% de 66,9 cm. No se encontraron diferencias entre sexos en las curvas de crecimiento. Este estudio contribuye al conocimiento de las características de historia de vida de la especie en el sur del Atlántico sudoccidental (ASO) reportando que M. schmitti tiene un crecimiento moderado, es una de las especies más longevas dentro del género y tiene una edad media de madurez temprana que representa aproximadamente un cuarto de la longevidad estimada.
... There is now a growing interest in the retention and trade of non-targeted elasmobranchs. This is partially due to the overexploitation of other marine resources (Ward-Paige et al., 2012). Furthermore, the exponential increase on elasmobranch meat demand, especially in low and low-middle income countries (Karnad et al., 2020) seems to contribute to the observed shift in bycatch fate, as well as the market demand for shark fins in Asian countries (Lam and Sadovy de Mitcheson, 2011). ...
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Sharks and rays are among the most threatened vertebrates, mostly due to commercial fisheries. Data on incidental capture is sparse, but it is estimated that about 50% of reported global catches of elasmobranchs are from bycatch. Elasmobranchs are captured in a variety of fishing gear throughout the world. One promising strategy to minimize incidental catches is the release of live sharks and rays. However, so far, no critical analysis had been carried out to assess the importance of release as a measure to mitigate the impacts of bycatch. Results indicated that despite onboard releases being cited in Plans of Action (along ZEEs) and recommendations/regulations of Regional Fisheries Management Commissions (in international waters), this measure is treated as secondary and has voluntary adherence, which can significantly reduce its efficiency. Moreover, among the Best Fishing Practice Manuals currently available, although release is cited as a priority, most of them do not consider the dynamics of the location/fishing modality for which it was developed. A change on how release is perceived is needed to prioritize this conservation strategy, as well as its potential as a social tool to reduce the impacts of bycatch on sharks and rays.
... 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 . ...
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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.
... 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
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
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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.
... Landings surveys should clarify whether elasmobranchs are targeted, bycatch, or by-product to guide management (Gupta et al., 2020) and collect biological information and catch locations to determine critical habitats during different life stages and seasons (Ward-Paige et al., 2012;Heupel et al., 2018). Analysis of DNA from tissue samples could help identify cryptic and "lost" species (Feitosa et al., 2018;Clark-Shen et al., 2021). ...
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In Southeast Asia, elasmobranchs are particularly threatened. We synthesized knowledge from the peer‐reviewed and gray literature on elasmobranchs in the region, including their fisheries, status, trade, biology, and management. We found that 59% of assessed species are threatened with extinction and 72.5% are in decline; rays were more threatened than sharks. Research and conservation is complicated by the socioeconomic contexts of the countries, geopolitical issues in the South China Sea, and the overcapacity and multispecies nature of fisheries that incidentally capture elasmobranchs. The general paucity of data, funds, personnel, and enforcement hinders management. Reduced capacity in the general fishery sector and marine protected areas of sufficient size (for elasmobranchs and local enforcement capabilities) are among recommendations to strengthen conservation.
... 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. ...
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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.
... 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). ...
Article
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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. ...
Article
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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. ...
Preprint
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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.
... 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. ...
... 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
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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
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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.
... 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
Thesis
Elasmobranch populations are decreasing rapidly worldwide due to anthropogenic exploitation such as commercial fishing, where targeted shark fisheries and accidental bycatches harvest more than 100 millions sharks yearly. With constantly changing biodiversity, species composition and conservational statuses of marine megafauna, frequent research and constant updates on species distribution and abundances in an area is highly necessary for initiating and maintaining conservational actions. Ecotourism operations such as shark-cage diving operators strongly rely on sustainable and functioning ecosystems and wildlife in order to utilize these for tourism purposes. The aim of this study was to investigate the effect of parameters influencing presence and abundances of sympatric species around a shark-cage diving vessel in Gansbaai, South Africa. Significant relationships between sea surface temperature and abundance was found for Carcharodon carcharias 27 (t=-4,42, p<0,05), Carcharhinus brachyurus (t= 8,46, p<0,05) and Arctocephalus pusillus (t = 2,7, p<0,05) but not for Bathytoshia brevicaudata (t= 0,15, p>0,05). These relationships revealed unexplained changes in abundance caused by additional parameters. Interspecific interactions primarily between Carcharhinus brachyurus and Carcharodon carcharias was found to affect the abundance of the respective species. The abundance of C. brachyurus were lower in the presence of C. carcharias longer than 4 m TL, compared to in the presence of smaller (<4 m TL) individuals or complete absence of C. carcharias. A probabilistic co-occurrence analysis and a Generalized Additive Model (GAM) were used to investigate interspecific interactions between these two species, supporting the hypotheses of species-and size-regulated hierarchies around a shark-cage diving vessel. The co-occurrence analysis also suggested negative associations between C. brachyurus and large C. carcharias (>4 m TL, P Low = 0,008 and P High = 0,999). The GAM revealed significant increases in C. brachyurus abundance over the duration of the deployments in absence of C. carcharias (edf= 8,79, p<0,005). In the presence of C. carcharias no significant change in C. brachyurus abundance was found (edf= 2,48, p= 0,101), however, a strong trend in declining abundance over time was revealed. These findings are most important to further understand interspecific interactions of sharks and their abundances around ecotourism vessels, and are hoped to contribute to future research enabling sustainable shark populations and ecotourism.
Preprint
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Delineating the spatial ecology of elasmobranchs is an important precursor to their effective management. Establishing long-term patterns in the habitat use of several threatened species can focus management to yield increased conservation benefits. We completed 738 transects on 16 reef sites off the coast of southern Mozambique to record encounters with elasmobranch species and 12 environmental and spatiotemporal parameters (location, time, day, tide and range, cloud cover, visibility, lunar phase, temperature, current strength, and direction, transect duration). The influence of the measured parameters on the visit frequencies of nine regularly (> 20 / year) encountered elasmobranch species ( Carcharhinus amblyrhynchos, Triaenodon obesus, Stegastoma tigrinum, Neotrygon kuhlii, Himantura jenkinsii, Taeniura meyeni, Mobula kuhlii, Mobula alfredi, Mobula birostris ) were estimated using multivariate models. All species, bar H. jenkinsii , frequented specific reef sites. Counts were generally highest in summer. Three species ( M. birostris, M. kuhlii, S. tigrinum ) counts peaked in winter. T. obesus and M. alfredi tended to frequent reefs during high tides, M. kuhlii during slack tides, N. kuhlii during low tides and C. amblyrhynchos when the tidal range was high. Counts of M. alfredi were highest during full moons and M. kuhlii during full, half, and new moons. Non-Metric Multidimensional Scaling (NMDS) indicated that species responses to the measured parameters grouped taxonomically. Environmental influences resulted in daily, monthly, and seasonal patterns of reef use. Our results indicate that specific elasmobranch species routinely congregate on specific reef sites and that management of these sites could promote several threatened populations.
Article
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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.
Article
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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.
Preprint
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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.
Article
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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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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.
Article
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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 Rafinesque 1810) 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.
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.
Article
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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.
Article
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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.
Article
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Most arguments invoked so far by the scientific community in favour of shark conservation rely on the ecological importance of sharks, and have little impact on management policies. During a 57-month study, we were able to individually recognise 39 sicklefin lemon sharks that support a shark-feeding ecotourism activity in Moorea Island, French Polynesia. We calculated the direct global revenue generated by the provisioning site, based on the expenses of local and international divers. The total yearly revenue was around USD5.4 million and the 13 sharks most often observed at the site had an average contribution each of around USD316 699. Any one of these sharks represents a potential contribution of USD2.64 million during its life span. We argue that publicising economic values per individual will be more effective than general declarations about their ecological importance for convincing policy makers and fishers that a live shark is more valuable than a dead shark for the local economy. Studies monitoring the potential negative ecological effects of long-term feeding of sharks should, however, be conducted to ensure these are also considered. Besides declarations about the non-consumptive direct-use value of sharks, as promoted by ecotourism, the calculation of their other economic values should also benefit shark conservation.
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The elasmobranch fauna of Everglades National Park was studied using longline, gillnet, and rod and reel surveys. Thirteen species of elasmobranchs were identified including three species not previously reported in the park. Species richness was highest in the areas with the greatest influence of marine waters from the Gulf of Mexico and lower in estuarine areas and those subject to periods of hypersalinity. Most elasmobranch species were recorded as juveniles, with at least three species occurring as neonates, and there were few adults of any species. Electivity indices for salinity, temperature, and depth were calculated for Carcharhinus leucas (Valenciennes, 1841), Carcharhinus limbatus (Valenciennes, 1841), Ginglymostoma cirratum (Bonnaterre, 1788), and Negaprion brevirostris (Poey, 1868), and indicated possible habitat partitioning based on these environmental characteristics. Tag-recapture data suggested that N. brevirostris may have a high level of residency and probably remains inside the park for long periods, while all other species showed movements into and out of the park on a regular basis. Results demonstrate the utility of the park for the conservation and management of elasmobranch species and the need to consider how future changes to the environment will affect this important group of predators.
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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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Theoretical models of coastal shark populations have remained largely unchanged since the 1960s despite limitations in applicability to many species. Smaller bodied coastal species are poorly represented by the current models. A new theoretical model is proposed to represent those species that spend most or all of their life within nearshore waters but do not show use of discrete nursery areas. Description of this new model outlines the importance of nearshore areas to these smaller species. While all coastal shark populations are susceptible to environmental and anthropogenic impacts, species that fit the new model are more vulnerable to varying coastal processes, habitat degradation, and fishing pressure than are species that use nearshore areas for only part of their life-span. The dynamic nature of nearshore areas and their proximity to human populations present all sharks that occur in them with a range of advantages and disadvantages. This paper reviews how different species utilise nearshore areas and how they overcome the challenges they face in inhabiting these areas. Improving and expanding theoretical models of coastal shark populations will provide a better understanding of how sharks use nearshore environments and assist in making conservation and management decisions for these regions.
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Twenty-four years (1977–2000) of competitive shore angling catch and effort data from the KwaZulu-Natal Coastal Anglers Union for the province of KwaZulu-Natal were analysed. Of a minimum of 117 species recorded, the most commonly caught species were dusky shark (Carcharhinus obscurus) (26%), milk shark (Rhizoprionodon acutus) (18%) and shad (Pomatomus saltatrix) (10%). By weight, the top species were dusky shark (34%) and diamond ray (Gymnura natalensis) (19%). All the above species showed considerable inter-annual variation in their respective contributions to annual catch. Probably as a result of changes in fishing patterns, dusky shark and milk shark showed a general decline in percentage contribution to catch over the period, while contributions of lesser guitarfish (Rhinobatos annulatus), giant guitarfish (Rhynchobatus djiddensis), diamond ray (Gymnura natalensis) and brown ray (Himantura gerrardi) increased. Mean overall annual cpue by number and weight showed a non-significant increase over the period, w