ArticleLiterature Review

Patterns and ecosystem consequences of shark declines in the ocean

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Abstract

Whereas many land predators disappeared before their ecological roles were studied, the decline of marine apex predators is still unfolding. Large sharks in particular have experienced rapid declines over the last decades. In this study, we review the documented changes in exploited elasmobranch communities in coastal, demersal, and pelagic habitats, and synthesize the effects of sharks on their prey and wider communities. We show that the high natural diversity and abundance of sharks is vulnerable to even light fishing pressure. The decline of large predatory sharks reduces natural mortality in a range of prey, contributing to changes in abundance, distribution, and behaviour of small elasmobranchs, marine mammals, and sea turtles that have few other predators. Through direct predation and behavioural modifications, top-down effects of sharks have led to cascading changes in some coastal ecosystems. In demersal and pelagic communities, there is increasing evidence of mesopredator release, but cascading effects are more hypothetical. Here, fishing pressure on mesopredators may mask or even reverse some ecosystem effects. In conclusion, large sharks can exert strong top-down forces with the potential to shape marine communities over large spatial and temporal scales. Yet more empirical evidence is needed to test the generality of these effects throughout the ocean.

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... Historical naturalist accounts, exploratory fisheries surveys, and historical photographs compared to modern scientific records have been used to document the effect of exploitation on sharks in the last 2 centuries (Ferretti et al. 2010, Martin et al. 2016), including the local or functional extinction of historically abundant shark species from coral reef ecosystems and large oceanic expanses (Baum & Myers 2004, McClenachan 2009, Luiz & Edwards 2011, Ferretti et al. 2013). Yet in many cases, these are likely tail ends of depletions that began long before records began. ...
... There is evidence that top-level predator sharks can play important roles in marine ecosystems (Heithaus et al. 2008, Ferretti et al. 2010, Estes et al. 2016, Roff et al. 2016a, and their removal through fisheries has often coincided with strong population responses of lower-level elasmobranchs. Ecological roles of elasmobranchs include top-down control of prey , Heithaus et al. 2008, nutrient cycling (Williams et al. 2018), facultative scavenging (Dudley et al. 2000, Drymon et al. 2019), biocontrol of invasive species (Diller et al. 2014), habitat modification (O' Shea et al. 2012), and possibly removal of weak and diseased individuals . ...
... Substantial knowledge gaps exist for the contextdependence of ecological roles, which is important in terms of quantifying the consequences of elasmobranch removal or recovering elasmobranch populations. For example, we have little understanding of the role of fear in driving many of the large-scale and long-term ecosystem changes attributed to sharks (Heithaus et al. 2008, Ferretti et al. 2010. Also unknown are factors affecting population sizes of key prey taxa (i.e. ...
Article
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Over the past 4 decades there has been a growing concern for the conservation status of elasmobranchs (sharks and rays). In 2002, the first elasmobranch species were added to Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Less than 20 yr later, there were 39 species on Appendix II and 5 on Appendix I. Despite growing concern, effective conservation and management remain challenged by a lack of data on population status for many species, human−wildlife interactions, threats to population viability, and the efficacy of conservation approaches. We surveyed 100 of the most frequently published and cited experts on elasmobranchs and, based on ranked responses, prioritized 20 research questions on elasmobranch conservation. To address these questions, we then convened a group of 47 experts from 35 institutions and 12 countries. The 20 questions were organized into the following broad categories: (1) status and threats, (2) population and ecology, and (3) conservation and management. For each section, we sought to synthesize existing knowledge, describe consensus or diverging views, identify gaps, and suggest promising future directions and research priorities. The resulting synthesis aggregates an array of perspectives on emergent research and priority directions for elasmobranch conservation.
... In pristine, unfished regions, sharks are abundant and diverse [40]. As highly successful top and middle predators, they survived the several mass, global extinctions and, through radial evolution, adapted to new ecological niches [50][51][52]. ...
... Thus, over the past 500 million years, they became deeply woven into the aquatic ecosystems of the planet. Industrial fishing has resulted in a large-scale ecological transformation, not only in terms of the size of individuals and the relative abundance of species, but also community biomass [17,21,40,43,53]. The removal of top predators causes alternating increases and declines in the abundance of lower levels on the food chain, an effect called a 'trophic cascade' [17]. ...
... The depletion of top predators, therefore, causes deep disruption in ecological communities that is widespread and long-lived [40,44]. Over more than seven decades, in-dustrial shark removal has resulted in major shifts in biomass and size composition in all oceans [17,40,43]. ...
Article
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The expanding shark fin market has resulted in intensive global shark fishing and with 90% of teleost fish stocks over-exploited, sharks have become the most lucrative target. As predators, they have high ecological value, are sensitive to fishing pressure, and are in decline, but the secretive nature of the fin trade and difficulties obtaining relevant data, obscure their true status. In consumer countries, shark fin is a luxury item and rich consumers pay high prices with little interest in sustainability or legal trade. Thus, market demand will continue to fuel the shark hunt and those accessible to fishing fleets are increasingly endangered. Current legal protections are not working, as exemplified by the case of the shortfin mako shark, and claims that sharks can be sustainably fished under these circumstances are shown to be misguided. In the interests of averting a catastrophic collapse across the planet’s aquatic ecosystems, sharks and their habitats must be given effective protection. We recommend that all sharks, chimaeras, manta rays, devil rays, and rhino rays be protected from international trade through an immediate CITES Appendix I listing. However, a binding international agreement for the protection of biodiversity in general is what is needed.
... Catch rates and distribution pattern of the silky shark, Carcharhinus falciformis, Catch rates and distribution pattern of the silky shark, Carcharhinus falciformis, caught by the Taiwanese large-scale longline fishery in the Indian Ocean caught by the Taiwanese large-scale longline fishery in the Indian Ocean 1. Introduction E lasmobranchs (sharks, rays, and skates) are crucial to the marine ecosystem [1,2]. These apex predators balance trophic interactions [3] and sustain the dynamics [4] of the marine community [2,5,6]. ...
... These apex predators balance trophic interactions [3] and sustain the dynamics [4] of the marine community [2,5,6]. Changes in the abundance of top predators influence the composition of species in the food web [1,7,8]. Numerous studies [1,9e11] have demonstrated that reductions in the number of sharks and rays lead to a trophic cascade that affects every level of the food chain. ...
... These species are known to structure marine ecosystems shaping the marine food web [2,7,8]. Dwindling in the size of the population of such species breaks the food web connectivity of other species [9,10], resulting in trophic cascades through top-down effects [8,11,12]. Consequently,megafauna losses negatively impact entire marine ecosystems' structure, function, and productivity [9,13,14]. Furthermore, megafauna species are migratory animals that travel for long distances, therefore, face similar threats globally [15]. ...
... Under the same Act, three sanctuaries for dolphin conservation were declared, covering a 32 km 2 area along the eastern Sundarbans mangrove.To implement the CBD, the Bangladesh government formulated the Bangladesh Biodiversity Act (2017) to conserve biodiversity and ensure sustainable utilization of biodiversity and related resources. Biodiversity refers to the species, genetic, and ecosystem diversity that exists in and is a part of the overall environment within terrestrial, aquatic, or marine environments [Chapter I, 2 (11)]. This act has a provision prescribing declaration of 'Biodiversity Heritage Site' that are rich in biodiversity [Chapter 6(32)] and prohibit activities that are considered harmful to environmentally endangered species [Chapter 6, section 33)]. ...
Article
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This study investigates the legalregime governing marine megafauna conservation in Bangladesh. The study found thatlack of data, weak domestic institutional structure, ineffective implementation, unsuitable enforcement agencies, and poor public policies limit the protection of the marine megafauna of conservation interest. In many cases, domestic legislation is not compatible with Bangladesh's international treaty obligations and duties. The study advocates significant legal reforms and a whole-of-government approach to strengthen the institutional framework for conserving marine megafauna in the Bay of Bengal. The strong coordination among public agencies, academics, and communities can build up an adequate institutional framework. Public policy and legal reform should focus on mitigating bycatch and reducing bycatch mortality, managing threats originating from non-fishing sources, and halting habitat degradation.
... Understanding the trophic ecology of keystone species is essential to determine their role in marine ecosystems (Ferretti, Worm, Britten, Heithaus, & Lotze, 2010;Dulvy et al., 2014). Deep-sea sharks are considered important predators on marine food webs playing an important role in top-down controls on the dynamics of many ecosystems (Wetherbee, Cortés, & Bizzarro, 2012). ...
... Deep-sea sharks are considered important predators on marine food webs playing an important role in top-down controls on the dynamics of many ecosystems (Wetherbee, Cortés, & Bizzarro, 2012). During the last decades, elasmobranchs have become the focus of ecological studies (Ferretti, et al., 2010;Dulvy, et al., 2014;Navia, Mejia-Falla, Lopez-Garcia, Giraldo, & Cruz-Escalona, 2017). Nevertheless, only a few studies have focused on the interactions among sympatric elasmobranchs species, which is essential to understand how elasmobranchs coexist in the same habits (Albo-Puigserver et al., 2015;Barria, Navarro, & Coll, 2018;Yemisken, Navarro, Forero, Megalofonou, & Eryilmaz, 2019). ...
Conference Paper
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Feeding habits, diets and trophic relationships among three demersal sharks (Galeus melastomus Rafinesque, 1810; Etmopterus spinax (Linnaeus, 1758); and Scyliorhinus canicula (Linnaeus, 1758)) from the Porcupine Bank, Northeast Atlantic were studied. The stomach content analysis revealed differences between the diet of the three species, with a clear preference for benthonic preys in the case of S. canicula, and benthopelagic preys in the case of E. spinax and G. melastomus. The results of this study provide new knowledge about the ecological role of these species in the Porcupine Bank and will be of vital importance for their management and conservation of these species.
... Au niveau mondial, les attaques et les attaques mortelles répertoriées sont également en augmentation. Cependant, les populations de requins le plus fréquemment responsables d'attaques que sont le grand requin blanc, le requin tigre et le requin bouledogue [37,54] sont en baisse [15,17,31,40,42]. La démographie des populations locales du requin tigre et du requin bouledogue, qui sont les prédateurs le plus fréquemment impliqués dans les attaques en Nouvelle-Calédonie est, quant à elle, mal connue. ...
Article
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Background and objectives: Recent shark attacks in New Caledonia have prompted local authorities to elaborate a risk-management plan. The objective of the present paper is to produce detailed data on shark attacks that occurred in New Caledonian waters for the last few decades, as well as on the injuries of the victims, in order to inform rescue and medical services as well as authorities in charge of educating the public and providing security. Methods: Incidents involving sharks and humans in New Caledonia for the last six decades were included into a database. Sharks were tentatively identified to species according to the shape, size and other external characteristics of injuries to the victims, together with witness accounts. The severity of shark bites was evaluated against the scale proposed by A.K. Lentz and co-authors (Am Surg. 2010;76:101-6). Results: Sixty-seven shark-attack cases were recorded in New Caledonia from 1958 to 2020, of which 13 were lethal. The majority of the attacks concerned spearfishers and freedivers collecting invertebrates (58.5% of total). In the last decades, shark attacks may have increased towards bathers, swimmers and snorkelers (18.5%), and people taking part in water sports including surf, kitesurf, windsurf and SUP foil (14%). One scuba diver was also attacked (1.5%). Twenty attacks including 8 lethal ones were ascribed to the tiger shark Galeocerdo cuvier; 14 attacks including 2 lethal ones to the bull shark Carcharhinus leucas; 2 attacks including 1 lethal to the great white shark Carcharodon carcharías. The lethality of attacks was almost one in five, above the global average. Conclusions: Feeding incentive appeared to be a frequent factor triggering attacks. The education of the public should be promoted as a preventive measure aiming to reduce the risk of such accidents.
... Sharks have a fundamental role in maintaining the balance of aquatic ecosystems because, being at higher trophic levels, they can exert a great influence on lower levels [1]. However, they are currently declining worldwide due to overfishing, habitat degradation, climate change, and pollution [2][3][4][5]. This decrease is intensified by their biological characteristics, such as slow growth, late maturity, and few offspring [6]. ...
Article
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Although sharks have a fundamental role in maintaining the balance of aquatic ecosystems, exerting a great influence on lower levels of the food chain, their populations are declining worldwide due, to a large extent, to overfishing. Of the 64 species registered in Ecuador, from January to December 2019, 19 species were recorded in Manta from the 15,455 captured individuals, with the family Carcharhinidae being the most abundant in the catches (69.4%), and the most abundant species was Prionace glauca (57.9%). Regarding threatened species, such as Carcharhinus longimanus, Sphyrna lewini, and Sphyrna zygaena, a greater presence of immature specimens was observed in landings. However, information on the composition and biological aspects of shark species in the Ecuadorian Pacific is very scarce. Therefore, research on the characteristics of life history (age, growth, and maturity) are of utmost importance for the stock assessments that are being exploited, especially in developing countries, where this information is lacking, causing inadequate management of fishery resources.
... Predator species influence prey behaviour and remove prey items from ecosystems, regulating the composition of, and dynamics within prey assemblages [6,7]. Globally, the removal of predators through overfishing can destabilise food webs through mesopredator release and herbivore suppression that leads to altered trophic function [8][9][10]. Knowledge of the effects of predator removal and trophic ecology on reefs remains a contemporary issue due to its conservation implications [11]. ...
Article
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Predatory fishes on coral reefs continue to decline globally despite playing key roles in ecosystem functioning. Remote atolls and platform reefs provide potential refugia for predator populations, but quantitative information on their spatial distribution is required to establish accurate baselines for ongoing monitoring and conservation management. Current knowledge of predatory fish populations has been derived from targeted shallow diver-based surveys (<15 m). However, the spatial distribution and extent of predatory fishes on outer mesophotic shelf environments has remained under described. Middleton Reef is a remote, high-latitude, oceanic platform reef that is located within a no-take area in the Lord Howe Marine Park off eastern Australia. Here we used baited remote underwater stereo video to sample predatory fishes across lagoon and outer shelf habitats from depths 0–100 m, extending knowledge on use of mesophotic depths and habitats. Many predatory fish demonstrated clear depth and habitat associations over this depth range. Carcharhinid sharks and Carangid fishes were the most abundant predators sampled on Middleton Reef, with five predatory fishes accounting for over 90% of the predator fish biomass. Notably, Galapagos shark ( Carcharhinus galapagensis ) and the protected black rockcod ( Epinephelus daemelii ) dominated the predator fish assemblage. A higher richness of predator fish species was sampled on reef areas north and south of the lagoon. The more exposed southern aspect of the reef supported a different suite of predator fish across mesophotic habitats relative to the assemblage recorded in the north and lagoonal habitats, a pattern potentially driven by differences in hard coral cover. Biomass of predatory fishes in the more sheltered north habitats was twice that of other areas, predominantly driven by high abundances of Galapagos shark. This work adds to the growing body of literature highlighting the conservation value of isolated oceanic reefs and the need to ensure that lagoon, shallow and mesophotic habitats in these systems are adequately protected, as they support vulnerable ecologically and economically important predator fish assemblages.
... Distorted production data can cause erroneous assessments of fishing mortality and stock status [13,14], leading to the ill-informed expansion of current global shark fisheries; this is mainly due to serious bycatch and the lack of publicity for shark protection policies. Because of limited and chaotic management policies [11,15,16], a lack of economic incentives, and limited data, current shark fishery management is inadequate [11,[17][18][19]. No formal fishery resource assessment exists for most cartilaginous fish in the world [20], and the IUCN Red List cites a square of cartilaginous species as threatened by overfishing, with only one-third of species regarded as safe [1], and 44% of species unable to be accurately assessed because of a lack of data. ...
Article
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Sharks occupy an important ecological niche in marine ecosystems. As top predators, they can restrict and control the behavior, numbers and composition of other species through downward effects, and play an essential role in ecosystem stability. Shark fishery data are limited, and for most Chondrichthyes species there is no formal fishery resource assessment at a global level. In this study, we applied the length-based Bayesian biomass (LBB) estimation method to assess the stock status of four common shark bycatch species of which more than 100 samples were collected in coastal waters of the northern South China Sea. Estimates of the length of 50% of individuals captured by gear/the length at first capture that maximized the catch and biomass (Lc/Lc_opt) of a species ranged from 0.49 to 1.4; the draughtsboard shark Cephaloscyllium sarawakensis had the highest value, and the shortnose dogfish Squalus brevirostris had the lowest. Estimates of the collected biomass/biomass of the maximum sustainable yield (B/BMSY) ranged from 0.86 to 1.9. Both C. sarawakensis and the spadenose shark Scoliodon laticaudus were fully exploited, while the spatulasnout catshark Apristurus platyrhynchus and S. brevirostris were in good condition. To verify the stability of the LBB, length frequency data for the most common species S. laticaudus were divided into different size-class intervals; simulations revealed estimated parameters based on these to be insensitive to differences in intervals, except for the smallest (10 mm), which did not affect evaluation results. These results can be used to provide a scientific basis on which shark fisheries in this region can be managed and prior parameters for related resource assessment methods can be determined.
... The extinction or decline of apex predator populations can cause ecosystem wide effects with direct impacts on other commercial fisheries. Furthermore, this can result in 'ripple effects' by enabling mesopredator populations to increase thus endangering the lower trophic levels they feed on (Ferretti et al., 2010;Travis et al., 2014). Several studies have indicated failures in wildlife conservation and management in areas classified as EBSAs due to overexploitation and lack of effective management (Pitcher, 2001;Dulvy, Sadovy & Reynolds, 2003). ...
Article
Ecologically or Biologically Significant Marine Areas (EBSAs) are rare, and highly important sites to the life history of a number of declining shark species are endangered by fishing. The high diversity of sharks caught by fisheries is difficult to monitor due to the scarcity of information on species-specific biological aspects (growth, maturity and fertility rate). There are two EBSAs off north-eastern Brazil, where key species are caught, more specifically the oceanic whitetip (Carcharhinus longimanus), mako (Isurus oxyrinchus), blue (Prionace glauca) and silky (Carcharhinus falciformis) sharks. Another 23 species displaying low frequency in catches have also been recorded, many of them considered threatened according to the IUCN Red List and the Brazilian Ministry of Environment. The main purpose of this study was to generate information about shark diversity and demonstrate the role of the two EBSAs in their conservation. After analysing fishing data collected from 2000 to 2011, maps were built to categorize shark species by phases of their ontogenetic development (neonate, young and adult) based on samples of C. falciformis (n = 330), C. longimanus (n = 440), I. oxyrinchus (n = 452) and P. glauca (n = 8,176). Shark stocks comprised mainly juveniles, which raises concerns since they are considered a crucial life stage for the sustainability of shark populations. Catch monitoring also highlighted that several of the species caught are threatened and their catch is either prohibited or limited according to the Brazilian laws and international rules in place. Action plans and enforcement of laws and rules are needed to deliver the protective measures needed for shark species in these EBSAs.
... The study of trophic relationships is particularly important in marine communities where sympatric species are ecologically interacting . Each species has an Responsible Editor: V.V.S.S. Sarma ecological role, and sharks particularly play significant roles as predators in regulating ecosystems functioning through both top-down and bottom-up effects with important consequences on the community Ferretti et al. 2010;Shipley et al. 2018). ...
Article
Sharks are top predators and play an important role in the regulation of marine ecosystems at lower trophic position. Mustelus californicus, Sphyrna zygaena, and Isurus oxyrinchus prove to be important fishery resources along the western coast of Baja California Sur and cohabit the same coastal areas, probably sharing resources. However, our knowledge about ecological dynamics of multiple species coexisting and sharing similar habitat resources is still limited, particularly for predators such as sharks. Therefore, this study focuses on the analysis of trophic ecology of the sharks species, using carbon (13C) and nitrogen (15N) stable isotope values in muscle tissues coupled with trace element concentration (Hg, Se, and Cd) in muscle and hepatic tissues of sharks. The values of δ13C (M. californicus -17.3 ± 1.1‰, S. zygaena -17.9 ± 0.5‰, and I. oxyrinchus -18.3 ± 0.3‰) and δ15N (M. californicus 18.2 ± 1.1‰, S. zygaena 18.4 ± 0.9‰, and I. oxyrinchus 17.8 ± 1.1‰) indicated that these species feed in the Gulf of Ulloa all throughout the year, and for extended periods with similar habitat use and trophic niche. The above-mentioned statement is also a conclusion supported by the significant correlation between isotopic and trace element concentrations in the muscular tissues in all studied species. Thus, the results of the present study emphasize the habitat and niche characteristics of three sympatric sharks off the coast of Baja California Sur, Mexico.
... Daging dan sirip hiu merupakan produk hiu yang paling banyak diminati konsumen; namun, produk hiu lainnya tidak dicatat secara terpisah dalam statistik perdagangan, sehingga sulit untuk dilacak. Hiu sangat rentan punah apabila mengalami penangkapan berlebih karena faktor biologis misalnya kematangan seksual yang lambat, periode kehamilan yang relatif lama, dan fekunditas yang rendah (Ferretti et al. 2010;Bräutigam et al. 2015). ...
Article
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Perikanan hiu dan pari di Indonesia, termasuk Tanjung Luar di NTB, menghadapi tantangan besar karena populasi hiu dan pari yang terus menurun. Hiu sangat rentan terhadap penangkapan berlebih dan kepunahan karena faktor seperti kematangan seksual yang lambat dan fekunditas yang rendah. Daging dan sirip hiu umunya diminati konsumen; namun, produk hiu lainnya tidak dicatat secara terpisah dalam statistik perdagangan, sehingga sulit untuk diidentifikasi berdasarkan indikator morfologi. Sebagai alternatifnya dapat menggunakan metode DNA barcoding. Penelitian ini bertujuan untuk mengidentifikasi spesies hiu langka yang terdaftar di CITES yang telah mendarat di pelabuhan NTB menggunakan metode DNA barcoding. Penelitian yang dilakukan meliputi tahap isolasi DNA, amplifikasi DNA, sekuensing dan analisis bioinformatika. Hasil sekuensing DNA dan analisis bioinformatika menunjukkan spesies Sphyrna lewini dan Carcharhinus falciformis teridentifikasi pada sampel dengan tingkat kemiripan 99-100%. Hasil ini menunjukkan ikan hiu yang termasuk dalam daftar CITES masih kerap ditangkap dan dimanfaatkan, sehingga perlu dilakukan regulasi yang lebih tegas dan transfer pengetahuan kepada masyarakat agar spesies hiu yang tergolong terancam punah dapat dilestarikan.
... Overfishing and habitat degradation have profoundly altered populations of marine animals (Hutchings, 2000;Lotze et al., 2006;Polidoro et al., 2012), especially sharks and rays (Stevens et al., 2000;Simpfendorfer et al., 2002;Dudley and Simpfendorfer, 2006;Ferretti et al., 2010). It is not clear, however, whether the population declines of globally distributed species are locally reversible or symptomatic of an erosion of resilience and chronic accumulation of global marine extinction risk (Jackson, 2010;Neubauer et al., 2013). ...
Article
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The rapid expansion of human activities threatens ocean-wide biodiversity. Numerous marine animal populations have declined, yet it remains unclear whether these trends are symptomatic of a chronic accumulation of global marine extinction risk. We present the first systematic analysis of threat for a globally distributed lineage of 1,041 chondrichthyan fishes-sharks, rays, and chimaeras. We estimate that one-quarter are threatened according to IUCN Red List criteria due to overfishing (targeted and incidental). Large-bodied, shallow-water species are at greatest risk and five out of the seven most threatened families are rays. Overall chondrichthyan extinction risk is substantially higher than for most other vertebrates, and only one-third of species are considered safe. Population depletion has occurred throughout the world's ice-free waters, but is particularly prevalent in the Indo-Pacific Biodiversity Triangle and Mediterranean Sea. Improved management of fisheries and trade is urgently needed to avoid extinctions and promote population recovery.
... This subclass includes sharks and batoids (superorder of cartilaginous flat-bodied fish consisting of skates, rays, and guitarfish) and encompasses over 1000 known living species (Weigmann, 2016). Almost all the aforementioned species are predatory and variations in their numbers may significantly affect marine ecosystems (Ferretti et al., 2010). Also, adding to their ecological relevance, they present a considerable societal relevance since sharks and rays represent a substantial source of revenue and food to many people around the World (Dent and Clarke, 2015). ...
Article
Bioindicator species are increasingly valuable in environmental pollution monitoring, and elasmobranch species include many suitable candidates for that role. By measuring contaminants and employing biomarkers of effect in relevant elasmobranch species, scientists may gain important insights about the impacts of pollution in marine ecosystems. This review compiles biomarkers applied in elasmobranchs to assess the effect of pollutants (e.g., metals, persistent organic pollutants, and plastics), and the environmental changes induced by anthropogenic activities (e.g., shifts in marine temperature, pH, and oxygenation). Over 30 biomarkers measured in more than 12 species were examined, including biotransformation biomarkers (e.g., cytochrome P450 1A), oxidative stress-related biomarkers (e.g., superoxide anion, lipid peroxidation, catalase, and vitamins), stress proteins (e.g., heat shock protein 70), reproductive and endocrine biomarkers (e.g., vitellogenin), osmoregulation biomarkers (e.g., trimethylamine N-oxide, Na⁺/K⁺-ATPase, and plasma ions), energetic and neurotoxic biomarkers (e.g., lactate dehydrogenase, lactate, and cholinesterases), and histopathological and morphologic biomarkers (e.g., tissue lesions and gross indices).
... Sharks are top-order predators that play important roles in the shallow water ecosystems of reefs, embayments and estuaries throughout tropical and temperate oceans by transferring energy and predation risk across seascapes [1][2][3][4][5] . The coasts bordering these shallow habitats are often centres of human population and activities, notably tourism, recreational and commercial fishing, and industrial development (ports, mining facilities etc.). ...
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.
... 1,2 The population of these species has been drastically reduced as they are targeted worldwide in the recent days. [3][4][5] This population decrease is due to the outcome of significant human activities such as overfishing, habitat destruction, slow reproduction, long gestation periods and low fecundity. 6 Species identification is important for population studies and stock management. ...
Article
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The morphological identification of certain species of shark and rays is very difficult. The mitogenome sequencing is noteworthy to solve the fish taxonomic uncertainties and phylogeny. The complete mitogenome of Mobula tarapacana (NCBI Accession No: MH669414) and Galeocerdo cuvier (NCBI Accession No: MH648005) were used to assess the phylogenetic and taxonomic status of these closely related species. Predominantly, the cytochrome oxidase I subunit (COI) was considered as a suitable marker gene for a species-level identification. The quality and quantity of the DNA were obtained by using spectrophotometric methods. The average mean value of electropherogram peak displayed the library fragments in M. tarapacana and G. cuvier with size ranging between 531 bp (M. tarapacana) and 546 bp (G. cuvier) respectively. The phylogenetic relationships between the closed related species were evaluated using the Maximum likelihood method.
... Elasmobranchs are considered one of the taxonomic groups with the greatest diversity. They have an important role in the control and regulation of other species populations, in addition to influencing the structure and function of coastal and oceanic ecosystems and being useful as indicators of the marine ecosystems health (Ferretti et al 2010). There are approximately 1402 elasmobranch species worldwide (594 sharks and 808 skates/rays) (Fricke et al 2021), of which 206 species (111 sharks and 95 skates/ rays) have been reported for Mexican waters, placing Mexico as the second most biodiverse country in terms of elasmobranch species after Australia (Del Moral-Flores et al 2015, Ehemann et al 2018. ...
Article
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The present study includes a list of elasmobranch species present in the Mexican Caribbean and the conservation status of each species with recommendations to improve the management strategies that are ongoing in the region. Since 2015, surveys were conducted in local fisheries, sighting reports were collected, and several published sources, including those from national and international collections and museums, were reviewed. Based on documents, collections, direct records by authors, and local sighting reports, we found 85 elasmobranch species (49 sharks and 36 rays) reported for the Mexican Caribbean, from which 65 species (37 sharks and 28 rays) have been confirmed. The present study increased the total number of elasmobranch species known to be in the Mexican Caribbean by 57. These species belong to 10 orders and 30 families. This represents 41% of the elasmobranch species known for Mexico and 47% of the species reported for the Wester Central Atlantic Ocean. This research provides important baseline information about elasmobranch biodiversity in the Mexican Caribbean with implications in the management and conservation of these species at national and international levels.
... Further, consideration should be taken of ecosystem importance, non-catch value, and constituent demand when determining stock assessment frequency (Methot, 2015). As higher trophic level predators (Cortés, 1999), large coastal sharks may have an ecosystem role as top-down predators and maintainers of ecosystem stability (Ferretti et al., 2010;. Further, large coastal sharks have proven particularly challenging to manage amongst conflicting stakeholder interests . ...
Thesis
Coastal sharks represent a group of stocks for which observation, assessment, and management are particularly challenging. Large distributional ranges, complex migratory behavior, low economic value, and relatively few observations in fishery independent surveys hinder relative abundance estimation. Assessing stock status of coastal sharks is encumbered by limited data availability, data quality, and knowledge of life history strategy. Further, coastal sharks are challenging to manage due to their slow intrinsic population growth rates, competing stakeholder interests, history of overexploitation, and in some cases, subjection to international exploitation. This dissertation aimed to improve the capacity to observe relative abundance of coastal sharks. Because a comprehensive survey is unavailable across the full distribution of coastal shark species in the southeast United States, several spatially-limited surveys are conducted, each assumed to represent an independent measure of relative abundance. When compiled, these indices of abundance regularly conflict, obscuring the true trend in stock abundance and potentially biasing estimates of stock status from stock assessments. Using age-structured simulations for Atlantic sharpnose and sandbar sharks, we tested whether dynamic factor analysis (DFA) is an appropriate statistical approach to reconcile conflicting survey indices. The resulting DFA trends were then input into a stock assessment model and results were compared to those generated from inputting conflicting indices into a corresponding assessment model. DFA proved useful in clarifying underlying patterns in stock abundance when the stock abundance exhibited sufficient contrast, and DFA trends were shown to produce more consistent (precise) assessment results. This dissertation serves to improve the capacity to observe patterns in relative abundance over time and likewise expand the toolbox for coastal shark stock assessments. Fishery management procedures (MPs) are pre-agreed upon frameworks designed to manage a stock and typically include information on how the stock is monitored, assessed, how stock status will alter management regulations (‘harvest control rule;’ HCR), and how the management regulations will be applied to the stock. No MP has been developed for coastal sharks in the United States. Consequently, we examined the impact of various HCR parameterizations and stock assessment frequency for the large coastal sandbar shark using a simulation approach termed management strategy evaluation. Notably, sandbar sharks are subjected to unregulated, international removals by Mexico, and the level of future Mexican removals was found to have a significant impact on the ability of the sandbar shark to recover. Trade-offs in management objectives with respect to various parameterizations of the harvest control rule were presented. Further, the frequency of stock assessments had a relatively small impact on the management objectives of the sandbar shark fishery. Through management strategy evaluation, international removals were identified as a potential barrier to sandbar shark recovery. Further, the vast resources required to undergo more numerous stock assessments could be potentially alleviated by reduction of future large coastal shark assessment frequency without compromising management success.
... Characteristics associated with high longevity, late maturity, slow growth rate, and low fecundity make this once abundant species experience severe population declines throughout its global range due to overfishing (D'Alberto et al., 2017;Myers et al., 2007;Ward & Myers, 2005). The decline of large predatory species was reported to reduce the natural mortality in a range of their preys and trigger trophic cascade changes in many marine ecosystems (Ferretti et al., 2010). Recently, the oceanic whitetip shark was listed as Critically Endangered by the International Union for the Conservation of Nature (IUCN), as well as being classified to Appendix II of the Convention on International Trade in Endangered Species (CITES) in 2013 (Rigby et al., 2019). ...
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There is a common phenomenon in nature whereby some animals have differences in their ontogenetic changes in dietary preferences between sexes, especially apex predators. These reflect changes in the needs of development during their lifetimes. Apex predators potentially have diverse dietary niches and a large impact on the trophic dynamics within ecosystems. However, the difference in life history between males and females often leads to increased difficulty in management and conservation. In this study, 25 oceanic whitetip sharks, Carcharhinus longimanus, were collected from the central and eastern tropical Pacific. Retrospective stable isotope analysis of vertebrae was used to evaluate the potential ontogenetic differences in feeding habits and niche width between sexes. Results showed that C. longimanus had a wide range of δ¹³C values (−18.1 to −12.3‰) and δ¹⁵N values (8.9–14.8‰). However, males and females had similar trophic positions with large niche overlap at similar growth stages. Both sexes had increasing δ¹³C values but relatively constant δ¹⁵N values along the vertebrae. These results indicated that male and female C. longimanus may share similar feeding strategies and movement patterns. The results presented in this study enhance our understanding of sexual ontogenetic patterns and ecological role of C. longimanus and highlighted the applicability of vertebrae for characterizing shark life-history traits.
... Sharks, rays and chimaeras, collectively called chondrichthyans, provide valuable contributions to people, through direct economic benefits from the fisheries and tourism industries, as important food sources in many parts of the world, and by playing critical ecological roles in aquatic ecosystems (Ferretti et al., 2010;Gallagher and Hammerschlag, 2011;WWF, 2021). However, chondrichthyans are one of the most threatened groups in the world, with over a third of all known species currently threatened with extinction due to overfishing and other anthropogenic activities (IUCN, 2021). ...
Article
With global biodiversity currently facing unprecedented losses, it is critical that resources are allocated and used effectively to mitigate these threats, especially in resource-limited tropical countries of the global south. Chondrichthyans (sharks, rays and chimaeras) are particularly threatened by overexploitation, with India being amongst the top fishing nations for these species and a priority region for their conservation. We conducted a scoping review of chondrichthyan literature in India to assess the relevance of this research to the conservation of these threatened species. Between March and April 2021, we searched for peer reviewed and grey literature across national and international databases and found 482 chondrichthyan publications. While the number of publications exponentially increased with time, the literature is dominated by short-term fisheries studies, biological records and observations, with less than 10% of studies addressing socio-economic and management themes. Research was biased towards specific states, particularly Tamil Nadu and Kerala, and towards charismatic species like the whale shark, leading to under-representation of potentially important regions and taxa. Overall, our study found low relevance and applicability of India's research literature to chondrichthyan conservation. There is a need for more directed and applied research explicitly aimed at informing conservation. We highlight specific data gaps, such as the need for improved understanding of the socio-economic aspects of chondrichthyan fisheries, species risk assessments at the regional level, data on critical habitats, and the evaluation of existing policies. Addressing these gaps can help ensure that effort is allocated to the regions, species and topics that need it the most, for improved conservation outcomes.
... The most threatened species are predominately largebodied species in shallow, coastal areas (Dulvy et al., 2014). The decline of these species-especially those that are important predators-has potentially serious consequences for ecosystem structure, function and services (Stevens et al., 2000;Baum & Worm, 2009;Ferretti et al., 2010). Consequently, there is an urgent need for research into the efficacy of management approaches designed to reduce the pressures on these species. ...
Article
• Marine Protected Areas (MPAs) are widely used in marine management, but for mobile species understanding the spatio-temporal scale of management measures that is required to deliver conservation benefits depends on a detailed knowledge of species’ movements that is often lacking. This is especially the case for species of skate (Rajidae) for which relatively few movement studies have been conducted. • In Scotland, the Loch Sunart to the Sound of Jura MPA covering 741 km² has been designated for the conservation of the Critically Endangered flapper skate (Dipturus intermedius), but fine-scale movements within this area remain poorly understood. • A passive acoustic telemetry study which coupled acoustic tagging of 42 individuals and a static array of 58 receivers was conducted from March 2016 to June 2017. Using acoustic detection time series, angler capture–recapture data and depth time series from archival tags, fine-scale movements of individuals were investigated. • Overall, 33 of the 42 tagged individuals were detected. Residency, site fidelity and transiency were documented. Residency around receivers, lasting from 3 to more than 12 months, was documented in 16 acoustically detected individuals (48%) and all life-history categories, but was most noticeable among females. Acoustic detections were associated with depth, salinity and season, but there was no evidence that individuals formed close-knit groups in the areas in which they were detected. • Taken together with historical occurrence records of flapper skate, the prevalence and scale of residency documented here suggest that the MPA is sufficiently large to benefit a notable percentage (38 [24–52]%) of skate found in the study area over monthly and seasonal timescales. This result strengthens the case for the use of MPAs to support the conservation of flapper skate and other skate species that display similar movement patterns in areas of high local abundance.
... While the expanding Mediterranean fisheries in deeper waters (Celona et al. 2005, Ferretti et al. 2008, Kabasakal 2013) may have contributed to a large number of sightings in the last 2 decades, its continued impact on the population may have eventually eroded any compensatory population response to changing interspecific interactions, as suggested by the recent significant decline in relative sighting rate (Fig. 2). Similar compensatory population increases eventually damped down by the effect of intensive exploitation have been demonstrated in other ocean sectors (Baum & Worm 2009, Ferretti et al. 2010. ...
Article
In the last 50 yr, shark populations showed steep declines in the Mediterranean Sea. The IUCN lists most Mediterranean species as Endangered (55%), while considering 27.5% of them Data Deficient. Here, sharks are currently one of the rarest and more elusive groups of animals, and data from fisheries and scientific monitoring still insufficiently support robust abundance and distribution assessments. New technologies can fill this data gap by linking people and scientists through new monitoring strategies. SharkPulse, an international collaborative project, aims at creating a large world database of shark occurrence records by mining images on the web, social networks, and private archives. Here we analyzed 1186 sharkPulse records from the Mediterranean Sea. We collected records to characterize spatio-temporal patterns on 37 species, highlighting distribution changes for 5, and, by using generalized linear models, estimating trends in sighting for the most abundant species. With 273 records, Hexanchus griseus had the most sighting records since the beginning of the series. We identified pupping areas and aggregation sites for immature Prionace glauca and Isurus oxyrinchus; pinpointed strongholds of the Critically Endangered Squatina squatina to focus conservation efforts; and identified broader than previously reported regional distribution ranges for Alopias superciliosus, Dalatias licha, Heptranchias perlo, H. griseus, Oxynotus centrina, and P. glauca. We confirmed that fishing is still the major threat for Mediterranean sharks and call for a greater effort in controlling the emerging patterns with efficient conservation effort indexes. If properly standardized, opportunistic data can efficiently and cost-effectively advance our understanding of shark abundance, distribution, and conservation status.
... Similarly, killer whale (Orcinus orca) presence alters space use of white sharks (Carcharodon carcharias) at elephant seal (Mirounga angustirostrous) haul-out sites, redistributing predation pressure and risk on seal colonies (Jorgensen et al., 2019). With many apex and mesopredator populations in decline, their loss may result in long-lasting ecosystem-wide shifts, including trophic cascades (Crooks & Soulé, 1999;Estes et al., 2011;Estes et al., 2016;Ferretti et al., 2010;Heithaus, Frid, et al., 2008;Heupel et al., 2014;Nowicki et al., 2021;Ripple et al., 2016). ...
Article
Interspecific interactions can play an essential role in shaping wildlife populations and communities. To date, assessments of interspecific interactions, and more specifically predator–prey dynamics, in aquatic systems over broad spatial and temporal scales (i.e., hundreds of km and multiple years) are rare due to constraints on our abilities to measure effectively at those scales. We applied new methods to identify space use overlap and potential predation risk to Atlantic tarpon (Megalops atlanticus) and permit (Trachinotus falcatus) from two known predators, great hammerhead (Sphyrna mokarran) and bull (Carcharhinus leucas) sharks over a three year period using acoustic telemetry in the coastal region of the Florida Keys (USA). By examining spatial‐temporal overlap, as well as the timing and order of arrival at specific locations compared to random chance, we show that potential predation risk from great hammerhead and bull sharks to Atlantic tarpon and permit are heterogeneous across the Florida Keys. Additionally, we found that predator encounter rates with these game fishes are elevated at specific locations and times, including a pre‐spawning aggregation site in the case of Atlantic tarpon. Further, using machine learning algorithms, we identify environmental variability in overlap between predators and their potential prey, including location, habitat, time of year, lunar cycle, depth, and water temperature. These predator–prey landscapes provide insights into fundamental ecosystem function and biological conservation, especially in the context of emerging fisheries‐related depredation issues in coastal marine ecosystems.
... Shark declines can have strong ecological consequences. Except in coral reef ecosystems (Desbiens et al., 2021), the absence of sharks can indirectly alter predation pressure on different fish species via behavioral responses of meso-consumers released from predator intimidation (Frid et al., 2008), altering the total fish assemblage through trophic interactions and shaping marine communities over large spatial and temporal scales (Stevens et al., 2000;Ferretti et al., 2010). The manner in which sharks structure communities may also be shifting with climate change, where the recent increase of seawater temperatures has been linked to a poleward shift in shark distributions (Dolgov et al., 2005;Tanaka et al., 2021) and a potential reduction of dive depths due to increased deoxygenation (Vedor et al., 2021b). ...
Article
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Blue shark (Prionace glauca) is amongst the most abundant shark species in international trade, however this highly migratory species has little effective management and the need for spatio-temporal strategies increases, possibly involving the most vulnerable stage or sex classes. We combined 265,595 blue shark observations (capture or satellite tag) with environmental data to present the first global-scale analysis of species’ habitat preferences for five size and sex classes (small juveniles, large juvenile males and females, adult males and females). We leveraged the understanding of blue shark biotic environmental associations to develop two indicators of foraging location: productivity fronts in mesotrophic areas and mesopelagic micronekton in oligotrophic environments. Temperature (at surface and mixed layer depth plus 100 m) and sea surface height anomaly were used to exclude unsuitable abiotic environments. To capture the horizontal and vertical extent of thermal habitat for the blue shark, we defined the temperature niche relative to both sea surface temperature (SST) and the temperature 100 m below the mixed layer depth (Tmld+100). We show that the lifetime foraging niche incorporates highly diverse biotic and abiotic conditions: the blue shark tends to shift from mesotrophic and temperate surface waters during juvenile stages to more oligotrophic and warm surface waters for adults. However, low productivity limits all classes of blue shark habitat in the tropical western North Atlantic, and both low productivity and warm temperatures limit habitat in most of the equatorial Indian Ocean (except for the adult males) and tropical eastern Pacific. Large females tend to have greater habitat overlap with small juveniles than large males, more defined by temperature than productivity preferences. In particular, large juvenile females tend to extend their range into higher latitudes than large males, likely due to greater tolerance to relatively cold waters. Large juvenile and adult females also seem to avoid areas with intermediate SST (~21.7-24.0°C), resulting in separation from large males mostly in the tropical and temperate latitudes in the cold and warm seasons, respectively. The habitat requirements of sensitive size- and sex-specific stages to blue shark population dynamics are essential in management to improve conservation of this near-threatened species.
... Their k-strategy life history traits (e.g., low fertility, slow growth and late maturity) limit their capacity to increase and maintain a viable population in the face of anthropogenic pressures (Cailliet et al., 2005;Elliott et al., 2020a). Overfishing and bycatch are considered as the main factors for their decline, and one in four elasmobranch species are threatened with extinction at global scale (Ferretti et al., 2010;Dulvy et al., 2014). 39% of elasmobranch species are considered as Data Deficient (DD) by the International Union for Conservation of Nature (IUCN), given the lack of information on their distribution and populations structures (IUCN, 2020). ...
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.
... One of the most substantial conflicts occurs due to some fishers calling for sharks to be culled and/or commercial shark fisheries to be expanded (Mercer, 2015;Kagi, 2016), which some stakeholders supporting shark conservation are against. Awareness of shark conservation has increased substantially in recent decades due to research documenting the plight of sharks, with some species reported to have declined by as much as 95% (Robbins et al., 2006;Ferretti et al., 2010;Pacoureau et al., 2021), as well as high-profile documentaries such as 'SharkWater' exposing the global threat to sharks from international trade. This increase in shark conservation messaging has likely led to reduced marketability of sharks in Australia, as highlighted by some major supermarkets no longer selling shark products over the last 10-20 years. ...
... Elasmobranchs provide services to marine ecosystems that are of incommensurable value (Tavares et al., 2019), but their populations have declined substantially over the last 50 years (Davidson et al., 2016;Roff et al., 2018), mainly due to overfishing (Stevens et al., 2000) and increased market demand for shark products (Dent & Clarke, 2015). This decline may cause unpredictable cascade effects on marine trophic webs (Casini et al., 2009;Ferretti et al., 2010;Bornatowski et al., 2014) and human activities that rely on sharks (Britten et al., 2014). Eighty-eight chondrichthyan (sharks, rays, and chimaeras) species are found in the Mediterranean Sea (Serena et al., 2020), of which, 53% of the species assessed by the International Union for Conservation of Nature (IUCN) are considered at risk of extinction Otero et al., 2019), with an additional 18% classified as Data Deficient . ...
Article
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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.
... Given the general K-selected life history of most shark species (i.e., late maturing, low fecundity, and long-lives, Cortés, 2000), they are particularly vulnerable to overexploitation and recovery can be protracted over long time spans (Peterson et al., 2017). The loss of large, apex predators has led to concern about resulting ecosystem imbalances (Ferretti et al., 2010). However, the implications from the decline of top predatory sharks are still uncertain, as these are complex ecological and trophic relationships, which likely vary across species, habitats, and regions (Estes et al., 2016;Grubbs et al., 2016). ...
Article
Abundances of large sharks are reported to have declined worldwide, and in response various levels of fisheries management and conservation efforts have been established. For example, Marine Protected Areas have been suggested as means to protect large expanses of ocean from fishing and other industrial activities (e.g., habitat destruction), and in 2011 The Commonwealth of The Bahamas established The Bahamas Shark Sanctuary. However, assessing the effectiveness of conservation efforts is challenging because consistent long‐term datasets of shark abundances are often lacking, especially throughout the Caribbean and The Bahamas. Here, we investigated the catch rates and demographics of tiger sharks Galeocerdo cuvier caught in a fishery‐independent survey near Bimini, The Bahamas, from 1984 to 2019 to assess relative abundance trends following the banning of longline fishing in 1993 and the subsequent establishment of the shark sanctuary. To contextualize the relative abundance trends near Bimini, we compared this to the relative abundance of tiger sharks in a fishery‐dependent survey from the Southeastern USA (SE USA), conducted from 1994 to 2019. Our data suggest that local abundance of tiger sharks has been stable near Bimini since the 1980s, including after the banning of longline fishing and the implementation of the shark sanctuary. In comparison, the abundance near the SE USA has slowly increased in the last decade, following potential declines in the decade preceding the USA Shark Management Plan. The results of this study provide some optimism that current conservation efforts in The Bahamas have been effective to maintain local tiger shark abundance within the protected area. Additionally, current fisheries management in the SE USA is allowing this species to recover within those waters. This article is protected by copyright. All rights reserved.
... In particular, elasmobranchs (sharks, rays and skates) are keystone species in many ecosystems in which they fill several roles in food chains as top-and meso-predators [17,18], and declines in elasmobranch populations can have dramatic effects on ecosystem function [19]. While large sharks have received increased attention due to their prominent role as top predators [20][21][22][23], mesopredators, such as rays, are far less studied. ...
Article
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Background Animal-associated microbiomes can be influenced by both host and environmental factors. Comparing wild animals to those in zoos or aquariums can help disentangle the effects of host versus environmental factors, while also testing whether managed conditions foster a ‘natural’ host microbiome. Focusing on an endangered elasmobranch species—the whitespotted eagle ray Aetobatus narinari—we compared the skin, gill, and cloaca microbiomes of wild individuals to those at Georgia Aquarium. Whitespotted eagle ray microbiomes from Georgia Aquarium were also compared to those of cownose rays (Rhinoptera bonasus) in the same exhibit, allowing us to explore the effect of host identity on the ray microbiome. Results Long-term veterinary monitoring indicated that the rays in managed care did not have a history of disease and maintained health parameters consistent with those of wild individuals, with one exception. Aquarium whitespotted eagle rays were regularly treated to control parasite loads, but the effects on animal health were subclinical. Microbiome α- and β-diversity differed between wild versus aquarium whitespotted eagle rays at all body sites, with α-diversity significantly higher in wild individuals. β-diversity differences in wild versus aquarium whitespotted eagle rays were greater for skin and gill microbiomes compared to those of the cloaca. At each body site, we also detected microbial taxa shared between wild and aquarium eagle rays. Additionally, the cloaca, skin, and gill microbiomes of aquarium eagle rays differed from those of cownose rays in the same exhibit. Potentially pathogenic bacteria were at low abundance in all wild and aquarium rays. Conclusion For whitespotted eagle rays, managed care was associated with a microbiome differing significantly from that of wild individuals. These differences were not absolute, as the microbiome of aquarium rays shared members with that of wild counterparts and was distinct from that of a cohabitating ray species. Eagle rays under managed care appear healthy, suggesting that their microbiomes are not associated with compromised host health. However, the ray microbiome is dynamic, differing with both environmental factors and host identity. Monitoring of aquarium ray microbiomes over time may identify taxonomic patterns that co-vary with host health.
... This group of sharks is also prized in the shark fin industry and typically have high mortality rates when caught as bycatch in longline fisheries [18]. As a result, hammerhead sharks have experienced dramatic population reductions worldwide [9, 16,19]. In some areas where they were historically abundant, research has demonstrated that hammerhead sharks have been overharvested and even extirpated (e.g., [24]). ...
Article
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Background The Northwestern Pacific is a data-poor region for studies into the movements and habitat use of open ocean and pelagic sharks. However, this region experiences considerable pressure from commercial fishing. Therefore, shark movement data from this region carry significant implications for conservation and management, particularly for threatened species. Here, we provide the first data on seasonal residency and movements of scalloped hammerhead ( Sphyrna lewini ) and Galapagos sharks ( Carcharhinus galapagensis) , using acoustic and satellite telemetry, and dive logbooks, off Japan. Results Eight female sharks, four of each species, were tagged around a coastal seamount off southeastern Japan (Mikomoto Island) in August 2015, and monitored for a period of up to 363 days using an array of six receivers around the island. Analyses of the more abundant scalloped hammerhead acoustic data suggest high seasonal residency predominantly from August to November associated with lower chlorophyll- a concentrations, before sharks then leave the island and return the following summer. Residency for scalloped hammerhead sharks were highest among those receivers closest to the Kuroshio Current, which produces strong coastal upwelling, however SST was not found to be predictive of occurrence at Mikomoto. Shark presence was corroborated by analysis of dive-log data from a local ecotourism operator. We also produced two unique satellite tracks, whereby a scalloped hammerhead exhibited a 200-km dispersal into a coastal embayment west of the tagging location and a Galapagos shark migrated over 800 km offshore into the high seas. Conclusion This study provided some of the first behavioral and movement data for scalloped hammerhead and Galapagos sharks in Japan. Our findings suggest varying spatial and temporal visitation of two shark species to a coastal seamount, underscored by some degree of seasonal residency and site fidelity and linked, for scalloped hammerhead sharks at least, to varying productivity. Furthermore, we provided preliminary evidence for long-distance dispersal of these species, and some site fidelity to seamounts in the region. This study highlights the importance of describing shark movements to aid in filling critical data gaps for poorly understood, endemic populations of threatened species.
... Open ocean habitats and species protection is complicated by the system's dynamic nature and the difficulty of delineating specific pelagic habitats, as well as questions of governance and international jurisdiction. However, protection of pelagic species like tuna, billfishes, marine mammals, and turtles is crucial, as many play important ecological roles for ecosystem structure and functioning (Myers et al., 2007;Heithaus et al., 2008;Ferretti et al., 2010;Silber et al., 2017;Bornatowski et al., 2018). Deep sea habitats are also data-poor and poorly protected in most ecoregions (Morato et al., 2010;Clark et al., 2012;Kennedy et al., 2019). ...
Article
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Marine protected areas (MPAs) are a key tool for achieving goals for biodiversity conservation and human well-being, including improving climate resilience and equitable access to nature. At a national level, they are central components in the U.S. commitment to conserve at least 30% of U.S. waters by 2030. By definition, the primary goal of an MPA is the long-term conservation of nature; however, not all MPAs provide the same ecological and social benefits. A U.S. system of MPAs that is equitable, well-managed, representative and connected, and includes areas at a level of protection that can deliver desired outcomes is best positioned to support national goals. We used a new MPA framework, The MPA Guide, to assess the level of protection and stage of establishment of the 50 largest U.S. MPAs, which make up 99.7% of the total U.S. MPA area (3.19 million km2). Over 96% of this area, including 99% of that which is fully or highly protected against extractive or destructive human activities, is in the central Pacific ocean. Total MPA area in other regions is sparse – only 1.9% of the U.S. ocean excluding the central Pacific is protected in any kind of MPA (120,976 km2). Over three quarters of the non-central Pacific MPA area is lightly or minimally protected against extractive or destructive human activities. These results highlight an urgent need to improve the quality, quantity, and representativeness of MPA protection in U.S. waters to bring benefits to human and marine communities. We identify and review the state of the science, including focal areas for achieving desired MPA outcomes and lessons learned from places where sound ecological and social design principles come together in MPAs that are set up to achieve national goals for equity, climate resilience, and biodiversity conservation. We recommend key opportunities for action specific to the U.S. context, including increasing funding, research, equity, and protection level for new and existing U.S. MPAs.
... While the expanding Mediterranean fisheries in deeper waters (Celona et al. 2005, Ferretti et al. 2008, Kabasakal 2013) may have contributed to a large number of sightings in the last 2 decades, its continued impact on the population may have eventually eroded any compensatory population response to changing interspecific interactions, as suggested by the recent significant decline in relative sighting rate (Fig. 2). Similar compensatory population increases eventually damped down by the effect of intensive exploitation have been demonstrated in other ocean sectors (Baum & Worm 2009, Ferretti et al. 2010. ...
... The depletion of shark and ray populations could lead to ecosystemlevel consequences (Burkholder et al., 2013;Estes et al., 2016;Ferretti et al., 2010) because many of these fishes are apex or mesopredators that range widely and may affect ecosystem processes through predation and associated risk effects, competition, nutrient transport and bioturbation Heithaus et al., 2008Heithaus et al., , 2010Heupel et al., 2014). ...
Article
Chondrichthyan fishes are among the most threatened vertebrates on the planet because many species have slow life histories that are outpaced by intense fishing. The Western Central Atlantic Ocean, which includes the Greater Caribbean, is a hotspot of chondrichthyan biodiversity and abundance, but has been characterized by extensive shark and ray fisheries and a lack of sufficient data for effective management and conservation. To inform future research and management decisions, we analysed patterns in chondrichthyan extinction risk, reconstructed catches and management engagement in this region. We summarized the extinction risk of 180 sharks, rays and chimaeras, including 66 endemic and 14 near‐endemic species, using contemporary IUCN Red List assessments. Over one‐third (35.6%) were assessed as Vulnerable, Endangered or Critically Endangered, primarily due to overfishing. Reconstructed catches from 1950 to 2016 peaked in 1992, then declined by 40.2% thereafter. The United States, Venezuela and Mexico were responsible for most catches in the region and hosted the largest proportions of the regional distributions of threatened species, largely due to having extensive coastal habitats in their Exclusive Economic Zones. The quantity and taxonomic resolution of fisheries landings data were poor in much of the region, and national‐level regulations varied widely across jurisdictions. Deepwater fisheries represent an emerging threat, although many deepwater chondrichthyans currently have refuge beyond the depths of most fisheries. Regional collaboration as well as effective and enforceable management informed by more complete fisheries data, particularly from small‐scale fisheries, are required to protect and recover threatened species and ensure sustainable fisheries.
... Elasmobranchs from coastal, reef-associated, and open ocean ecosystems have significantly declined over the last decades (Dulvy et al., 2008;Ferretti et al., 2010;MacNeil et al., 2020;Pacoureau et al., 2021). Despite conservation and management efforts in multiple regions around the world (including bans on shark finning, the regulation of the shark fin trade, and the establishment of marine protected areas), elasmobranch by-catch and exploitation are likely to remain at unsustainable levels at the global scale (Worm et al., 2013;Ward-Paige & Worm, 2017;MacKeracher, Diedrich & Simpfendorfer, 2019). ...
Article
Artisanal fisheries are socially and economically important along the Caribbean coast of Colombia. These fisheries remain poorly characterized, making it difficult to estimate their potential impact, especially on non‐targeted catch such as elasmobranchs. A rapid assessment framework was used to investigate the exploitation, use, and relative abundance of elasmobranchs and predatory teleosts in a region along the Caribbean coast of Colombia. In‐person structured interview surveys (n = 188) were conducted during the autumn of 2016 at eight fishing towns around Cartagena and the islands of the Natural National Park (NNP) Corales del Rosario and San Bernardo. Baited remote underwater video systems (BRUVS) (n = 200) deployed at four reefs were used to assess the relative abundance of elasmobranchs and other predatory teleosts. Fishers reported capturing eight shark and five ray taxa. Although 99% of fishers indicated that they did not target sharks, 83% reported keeping the catches to sell, eat, or both. Similarly, 81% of fishers did not target rays, but 90% reported retaining catches. Most fishers (84%) perceived a decline of sharks in the coastal waters since they started fishing, compared with 41% reporting batoid declines. BRUVS data support the perceptions of elasmobranch declines. Elasmobranch abundances were very low and no difference was detected between protected and unprotected reefs. Results were similar for teleost taxa, but there were higher abundances inside one marine protected area (MPA) that had high enforcement. Taken together, the data suggest considerable degradation of not only elasmobranch populations but also predatory fish populations of coral reef habitats in a region of the Colombian Caribbean. Furthermore, artisanal fishers continue to exploit coral reef resources inside MPAs unless there is strong enforcement. Enforcement can be difficult with limited resources, and therefore community‐based conservation methods may be more effective. Engagement with the local fishing community may help to reduce existing tensions and improve compliance.
... The lucrative nature of chondrichthyan fisheries have spurred the development of targeted commercial fisheries in many countries but large fractions of the total output are as a result of incidental capture or bycatch (Bradai et al., 2018). While sharks play important roles in maintaining productive and functional marine ecosystems (Ferretti et al., 2010), the increasing human demands for shark fins and meat and the decline of many marine fish stocks have caused shifts towards the targeted capture of these large pelagic species (Eriksson and Clarke, 2015) providing a crucial food source and income for several coastal communities (Christensen and Jackson, ). This has transformed the outlook of many hitherto, smallscale shark fisheries into active commercial fisheries fueled by the controversial practice of shark finning (Fowler et al., 2010). ...
Article
The decline in traditionally valuable fish stocks, coupled with an increased demand for shark fins and meat has caused many fishermen to target sharks. However, there is limited information on the fishing practices, gears, and catch distribution for the shark fisheries. This study used a semi-structured interview to characterize the shark fisheries and techniques used to catch sharks as well as the catch statistics and trade in fifteen coastal communities along the Eastern, Central, and Western coasts of Ghana. Out of the 470 fishers interviewed, 46% were specialized shark fishers while the remaining 54% landed sharks as bycatch. Specialized shark fishers captured between 7–10 individual sharks per fishing trip while by-catch shark fishers captured between 1–5 sharks. The shark species harvested include the blue shark, thresher shark, common and sand tiger, bull shark, short and longfin mako shark, hammerhead, and milk shark. Fishers along the eastern coast mostly capture sharks as bycatch, while those along the central and western coast of Ghana target sharks with specialized fishing gears. The catch data obtained from the fishers indicated higher shark landings and was linked to the development of longlines and drift gill nets with hooks attached to the footrope that target sharks, and are usually deployed along the western coastlines of Ghana. Nearly all the shark species captured in the study communities were listed by the IUCN as either “Endangered”, “Critically Endangered” or “Vulnerable”. Among fishers who target sharks, 74% stated that shark populations were declining and were spending more effort to capture the fish. Specialized shark fishers indicated a poor perception and attitude towards shark conservation along the entire coastline of the country and are not in support of shark conservation. It is recommended that the capture and trade in these species should be closely monitored to prevent the extinction of vulnerable populations.
... Although sharks provide several key ecological and economic benefits (Cisneros-Montemayor et al., 2013;Ruppert et al., 2013), they suffer from overexploitation and persecution globally (Friedrich, Jefferson & Glegg, 2014;Pacoureau et al., 2021). As an apex predator, sharks structure food webs both directly by regulating prey dynamics and indirectly by modifying prey behavior (Ferretti et al., 2010). Thus, the removal of sharks can result in altered ecosystem functioning and shifted food web dynamics (Heithaus et al., 2008). ...
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Sharks are often depicted in the media as violent killers that actively seek out opportunities to harm humans. This framing may impact human tolerance and support of shark conservation, underscoring the need to identify strategies that counteract these negative representations. Social media, given its widespread use, could be an effective platform for shaping public tolerance for sharks and other wildlife species. In this experimental study, we conducted an online pre‐post survey in Spring 2020 to determine how viewing shark‐related YouTube videos impacted tolerance for sharks among residents (n = 335) in the coastal state of North Carolina (NC), USA and neighboring states. The study employed framing theory, which suggests that the ways in which information is presented influence how it is processed and the actions that result from it. Participants were randomly assigned to one of two video treatments where sharks were framed positively or negatively. Each video treatment impacted tolerance for sharks in the direction of their framing: positive framing influenced positive changes in tolerance (70% more positive attitudes toward sharks, a 130% increase in acceptance of sharks and a 46% increase in intended shark conservation behaviors), and negative framing influenced negative changes (25% more negative attitudes toward sharks, a 18% decrease in acceptance of sharks and a 3% decrease in intended shark conservation behaviors). These findings suggest positive messages about sharks on social media promote tolerance of sharks and can be more impactful than negative messages. At least one form of social media, YouTube, appears to be a valuable tool for encouraging tolerance for sharks. Differences in change in attitudes, change in acceptance, and change in intended behaviors toward sharks between the positive shark video and negative shark video treatment groups. Change in each variable was calculated by subtracting the pre‐test score from the post‐test score for each variable. Significance levels: *P < 0.05, **P < 0.01, ***P < 0.001 for Welch’s t‐test comparing magnitude of change between the negative and positive treatments, adjusted with the Bonferroni correction for multiple comparisons. Error bars represent 95% confidence intervals. The dashed line represents a baseline of no change.
... For example, sharks and their relatives are expected to lose coverage under the current set of large marine protected areas (Davies et al. 2017). Likewise, shifts in distribution patterns and range retractions may impact the revenue obtained through fsheries and tourism directly, given this group's economic value (Gallagher and Hammerschlag 2011;Hammerschlag et al., 2019;Kendrick et al. 2019), and indirectly, given their potential to modulate community response through top-down pressure (Estes et al. 2016;Ferretti et al. 2010;Heithaus et al. 2010;Nowicki et al. 2019Nowicki et al. , 2021Wild et al. 2019; see also Chapter 15). On the other hand, climate change may also potentiate negative interactions with humans, as species historically perceived as "dangerous" move into new areas (Bangley et al. 2018;Chapman and McPhee 2016). ...
... With this spatial structure, our seafood markets make us operate as highly mobile consumers at the global scale, forming a generalist-like food web module that parallels nature's food webs (Fig. 1) with the potential to strongly impact marine and freshwater ecosystems. Importantly, the historical apex predators in these ecosystems are in precipitous decline due at least in part to anthropogenic stressors, reducing these ecosystems' inherent stabilizing capacity (Ferretti et al., 2010;Worm et al., 2013). ...
Article
Global fisheries and seafood supply chains have remarkable structural similarities to nature's food webs, with humans as apex predators, allowing us to use ecological concepts to draw connections between fisheries management and the stability and resilience of the global seafood system. However, misinformation currently plagues the global seafood market and may be preventing food webs' natural stabilizing features from working properly in the seafood system. We argue that misinformation blocks transparency throughout the entire supply chain and prevents consumers from making informed and potentially stabilizing decisions, undermining the sustainability of the global seafood system. Here, we first describe how food webs contain a remarkably repeated generalist module, characterized by flexible mobile generalist predators that adapt to resource variability in space by making rapid and “informed” foraging switches. Next, we discuss how the global seafood system mimics this structure but opposes the common stabilizing mechanism of nature's food webs because it is replete with misinformation. We conclude that modern tools combined with proper labelling can help create high information markets that allow consumers to make rapid and informed decisions. Predators' roles in nature's food webs indicate that smart switches in consumer foraging (i.e., demand) are critical for global seafood sustainability and the maintenance of marine biodiversity.
... Shark declines can have strong ecological consequences. Except in coral reef ecosystems (Desbiens et al., 2021), the absence of sharks can indirectly alter predation pressure on different fish species via behavioral responses of meso-consumers released from predator intimidation (Frid et al., 2008), altering the total fish assemblage through trophic interactions and shaping marine communities over large spatial and temporal scales (Stevens et al., 2000;Ferretti et al., 2010). The manner in which sharks structure communities may also be shifting with climate change, where the recent increase of seawater temperatures has been linked to a poleward shift in shark distributions (Dolgov et al., 2005;Tanaka et al., 2021) and a potential reduction of dive depths due to increased deoxygenation (Vedor et al., 2021b). ...
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Bigeye tuna (Thunnus obesus) and Yellowfin tuna (Thunnus albacares) are a marine commodity that has high nutritional content and economic value in the market. However, based on data from Palabuhanratu Archipelago Fishing Port, there has been a high decrease in the catch of Bigeye tuna and Yellowfin tuna since 2016 although slightly increased in the following year, so it is necessary to analyze the size trends of them as a target fish of many fishermen at the port. The purpose of this study is to determine the size trend of Bigeye and Yellowfin tuna for the next few years and to determine the steps to maintain their sustainability. The method used in this research is a case study and analyzed using regression analysis. The results showed that the size trend of Bigeye tuna and Yellowfin tuna catch until 2022 will tend to decline. This indicates the occurrence of overfishing so that it does not provide opportunities for fish to grow and develop. Therefore, catch control efforts are needed to maintain the sustainability of fish stocks.
Article
Given the global collapse of most oyster fisheries, we explored the conditions under which the interaction of oysters and fishers can lead to multiple system equilibria, and how those conditions might affect management strategies and recovery efforts. Using simple, but plausible, models of oyster fisheries, we identified tipping points, multiple equilibria, and hysteresis under a wide range of realistic model parameterizations. In collapsed systems with hysteresis, recovery of the system will require far less harvest than that which precipitated the collapse, and recovery times can be on decadal scales. We also derived optimal, non-equilibrium, state-dependent fishing policies and found that these policies can perform well, but are accompanied by high variation in the allowable harvest. Critically, these optimal policies also require constant monitoring of system state and frequent control of fishing effort. Finally, we examined habitat-enhancement scenarios that mimic proposed and ongoing restoration programs. We found that these efforts can increase the number of fishers the system can support and reduce otherwise long recovery times in collapsed systems.
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Pelagic elasmobranchs are key elements of oceanic ecosystems and must be preserved if marine trophic networks are to be kept in balance. Yet, they face intense fishing pressure that has been threatening their populations worldwide. Ensuring proper conservation management of these taxa depends on a better understanding of the strategies they use to explore the pelagic realm and their contributions to trophic web structuring across the ocean column. This study aimed at examining relationships between vertical habitat use and trophic attributes among six sympatric pelagic elasmobranchs using satellite transmitting tags in the western equatorial South Atlantic Ocean. The vertical movements of 35 elasmobranch individuals were tracked during an overall total of 1911 days. Clear relationships between species' feeding habits, maximum diving depths, and proportion of time spent either in epipelagic or in surface waters were evidenced by Bayesian generalized linear mixed models and multivariate analysis. Filter-feeders made most use of deep waters from the mesopelagic and bathypelagic and shifted their diving depths in phase with diel vertical migrations of the deep scattering layer, i.e., shallower during the night and deeper during the day. Specialists exhibited distinct diving patterns in epipelagic and mesopelagic waters across the diel period which are potentially indicative of habitat partitioning, whereas generalists were more surface-oriented but also explored deeper waters compared to specialists. The trophic level also seemed to influence elasmobranch maximum diving depths, which tended to become shallower as species' trophic level increased. These results corroborate previous evidence of widespread vertical habitat partitioning among sympatric pelagic predators and depict a trophic-mediated structuring of the pelagic environment where top-down control may be exerted at different depths by distinct species. Further research is yet required to understand the role of elasmobranch vertical movements in structuring pelagic habitats as well as to guide ecosystem-based fisheries management aimed at reducing species susceptibility to fishing gear and at preserving the structure and functionality of marine trophic networks.
Preprint
Chondrichthyan fishes are among the most threatened vertebrates on the planet because many species have slow life histories that are outpaced by intense fishing. The Western Central Atlantic Ocean, which includes the greater Caribbean, is a hotspot of chondrichthyan biodiversity and abundance, but is historically characterized by extensive shark and ray fisheries and a lack of sufficient data for effective management and conservation. To inform future research and management decisions, we analyzed patterns in chondrichthyan extinction risk, reconstructed catches, and regulations in this region. We summarized the extinction risk of 180 sharks, rays, and chimaeras using contemporary IUCN Red List assessments and found that over one-third (35.6%) were assessed as Vulnerable, Endangered, or Critically Endangered largely due to fishing. Reconstructed catches from 1950 to 2016 reached their peak in 1992, then declined by 40.2% through the end of the series. The United States, Venezuela, and Mexico were responsible for most catches and hosted large proportions of the regional distributions of threatened species; these countries therefore held the greatest responsibility for chondrichthyan management. The abundance and resolution of fisheries landings data were poor in much of the region, and national-level regulations varied widely across jurisdictions. Deepwater fisheries represent an emerging threat, although many deepwater chondrichthyans currently find refuge beyond the depths of most fisheries. Regional collaboration as well as effective and enforceable management informed by more complete fisheries data, particularly from small-scale fisheries, are required to protect and recover threatened species and ensure sustainable fisheries.
Conference Paper
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The domain of fish resources and fishing technology has several aspects that can be used as indicators of overfishing in a certain water area. It is very important to know in fisheries management so that the process can run optimally and sustainably. This study uses EAFM as a tool to assess the sustainability of fish resources and fishing technology in Palabuhanratu Archipelago Fishing Port. The data were obtained from interviews and questionnaires given to fishermen representing the capacity and size of their vessels. The results show that in the fish resource domain, there are two indicators that have low sustainability values, namely the Catch per Unit Effort (CpUE) and the proportion of juvenile fish. While in the domain of fishing technology, indicators that have less sustainability value are modification of fishing gear and fishery capacity. The low values of these four indicators indicate that there is a tendency for overfishing around these waters so control efforts are needed to be more sustainable.
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In recent years, much attention has been focused on the impact of climate change, particularly via ocean acidification (OA), on marine organisms. Studying the impact of OA on long-living organisms, such as sharks, is especially challenging. When the ocean waters absorb anthropogenic carbon dioxide (CO2), slow-growing shark species with long generation times may be subjected to stress, leading to a decrease in functionality. Our goal was to examine the behavioral and physiological responses of sharks to OA and the possible impacts on their fitness and resilience. We conducted a systematic review in line with PRISMA-Analyses, of previously reported scientific experiments. We found that most studies used CO2 partial pressures (pCO2) that reflect representative concentration pathways for the year 2100 (e.g., pH ~7.8, pCO2 ~1000 μatm). Since there is a considerable knowledge gap on the effect of OA on sharks, we utilized existing data on bony fish to synthesize the available knowledge. Given the similarities between the behaviors and physiology of these two superclasses’ to changes in CO2 and pH levels, there is merit in including the available information on bony fish as well. Several studies indicated a decrease in shark fitness in relation to increased OA and CO2 levels. However, the decrease was species-specific and influenced by the intensity of the change in atmospheric CO2 concentration and other anthropogenic and environmental factors (e.g., fishing, temperature). Most studies involved only limited exposure to future environmental conditions and were conducted on benthic shark species studied in the laboratory rather than on apex predator species. While knowledge gaps exist, and more research is required, we conclude that anthropogenic factors are likely contributing to shark species’ vulnerability worldwide. However, the impact of OA on the long-term stability of shark populations is not unequivocal.
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The population genetic structure and female philopatry to nursery grounds of the scalloped hammerhead shark (Sphyrna lewini) were studied in different mangrove estuaries along the Mexican Pacific coast containing putative nurseries. These nurseries were grouped into northern (Sinaloa-Nayarit), central (Jalisco), and southern (Oaxaca-Chiapas) regions. Neonates and young of the year were collected near estuaries or river inlets, and their genetic variation was compared based on mitochondrial DNA (mtDNA) genome sequences and 11 nuclear microsatellite loci. The mtDNA analysis showed significant differences between the abovementioned regions, accompanied by genetic homogeneity of microsatellites. Based on the genetic divergence of mtDNA and the lack of differences in nuclear markers, our results are congruent with female philopatry to nursery areas, as observed in other shark species. The parentage analysis applied to the microsatellite data showed moderate levels of relatedness among individuals within nurseries, suggesting philopatry as a cause of the observed results. The pattern of nursery grounds of the scalloped hammerhead shark in the Mexican Pacific seems to be regional, as no differences were observed between neighboring estuaries within each studied region. These findings are relevant for delineating conservation plans to preserve key populations and minimize the effects of commercial fisheries.
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Although exceedingly rare, shark attacks have a disproportionately large impact on human behavior, often resulting in shark culls. Due to the invasive nature of shark culls, innovating and testing non-invasive deterrent technologies that may minimize the potential for a rare negative shark encounter has become a conservation priority. One such mitigation approach is barriers, such as exclusion nets and the Sharksafe barrier. With both technologies exhibiting limitations and/or ineffectiveness (e.g., Sharksafe barrier), the development of a more effective technology was warranted. Therefore, this study had two key objectives: (1) to determine if DC 12 Volts 180 Newtons electromagnets can produce deterrent responses in the bull shark (Carcharhinus leucas) and (2) to determine if a newly designed and eco-friendly Exclusion barrier exhibits enhanced C. leucas deterrent capabilities when directly compared to the Sharksafe barrier. Based on 100 baited apparatus trials, electromagnetically treated baits resulted in significantly greater avoidance and reduced feeding frequencies. Furthermore, Poisson generalized linear mixed effect model analyses based on 27, 1-h trials illustrated that the Exclusion barrier region resulted in the greatest avoidance and lowest entrance and exit frequencies when compared to the control and Sharksafe barrier regions. Although the Exclusion barrier did not exclude all interacting sharks, the technology provided superior deterrent efficacy in relation to the Sharksafe barrier. Therefore, with many shark populations exhibiting precipitous declines, continued research on this novel technology on potentially dangerous shark species (e.g., white sharks—Carcharodon carcharias) and in varying ecological conditions (e.g., a high energy coastline) is warranted.
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The feeding habits of Urotrygon microphthalmum, a Critically Endangered (CR) species, were investigated through stomach contents analysis from specimens caught on bottom double rigged otter trawls in Pernambuco state, Brazil, between March of 2010 and March of 2012. A total of 338 stomachs were analyzed, and 31 food items were identified in the diet of U. microphthalmum. The species ingests mainly shrimps. The diets between males and females were not different, and an ontogenetic diet shift was not observed. The estimated species’ trophic level is 3.5, classifying it as a secondary order consumer.
Chapter
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ntroduction Chondrichthyan fishes are probably the most successful of all fishes if success is measured in terms of historical endurance, based on ability to survive the mass extinctions of the last 400 million years or so. They are essentially defined by a cartilaginous skeleton that is superficially mineralized by prismatic calcifications (tesserae) and by the modification, within males, of mixopterygia (claspers) for the purpose of internal fertilization. It is generally accepted that the Class Chondrichthyes is a monophyletic group divisible into two sister taxa, the Elasmobranchii and Holocephali, and that extant chondrichthyans (sharks, skates, rays, and chimaeras) are derivable from Mesozoic forms. Yet, how these forms relate to the distinctly more diverse Paleozoic forms and even the relationship of the Chondrichthyes to all other fishes are poorly resolved issues. Unquestionable evidence of cartilaginous fishes extends to the Lower Devonian or even to the Silurian if isolated scales (putatively shark in origin) can be considered with any confidence. However, in reviewing such information it is imperative to consider what features or characters ensure that these earliest preserved vestiges are remains of a chondrichthyan form rather than a non-chondrichthyan. The purpose of this chapter is to discuss the evidence for the origin, diversification, and life histories of the Chondrichthyes, to address trends in their morphological divergence and innovation, and to explore the possible relationships between fossil and modern forms. In a general discussion of relationships, we adopt the classification scheme for shark and sharklike fishes put forth by Compagno (2001), as a consensus of the analyses of Compagno (1984), Shirai (1996), and de Carvalho (1996). The classification scheme used to describe the relationships of all Chondrichthyes is that developed in Lund and Grogan (1997a, b, in press, a, b) and Grogan and Lund (2000).
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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, while each of the investigated species showed a constant trend in mean annual weight. There were high proportions of juveniles in the catches of dusky shark (100%), dusky kob (92%) and giant guitarfish (78%). Improvements made to the structure of shore angling competitions and the overall contribution of competition angling to resource management in South Africa is discussed.
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The bycatch of Australia's northern prawn fishery (NPF) comprises 56 elasmobranch species (16 families). The impact of this fishery on the sustainability of these species has not been addressed. We obtained estimates of catch rates and the within-net survival of elasmobranchs. Carcharhinus tilstoni, C. dussumieri, Rhynchobatus djiddensis, and Himantura toshi represented 65% of the bycatch. For most species, >50% of individuals in the bycatch were immature, and some species recruited to the fishery at birth. For all species combined, 66% of individuals in the bycatch died in the trawl net. The relative sustainability of elasmobranchs caught as bycatch was examined by ranking species with respect to their susceptibility to capture and mortality due to prawn trawling and with respect to their capacity to recover once the population was depleted. The species that were least likely to be sustainable were four species of pristids, Dasyatis brevicaudata, and Himantura jenkinsii. These are bottom-associated batoids that feed on benthic organisms and are highly susceptible to capture in prawn trawls. The recovery capacity of these species was also low according to our criteria. Our results provide a valuable first step towards ensuring the sustainability of elasmobranchs that are caught as bycatch by highlighting species for management and research. The effectiveness of turtle excluder devices (TEDs) in reducing elasmobranch bycatch varied greatly among species but was generally not very effective because most of the captured species were small.
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Published life-history parameters for sharks, skates, and rays over a wide geographic range were used to develop predictive models to estimate parameters that are difficult to measure or have not been previously estimated in elasmobranch species. We determined empirical relationships between body size (total length) and length at maturity (Lm) and age at maturity (Tm). The data used in determining these empirical relationships, the von Bertalanffy parameters asymptotic length (L∞) and growth rate (k), and natural mortality (M) and maximum age (Tmax) were used to describe the life-history strategies of elasmobranch fishes. M/k and Beverton's growth-maturity-longevity plots were used to make comparisons between teleost fishes, reptiles, and elasmobranchs. We found that the M/k ratio in elasmobranchs is significantly different from those for other fish and reptile taxa. We linked elasmobranch species fecundity (f) and Tm to potential vulnerability to population decline under exploitation. We found that larger species of elasmobranchs have lower growth rates (k) and potential population increases (r ′). Elasmobranchs can be categorized by species maximum length to determine susceptibility of decline under exploitation. Generally, species greater than 100 cm are characterized by life-history and population traits that place them at greater risk of population decline.
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Ecosystem-orientated thinking is increasingly incorporated into fishery management. Given the complexity of ecosystem processes, there is a need to evaluate the tools used to steer this thinking critically. ECOPATH with ECOSIM (EwE), an aggregate system-modelling package, is currently the most widely employed approach to assess the ecosystem effects of fishing. The basic equations and assumptions, strengths and weaknesses, and the potential of this approach to contribute to practical fisheries management advice are reviewed. Strengths include the structured parameterization framework, the inclusion of a well-balanced level of conceptual realism, a novel representation of predator-prey interaction terms, and the inclusion of a Bayes-like approach (ECORANGER) to take account of the uncertainty associated with values for model inputs. Weaknesses in model structure include the constraining nature of the mass-balance assumption (of ECOPATH) for initiating projections, the questionable handling of life history responses such as compensatory changes in the natural mortality rates of marine mammals, overcompensatory stock-recruit relationships that result from default parameter settings, possible problems in extrapolating from the microscale to the macroscale, as well as some (not too far-reaching) mathematical inconsistencies in the underlying equations. There is a paucity of systematic and stepwise investigations into model behaviour and properties, and users are cautioned against non-critical use of the default settings. An important limitation related to the predominant use of EwE as a "black-box" modelling tool is that some users fail to consider a range of alternative interaction representations. As with all multispecies approaches, the major limitation in applying the EwE approach lies in the quality and quantity of available data. Current EwE applications generally do not adequately address uncertainty in data inputs and model structure. Prudent EwE applications that utilize good data and are based upon rigorous statistical analyses can complement the quantitative predictions of traditional single-species models. They could be particularly useful in some contexts if output in the form of probability distributions encompassing a range of likely ecosystem responses were to be coupled with attempts to extend Operational Management Procedure (OMP) approaches to fisheries management beyond the singlespecies level. In particular, such applications could serve as the operating models of the underlying dynamics that are used for computer simulation testing of OMPs.
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The geographic and the bathymetric distribution of offshore demersal cartilaginous fish off the west coast of southern Africa are reviewed. The results were collected during 12 cruises of F.R.S. Africana between 1986 and 1990. The area covered was between Walvis Bay (23°S, 14°E) and the Agulhas Bank west of Cape Agulhas (36°S, 20°E) over a depth range of 33–1 016 m. In all, 55 species of cartilaginous fish were collected, including 32 sharks, 17 rays and six chimaeras, on 869 stations and representing 3 092 station records. Computer-generated maps and station lists are presented for the species in the sample, and the distribution records, including records from the literature, are reviewed and discussed for these species and 12 more demersal species not collected during the survey. The survey revealed many range extensions for described species. West Coast demersal cartilaginous fish show zonation by depth and latitude, and groups of species with similar depth and latitudinal distributions were apparent. These groups are defined and discussed, along with summer-winter distributional differences, aggregations of records, sympatry and allopatry in related species, and relative diversity over 50-m depth increments and one-degree latitudinal bands.
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Published life-history parameters for sharks, skates, and rays over a wide geographic range were used to develop predictive models to estimate parameters that are difficult to measure or have not been previously estimated in elasmobranch species. We determined empirical relationships between body size (total length) and length at maturity (L m ) and age at maturity (T m ). The data used in determining these empirical relationships, the von Bertalanffy parameters asymptotic length (L [Formula: see text] ) and growth rate (k), and natural mortality (M) and maximum age (T max ) were used to describe the life-history strategies of elasmobranch fishes. M/k and Beverton's growth–maturity–longevity plots were used to make comparisons between teleost fishes, reptiles, and elasmobranchs. We found that the M/k ratio in elasmobranchs is significantly different from those for other fish and reptile taxa. We linked elasmobranch species fecundity (f) and T m to potential vulnerability to population decline under exploitation. We found that larger species of elasmobranchs have lower growth rates (k) and potential population increases (r'). Elasmobranchs can be categorized by species maximum length to determine susceptibility of decline under exploitation. Generally, species greater than 100 cm are characterized by life-history and population traits that place them at greater risk of population decline.
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1. Fishing spans all oceans and the impact on ocean predators such as sharks and rays is largely unknown. A lack of data and complicated jurisdictional issues present particular challenges for assessing and conserving high seas biodiversity. It is clear, however, that pelagic sharks and rays of the open ocean are subject to high and often unrestricted levels of mortality from bycatch and targeted fisheries for their meat and valuable fins. 2. These species exhibit a wide range of life-history characteristics, but many have relatively low productivity and consequently relatively high intrinsic vulnerability to over-exploitation. The IUCN}World Conservation Union Red List criteria were used to assess the global status of 21 oceanic pelagic shark and ray species. 3. Three-quarters (16) of these species are classified as Threatened or Near Threatened. Eleven species are globally threatened with higher risk of extinction: the giant devilray is Endangered, ten sharks are Vulnerable and a further five species are Near Threatened. Threat status depends on the interaction between the demographic resilience of the species and intensity of fisheries exploitation. 4. Most threatened species, like the shortfin mako shark, have low population increase rates and suffer high fishing mortality throughout their range. Species with a lower risk of extinction have either fast, resilient life histories (e.g. pelagic stingray) or are species with slow, less resilient life histories but subject to fisheries management (e.g. salmon shark). 5. Recommendations, including implementing and enforcing finning bans and catch limits, are made to guide effective conservation and management of these sharks and rays.
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Shark and ray populations appear to be extremely vulnerable to flshing pressure. In this paper, we inves- tigated the dynamics of elasmobranch populations of the upper Tyrrhenian Sea over more than a century by analyzing data from commercial landings of flsh traps, literature records and scientiflc trawl surveys. These data were integrated using generalized linear models, in which the change in abundance as well as depth distribution was modelled for each species. Of 36 species recognized to inhabit the coastal water of the investigated area in the 20th century 17 have declined in abundance to undetectable levels in all depths. Others are still flshed at deeper grounds, but even there they show signs of depletion due to flshing pressure. This paper analyzes a small sector of the Mediterranean Sea, but its results appear to agree with other investigations in the basin. We believe the magnitude of depletion of the elasmobranch community in the whole Mediterranean region be largely underestimated and require an immediate large scale reassessment to prevent multiple cases of local extinctions.
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We identify changes in the pelagic fish community of the tropical Pacific Ocean by comparing recent data collected by observers on longline fishing vessels with data from a 1950s scientific survey when industrial fishing commenced. A major shift in size composition and indices of species abundance and community biomass accompanied the start of fishing. The largest and most abundant predators, such as sharks and large tunas, suffered the greatest declines in abundance (21% on average). They also showed striking reductions in mean body mass. For example, the mean mass of blue shark (Prionace glauca) was 52 kg in the 1950s compared to 22 kg in the 1990s. The estimated abundance of this species was 13% of that in the 1950s. Overall, the biomass of large predators fell by a factor of 10 between the periods. By contrast, several small and formerly rare species increased in abundance, e.g., pelagic stingray ( Dasyatis violacea). However, the increases in small species did not balance the reductions in the biomass of large predators. Of three possible explanations (fishing, environmental variation, and sampling bias), available ev- idence indicates fishing to be the most likely cause for the observed patterns.