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Abstract

Sharks are considered the apex predator of coral reefs, but the consequencesof their global depletion are uncertain. Here we explore the ecological roles of sharks on coral reefs and, conversely, the importance of reefs for sharks. We find that most reef-associated shark species do not act as apex predators but instead function as mesopredators along with a diverse group of reef fish. While sharks perform important direct and indirect ecological roles, the evidence to support hypothesised shark-driven trophic cascades that benefit corals is weak and equivocal. Coral reefs provide some functional benefits to sharks, but sharks do not appear to favour healthier reef environments.Restoring popula- tions of sharks is important and can yet deliver ecological surprise.

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... Worldwide, shark stocks are severely under pressure due to overexploited and unregulated fisheries [1,2]. Although sharks are targeted in fisheries operating in the Arabian/Persian Gulf (hereafter the Gulf), information on regulatory and law enactment remains deficient [3][4][5]. ...
... Due to their size and predatory behavioral traits, reef sharks play a very important ecological function. Additionally, a recent study revealed that most reef-associated shark species do not act as apex predators, but instead function as mesopredators (a species that occupy a high trophic position but are below apex predators and are themselves vulnerable to predation) along with various reef fishes [1]. Another study also supports this stance with evidence and data collected from stomach contents and stable isotopes analysis to assess diet and trophic position for three common species of reef sharks. ...
... Most fishery scientists believe that sharks have the potential to modify the community structure of marine food webs, either through direct or indirect interactions resulting from the consumption of prey and/or the alteration of species' behavior as a result of their presence [21]. Hypothesized shark-driven trophic cascades that benefit corals however remain weak, equivocal, and in many cases unsupported [1]. Even so, restoring shark populations remain critical as part of the ecosystem processes as reef-associated mesopredatory sharks: i) provide nutrient cycling between adjacent pelagic-and reef habitats [22,23]; ii) play an important role as facultative scavengers (consuming carcasses); and iii) they have the potential to exert top-down control of invasive species [24]. ...
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Challenges that relate to shark conservation may well be a combination of the intersection of people's livelihoods and the ineffectiveness of management strategies. Given the current protection initiatives as well as the implementation of tighter laws restricting hunting and trade, shark conservation is still recognized as a major environmental challenge. The United Arab Emirates (U.A.E.) is used as an export hub and is one of the primary exporters of shark fins to Hong Kong, with a large proportion of fins traded to be from species at high risk of global extinction. The present-day management of shark fisheries also shows shortcomings concerning lawfulness, specifically those relating to regulatory compliance, fishing techniques, and control of finning occurrences. These concerns are not unique to the U.A.E. but emphasize the fact that there are far-reaching problems related to shark conservation. Even in a milieu of strengthened conservation measures and revised legislature, existing information on the effectiveness of a shark finning ban may still be misleading when viewed in the light of over-exploitation and global species abundance. It is therefore important that proper management must be implemented at the inception of shark fisheries. For the U.A.E., this has not always been the case. Instead, the trend was one of limited control and lack of compliance, unfortunately, resulting in a rapid decline in shark abundance, to the point where sharks struggle to recover. This paper focuses on the importance of the species, reviews the current monitoring framework, and seeks to enhance shark protection.
... Reef sharks are among the largest resident predators on coral reefs, playing a variety of ecological roles that could potentially be important for reef communities [1][2][3] . Due to their conservative demography, reef sharks are particularly vulnerable to anthropogenic mortalities from fisheries, particularly overfishing and bycatch [4][5][6] . ...
... The inability of MPAs to encompass individuals' movements has been identified as contributing to their failure to protect mobile species 18,23,24 . Through a meta-analysis of 87 MPAs around the world, size and isolation by deep water or sand have been highlighted as key factors in MPAs' efficiency to protect predator species 25 , with only a small subset of these MPAs qualified as large (> 100 km 2 ). For coastal sharks, MPAs > 20,000 km 2 have been identified as the most efficient 6 . ...
... The grey reef shark, Carcharhinus amblyrhynchos, is one of the most common reef shark species in the Indo-Pacific 2,8,9,11,[32][33][34] . The estimated home range for this species 35,36 , along with its high level of site residency [37][38][39] and long-term fidelity [40][41][42] , suggest that MPAs > 100 km 2 would be appropriate for its protection. ...
Article
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Dramatic declines in reef shark populations have been documented worldwide in response to human activities. Marine Protected Areas (MPAs) offer a useful mechanism to protect these species and their roles in coral reef ecosystems. The effectiveness of MPAs notably relies on compliance together with sufficient size to encompass animal home range. Here, we measured home range of 147 grey reef sharks, Carcharhinus amblyrhynchos, using acoustic telemetry in New Caledonia. The distribution of home range was then compared to local MPA sizes. We report a home range of 12 km2 of reef for the species with strong differences between adult males (21 km2), adult females (4.4 km2) and juveniles (6.2 km2 for males, 2.7 km2 for females). Whereas local historic MPA size seemed adequate to protect reef shark home range in general, these were clearly too small when considering adult males only, which is consistent with the reported failure of MPAs to protect sharks in New Caledonia. Fortunately, the recent implementation of several orders of magnitude larger MPAs in New Caledonia and abroad show that recent Indo-Pacific MPAs are now sufficiently large to protect the home ranges of this species, including males, across its geographical range. However, protection efforts are concentrated in a few regions and cannot provide adequate protection at a global scale.
... Such constrained definitions of the top predator role have been challenged in the context of coral reef fish food webs. Reef sharks, for example, have been documented foraging on taxa across a range of trophic levels, including nearshore pelagic fishes [17] and lower trophic level fish and invertebrates in the reef habitat [18]. Similarly, the diet of the predatory two-spot snapper (Lutjanus bohar) across the Line Islands has been shown to converge on an estimated trophic level similar to that of smaller bodied teleost predators [19]. ...
... Similarly, the diet of the predatory two-spot snapper (Lutjanus bohar) across the Line Islands has been shown to converge on an estimated trophic level similar to that of smaller bodied teleost predators [19]. Given such evidence, it has been proposed that reef sharks and other large-bodied predatory fishes on coral reefs be designated as 'mesopredators' [18,20]. However, there is a distinct role played by the large-bodied predators on a coral reef, most importantly being their capacity to predate upon a particularly wide range of potential prey. ...
... Evidence of trophic cascades on coral reefs is limited, likely due to the high diversity of species and relative functional redundancy among coral reef taxa [41,45]. Models suggesting that changes in density of sharks on coral reefs can create a trophic cascade (i.e. through the release of mesopredatory prey and the concomitant decrease in lower trophic level prey) have been challenged based upon similar considerations of high trophic complexity of most reef food webs [18,46]. However, recent evidence suggests that the diets of mesopredators (i.e. ...
Article
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Predation is ubiquitous on coral reefs. Among the most charismatic group of reef predators are the top predatory fishes, including sharks and large-bodied bony fishes. Despite the threat presented by top predators, data describing their realized effects on reef community structure and functioning are challenging to produce. Many innovative studies have capitalized on natural experimental conditions to explore predator effects on reefs. Gradients in predator density have been created by spatial patterning of fisheries management. Evidence of prey release has been observed across some reefs, namely that potential prey increase in density when predator density is reduced. While such studies search for evidence of prey release among broad groups or guilds of potential prey, a subset of studies have sought evidence of release at finer population levels. We find that some groups of fishes are particularly vulnerable to the effects of predators and more able to capitalize demographically when predator density is reduced. For example, territorial damselfish appear to realize reliable population expansion with the reduction in predator density, likely because their aggressive, defensive behavior makes them distinctly vulnerable to predation. Relatedly, individual fishes that suffer from debilitating conditions, such as heavy parasite loads, appear to realize relatively stronger levels of prey release with reduced predator density. Studying the effects of predators on coral reefs remains a timely pursuit, and we argue that efforts to focus on the specifics of vulnerability to predation among potential prey and other context-specific dimensions of mortality hold promise to expand our knowledge.
... maximum body size, body mass, trophic group, schooling behaviour, metabolic rate and mobility; Bellwood et al., 2019;Tavares et al., 2019). The role of top predators is linked to high trophic levels, large body sizes and body mass (Roff et al., 2016;Tavares et al., 2019), while effective grazing appears related to eye diameter and position, gape position and shape, total gut length and body size (Bonaldo et al., 2014;Villéger et al., 2017). A single trait as body size, for example, is related to bioturbation (Bonaldo et al., 2014;Tavares et al., 2019), individual mobility (Villéger et al., 2017), nutrient cycling (Allgeier et al., 2014;Tavares et al., 2019), trophic regulation and community structuring in marine vertebrates (Tavares et al., 2019). ...
... Further, sharks share life-history traits, as slow growth and late maturity, which increase their vulnerability and hamper stock recovery (Dulvy et al., 2014;Stevens et al., 2000). Despite the important role of sharks on ecosystems, the redundancy among top predators is questionable since most shark species are now considered mesopredators given reductions of their size and body mass (Roff et al., 2016). This result reinforces threats to marine mesopredators since the scarcity of top predators makes this functional group the next to be depleted from marine food webs (Ferretti et al., 2010;Myers et al., 2007;Roff et al., 2016). ...
... Despite the important role of sharks on ecosystems, the redundancy among top predators is questionable since most shark species are now considered mesopredators given reductions of their size and body mass (Roff et al., 2016). This result reinforces threats to marine mesopredators since the scarcity of top predators makes this functional group the next to be depleted from marine food webs (Ferretti et al., 2010;Myers et al., 2007;Roff et al., 2016). ...
Article
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Aim Marine vertebrates play key functional roles on reef ecosystems. Despite their phylogenetic distance, different vertebrate lineages could play similar functions on reefs, which has been overlooked by current research on marine functional biogeography. We provide the first comprehensive assessment of the functional structure and inventory of ecosystem functions delivered by 224 vertebrates—marine mammals, sea turtles, sharks, rays and bony fish—in Atlantic Ocean reefs. Location Atlantic Ocean reefs. Methods We compiled six species-level traits and investigated geographical patterns of functional richness (FRic), functional uniqueness (FUn) and specialization (FSpe) in 83 assemblages. Additionally, we simulate the effects of marine vertebrate species’ extinction on functional diversity metrics. Results Sharks, rays and bony fish species had the highest overlap in functional space (30.94%), while turtles overlapped mainly with bony fishes (1.76%). The functional structure of vertebrate assemblages is not homogeneous across the Atlantic. While functional richness peaks in the Caribbean (a “functional hotspot”), this region depicts low-to-intermediate functional uniqueness and functional specialization levels. Despite the large proportion of threatened top predator species (53.1%), mainly large-bodied sharks, it is the loss of mesopredator species that will severely impact (up to 94% of functional loss) the functional space of vertebrate assemblages in Atlantic Ocean reefs. Main conclusions Our study reveals that functional richness patterns of vertebrate assemblages differ across Atlantic Ocean reefs. Despite the low values of functional uniqueness and specialization in some reef assemblages, reef functioning can still be compromised due to species’ extinctions. The impact of mesopredators’ loss over the functional structure of vertebrate assemblages is worrisome since this group holds a considerable proportion of threatened species (20.1%) and is next in line considering the anthropogenic impacts over high trophic level species.
... Sharks as predators are a major component of marine food webs [1,2]. Among them, the larger species, such as the great and the scalloped hammerhead sharks Sphyrna mokarran and S. lewini and the tiger shark, Galeocerdo cuvier, are transient apex predators on coral reefs [2,3]. They are capable of structuring coral reef food webs both directly through predation and indirectly by modifying prey behavior [3]. ...
... Among them, the larger species, such as the great and the scalloped hammerhead sharks Sphyrna mokarran and S. lewini and the tiger shark, Galeocerdo cuvier, are transient apex predators on coral reefs [2,3]. They are capable of structuring coral reef food webs both directly through predation and indirectly by modifying prey behavior [3]. In contrast, most shark species, among which the gray reef shark, Carcharhinus amblyrhynchos, the Galapagos shark, C. galapagensis, the blacktip reef shark, C. melanopterus, are reef-associated meso-predators [2,3]. ...
... They are capable of structuring coral reef food webs both directly through predation and indirectly by modifying prey behavior [3]. In contrast, most shark species, among which the gray reef shark, Carcharhinus amblyrhynchos, the Galapagos shark, C. galapagensis, the blacktip reef shark, C. melanopterus, are reef-associated meso-predators [2,3]. They share functional redundancy among each other and with large piscivorous fishes such as groupers or snappers; all are assigned to the trophic group of high-level meso-predators and are considered to exert a limited influence on the community structure [2][3][4]. ...
Article
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Sharks have declined worldwide and remote sanctuaries are becoming crucial for shark conservation. The southwest Indian Ocean is a hotspot of both terrestrial and marine biodiversity mostly impacted by anthropogenic damage. Sharks were observed during surveys performed from April to June 2013 in the virtually pristine coral reefs around Europa Island, a remote Marine Protected Area located in the southern Mozambique Channel. Observation events comprised 67 1-hour scientific dives between 5-35m depth and 7 snorkeling inspections , as well as 4 dinghy-based observations in the shallow lagoon. In a period of 24 days, 475 sharks were tallied. Carcharhinus galapagensis was most encountered and contributed 20% of the abundance during diving, followed by C. albimarginatus (10%). Both species were more abundant between 11-14h, and on the exposed sides of the island. Numbers of Sphyrna lewini were highest with 370 individuals windward and leeward, mostly schooling. S. lewini aggregations in the area are hypothesized to be attracted to the seamount archipelago offering favorable conditions for deep incursions and of which Europa Island forms part. C. amblyrhynchos, Galeocerdo cuvier and S. mokarran were uncommon, while there was an additional observation of Rhincodon typus. The lagoon of Europa was a nursery ground for C. melanopterus where it was the only species present. A total of 8 species was recorded, contributing to the shark diversity of 15 species reported from Europa since 1952 in the scientific and gray literature. Overall, with the occurrence of several species of apex predators in addition to that of R. typus, large schools of S. lewini, fair numbers of reef sharks and a nursery of C. melanopterus, Europa's sharks constitute a significant reservoir of biodiversity, which contributes to preserve the functioning of the ecosystem. Our observations highlight the relevance of Europa Island for shark conservation and the need for shark-targeted management in the EEZ of both Europa and Bassas da India.
... Sharks as predators are a major component of marine food webs [1,2]. Among them, the larger species, such as the great and the scalloped hammerhead sharks Sphyrna mokarran and S. lewini and the tiger shark, Galeocerdo cuvier, are transient apex predators on coral reefs [2,3]. They are capable of structuring coral reef food webs both directly through predation and indirectly by modifying prey behavior [3]. ...
... Among them, the larger species, such as the great and the scalloped hammerhead sharks Sphyrna mokarran and S. lewini and the tiger shark, Galeocerdo cuvier, are transient apex predators on coral reefs [2,3]. They are capable of structuring coral reef food webs both directly through predation and indirectly by modifying prey behavior [3]. In contrast, most shark species, among which the gray reef shark, Carcharhinus amblyrhynchos, the Galapagos shark, C. galapagensis, the blacktip reef shark, C. melanopterus, are reef-associated meso-predators [2,3]. ...
... They are capable of structuring coral reef food webs both directly through predation and indirectly by modifying prey behavior [3]. In contrast, most shark species, among which the gray reef shark, Carcharhinus amblyrhynchos, the Galapagos shark, C. galapagensis, the blacktip reef shark, C. melanopterus, are reef-associated meso-predators [2,3]. They share functional redundancy among each other and with large piscivorous fishes such as groupers or snappers; all are assigned to the trophic group of high-level meso-predators and are considered to exert a limited influence on the community structure [2][3][4]. ...
Article
Full-text available
Sharks have declined worldwide and remote sanctuaries are becoming crucial for shark conservation. The southwest Indian Ocean is a hotspot of both terrestrial and marine biodiversity mostly impacted by anthropogenic damage. Sharks were observed during surveys performed from April to June 2013 in the virtually pristine coral reefs around Europa Island, a remote Marine Protected Area located in the southern Mozambique Channel. Observation events comprised 67 1-hour scientific dives between 5 – 35m depth and 7 snorkeling inspections, as well as 4 dinghy-based observations in the shallow lagoon. In a period of 24 days, 475 sharks were tallied. Carcharhinus galapagensis was most encountered and contributed 20% of the abundance during diving, followed by C . albimarginatus (10%). Both species were more abundant between 11-14h, and on the exposed sides of the island. Numbers of Sphyrna lewini were highest with 370 individuals windward and leeward, mostly schooling. S . lewini aggregations in the area are hypothesized to be attracted to the seamount archipelago offering favorable conditions for deep incursions and of which Europa Island forms part. C . amblyrhynchos , Galeocerdo cuvier and S . mokarran were uncommon, while there was an additional observation of Rhincodon typus . The lagoon of Europa was a nursery ground for C . melanopterus where it was the only species present. A total of 8 species was recorded, contributing to the shark diversity of 15 species reported from Europa since 1952 in the scientific and gray literature. Overall, with the occurrence of several species of apex predators in addition to that of R . typus , large schools of S . lewini , fair numbers of reef sharks and a nursery of C . melanopterus , Europa’s sharks constitute a significant reservoir of biodiversity, which contributes to preserve the functioning of the ecosystem. Our observations highlight the relevance of Europa Island for shark conservation and the need for shark-targeted management in the EEZ of both Europa and Bassas da India.
... Sharks on many Caribbean coral reefs could have experienced earlier and more intense exposure to human stressors than their offshore counterparts, owing to their greater proximity to human populations (3,7), the antiquity of fishing (8)(9)(10), and the widespread degradation of reef ecosystems, which preceded systematic monitoring (1,(11)(12)(13). Without baseline data to document what has been lost, it is challenging to implement effective management practices and to understand sharks' natural functions as mobile predators on reefs (14,15). ...
... Reef sharks have been depleted in many regions (6,39) including the Caribbean (3), yet we do not know what shark carrying capacities were on Caribbean reefs before people began fishing and altering the landscape, thus hindering efforts to set management targets informed by local expected conditions. It is also unclear whether shark communities were compositionally different in the past and how any structural changes might have affected their ecological functions on reefs (15). Our approach, which leverages shark dermal denticles preserved in mid-Holocene and modern reef sediments, helps resolve this issue. ...
... The denticle record can contribute historical perspective to how shark declines might have affected ecosystem processes and can help test predictions rooted in ecological theory. Theory predicts that the threefold loss of meso and apex predators likely altered food web structure and stability through a decrease in predation and scavenging and a possible loss of functional redundancy (15,(67)(68)(69). The removal of predators might have also diminished nonconsumptive effects on prey behavior and foraging (70), nutrient cycling (15,66), and cross-ecosystem linkages (71). ...
Article
Significance How abundant were sharks on Caribbean coral reefs before human impact? To explore this question, we recovered fossilized shark dermal denticles (scales) from a ∼7,000-y-old reef in western Caribbean Panama and compared them with denticles found on modern reefs in the same area. Our data suggest that sharks were over three times more numerous before humans began using marine resources in the area and that shark communities were compositionally different in the past, containing a higher proportion of fast-swimming, pelagic sharks. This reconstruction of preexploitation shark communities using fossil denticle assemblages demonstrates their potential to help contextualize recent declines in shark abundance, examine the ecological consequences of those declines, and guide shark management.
... Obviously, such controls can coexist and vary in intensity trough time and uncertainty on which mechanism is dominant remains in a vast majority of ecosystems (Cury et al., 2000;Hunter and Price, 1992;Ritchie and Johnson, 2009;Roff et al., 2016). An example of such complexity is the top-down control exercised by sea otters (Enhydra lutris nereis) on purple sea urchins (Strongylocentrotus purpuratus) and kelp forests in the Aleutian archipelago (Estes and Palmisano, 1974;Reisewitz et al., 2006). ...
... Putative top-down cascading effects have been observed in coastal environment but can be difficult to detect as they are often masked or inversed by fishery or environmental pressures affecting mesopredators release. Moreover, undescribed predator-prey interactions or lack of knowledge on ecosystems functioning make the analysis of trophic cascades difficult in marine environments (e.g., Ferretti et al., 2010;Roff et al., 2016). Understanding the trophic ecology of top predator species is therefore fundamental, particularly in regions where sharks are critically overfished to gain information on the possible effects of their decline. ...
... Coastal ecosystems are key habitats for many shark species, encompassing a broad diversity of dynamics, shaping their distributions and movements worldwide. Due to their high productivity, coastal environments first represent an important source of food like in mangroves or coral reefs (Roff et al., 2016). These ecosystems also cover a broad range of functionalities, such as reproduction, resting (e.g., to avoid intra-guild aggressive behaviors) or thermoregulation areas to maintain/restore energy needed to support metabolic rate, growth and/or embryonic development (Knip et al., 2010). ...
Thesis
Characterizing the trophic ecology of sharks is fundamental to understand the potential cascading effects of their current décline in marine ecosystems. This thesis investigates the trophic niches of shark species in Coastal and offshore ecosystems around Baja California Sur (Mexico) in both the Pacific Ocean and the Gulf of California, a region characterized by a strong pressure from artisanal fisheries. Ecologically, the guiding thread was to elucidate the importance of resource partitioning in shaping shark realized trophic niches, at both the intra- and inter-specific level. To achieve this objective, multiple trophic biomarkers were used, such as carbon, nitrogen and mercury stable isotopes, and fatty acid compositions, to describe the vertical and horizontal dimensions of shark foraging habits.At the intra-specific level, resource partitioning was supported by the use of distinct ecosystems for juvenile hammerhead sharks due to ontogenetic shifts in habitat and prey. Inter-specific resource partitioning seems to be driven by foraging at different depth within pelagic assemblages, but could also depend on local environmental conditions, such as upwelling activity. This work also characterized the life cycle of a poorly studied hammerhead species, the smooth hammerhead shark (Sphyrna zygaena). The prolonged Coastal residency of this species through ontogeny suggests significant vulnerability to local artisanal fisheries. Finallly, the demonstrated complementarity of trophic markers provides a promising insight to unravel food web structure and ecological mechanisms.
... Ecological groups were classified according to fish feeding habits: herbivores, small and large predators. Following Roff et al. (2016), we considered predators with mean sizes below 100 cm to be small predators. We classify fish with sizes > 100 cm as large predators because they occupy the highest trophic levels in heavily fished reefs where the original top trophic level species are absent or scarce (Roff et al. 2016). ...
... Following Roff et al. (2016), we considered predators with mean sizes below 100 cm to be small predators. We classify fish with sizes > 100 cm as large predators because they occupy the highest trophic levels in heavily fished reefs where the original top trophic level species are absent or scarce (Roff et al. 2016). Statistical analyses were conducted separately for each of the fish groups (e.g., target species, ornamental species, large predators/small predators, and herbivores). ...
Article
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Reef fish assemblages under fishing pressure generally exhibit a lower fish biomass, abundance, and size structure, which can be counteracted with the creation of marine protected areas (MPAs). The effectiveness of MPAs relies on enforcement and compliance, which is particularly challenging in developing countries with financial and socioeconomic limitations. By combining underwater visual surveys (UVS) and baited remote underwater video stations (BRUVS), we determined the abundance, size distribution, and biomass of economic (e.g., target and ornamental species) and ecological (e.g., small/large predators and herbivorous) indicator fish groups inside and outside a no-take MPA from the north Pacific coast of Costa Rica. The biomass of economic fish groups was not affected by protection, yet overall abundance and size distribution of fishes differed between no-take and open-fishing zones. These results suggest that although illegal fishing may be occurring inside the MPA, there are at least partial benefits of protection on particular groups within the fish assemblage. Herbivores and ornamental fishes, two groups that are targeted by the artisanal compressor fishery and by the aquarium trade, respectively, had higher biomass and were more abundant inside the no-take MPA. Additionally, large shark species (e.g., Galeocerdo cuvier, Carcharhinus leucas, C. limbatus) were only present inside the MPA. Habitat quality was particularly important for ornamental fishes which showed higher biomass in areas with high coral cover. Our study adds to a growing body of evidence suggesting that, even with limited enforcement, MPAs still provide ecological benefits for reef fish assemblages.
... Second to (but in addition to) overfishing, habitat loss and degradation resulting from coastal development, agriculture/aquaculture (such as mangrove destruction for shrimp farming), and indirectly through climate (Roff et al. 2016a) has been flagged as a threat for sharks and rays, jeopardizing over onethird (31.2%) of threatened species (Dulvy et al. 2014. This threat is particularly acute in coastal, estuarine, and riverine habitats, disproportionately affecting endemic species (Dulvy et al. 2014, freshwater species (Lucifora et al. 2015), and hence, near shore nursery areas (Cuevas-Gómez et al. 2020). ...
... 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 . ...
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.
... Second to (but in addition to) overfishing, habitat loss and degradation resulting from coastal development, agriculture/aquaculture (such as mangrove destruction for shrimp farming), and indirectly through climate (Roff et al. 2016a) has been flagged as a threat for sharks and rays, jeopardizing over onethird (31.2%) of threatened species (Dulvy et al. 2014. This threat is particularly acute in coastal, estuarine, and riverine habitats, disproportionately affecting endemic species (Dulvy et al. 2014, freshwater species (Lucifora et al. 2015), and hence, near shore nursery areas (Cuevas-Gómez et al. 2020). ...
... 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 . ...
Article
Full-text available
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.
... Unmanaged fisheries and trade have resulted in declines of their populations worldwide (Dulvy et al., 2016;Kyne et al., 2020). As keystone species (Bornatowski et al., 2014), elasmobranchs are crucial marine ecological elements structuring food webs and regulating predator-prey behaviour as apex predators (Dulvy et al., 2017;Roff et al., 2016;Heithaus et al., 2008). Trophic downgrading (Estes et al., 2011) by depleting these species may result in altered ecosystem functioning through meso-predatory species release (Stevens et al., 2000;Heithaus et al., 2012;Grubbs et al., 2016), shifting of food web dynamics (Wallach et al., 2015) and thus unsettling the ecological balance. ...
Article
Trade in elasmobranch products is a circum-global practice negatively impacting elasmobranch populations. Although Asia is at the centre of the shark fin trade, countries like Bangladesh, remain data-poor regarding trade dynamics. In the Bay of Bengal region, Bangladesh has a long-standing history of producing and trading products from vulnerable and protected elasmobranchs both nationally and internationally. A limited understanding of trade currently precludes Bangladesh from enforcing regulations effectively and taking timely conservation actions. To address this knowledge gap, we characterized elasmobranch trade by identifying stakeholders involved in national and international trade, routes used, trade hubs, and ports in Bangladesh. We found that most of the trade remains unreported and violates the Wildlife (Conservation and Security) Act, 2012 and CITES mandates. We identified the south-eastern region as a trade hub with a syndicate of traders annually exporting elasmobranch products predominantly to China via Myanmar. High-quality fins and dried meat drive international trade, including products from Critically Endangered sawfish (Pristidae), guitarfishes (Glaucostegidae, Rhinobatidae), wedgefishes (Rhinidae), hammerhead sharks (Sphyrnidae), and large requiem sharks (Carcharhinidae). Also prevalent is a substantial national demand for elasmobranchs for consumption and traditional medicinal uses. Apart from limited alternatives, a low efficiency of acquiring maximum profits in trading other fishery products, an inequality of profit sharing and limited awareness of laws amongst traders results in their non-compliance towards the Wildlife Act, 2012. Along with amendments to this national Act, it is essential to protect threatened species beyond just legal regimes. Enhanced monitoring and inclusive policies are essential for disincentivizing traders to trade such products.
... showing that it may not be necessary to use two different primer pairs to detect those important species (Roff et al., 2016). The performance of teleo agrees with previous analyses (Bylemans et al., 2018b), but contrasts with a recent comparison across multiple primers developed for fishes (Zhang et al., 2020). ...
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Through the development of environmental DNA (eDNA) metabarcoding, in situ monitoring of organisms is becoming easier and promises a revolution in our approaches to detect changes in biodiversity over space and time. A cornerstone of eDNA approach is the development of primer pairs that allow amplifying the DNA of specific taxonomic groups, which is then used to link the DNA sequence to taxonomic identification. Here, we propose a framework for comparing primer pairs regarding (a) their capacity to bind and amplify a broad coverage of species within the target clade using in silico PCR, (b) their capacity to not only discriminate between species but also genera or families, and (c) their in situ specificity and efficiency across a variety of environments. As a case study, we focus on two mitochondrial 12S primer pairs, MiFish-U and teleo, which were designed to amplify fishes. We found that the performance of in silico PCRs were high for both primer pairs, but teleo amplified more genera across Actinopterygii, Chondrichthyes, and Petromyzontomorphi than MiFish-U. In contrast, the discriminatory power for species, genera, and families were higher for MiFish-U than teleo, likely associated with the greater length of the amplified DNA fragments. The evaluation of their in situ efficiency showed a higher recovered species richness of teleo compared to MiFish-U in tropical and temperate freshwater environments, but that generally both teleo and MiFish-U primers pairs perform well to monitor fish species. Since more species were detected when used together, those primer pairs are best used in combination to increase the ability of species detection.
... In this context, the application of the PA to fisheries management and species conservation is not simple or well defined but may prove adequate and useful for elasmobranchs [19,20]. The group of elasmobranchs (sharks, rays, and skates) is an important component of the environment [21,22]. As part of the overall marine biodiversity, these species contribute to the control of prey populations, as well as the overall stability and recovery of marine habitats [23][24][25][26]. ...
Article
This study examined the integration and application of the precautionary principle at national level for the conservation and management of elasmobranchs. Three countries, Greece, Malta, and Cyprus were assessed. Based on national legislation, policies, and reports, the assessment shows limited integration and application of the precautionary approach for the conservation and management of this group. The review of existing measures and relevant literature revealed potential applications of the precautionary principle for two model species, the blue shark (Prionace glauca) and the bull ray (Aetomylaeus bovinus). Sixteen measures, ranging from basic to strong precautionary actions, are proposed to aid the conservation and management of these two species.
... Sharks were categorised as apex sharks or reef sharks according to Roff et al. (2016). Although the fork length of mesopredatory teleosts was measured using EventMeasure software, this measurement did not necessarily occur in the same frame when each of the behaviours of mesopredatory species were recorded. ...
Article
Determining influences of predation and competition on community dynamics is particularly challenging in coral reef systems where interspecific interactions between many predator and prey species play out in patchy landscapes. We used ~1000 stereo-baited remote underwater video deployments (stereo-BRUVs) to assess the relative abundance and analysed the behaviour of two size classes of mesopredatory teleosts (lutajnids, ser-ranids, lethrinids) in the presence and absence of larger predators (mesopredatory and apex carcharhinids). For mesopredatory teleosts, the presence of sharks did not influence the abundance, time of arrival in vicinity of the stereo-BRUVs, the probability of feeding on bait or the delay to feeding. Instead, the number of similar-sized competitors and surrounding habitat features were the strongest drivers of these behavioural metrics. We suggest that for most fishes, the predatory threat posed by highly mobile species such as sharks is likely to be sporadic and transitory, whereas competition is ubiquitous and ever present, particularly for schooling taxa. Ultimately, it is likely that both processes interact to determine behavioural phenotypes as individuals that are inferior competitors can be displaced from safe habitats or prohibited from access to resources and will be more susceptible to predation. Future studies should consider the relative effects of both processes and the degree to which each can be shaped by habitat when investigating trophic dynamics that regulate marine communities.
... Thus, although it is known that batoids regulate populations of some invertebrates and fishes Frisk, 2010;Roff et al., 2016), there is a lack of comprehensive analysis of trophic niche variations in these species, making the prediction of ecological consequences due to changes in their abundance a major challenge (Werner & Gilliam, 1984). Therefore, the objective of this study was to contribute to the overall understanding of the trophic niche of batoids with distribution in Mexican waters through a literature meta-analysis to build capacity for predicting changes in food webs due to anthropogenic impacts or environmental changes. ...
Article
Batoid (rays and skates) populations are declining worldwide, with unknown ecological consequences due to lacking consolidated data on the trophic ecology of these species. Such trends are particularly disconcerting in Mexican waters, where batoids are heavily exploited by commercial fisheries. To assess the current state of knowledge of batoid diet in this region, we conducted a meta-analysis of 54 published stomach content analysis studies. Trophic niche was assessed from 44 total species, including variations due to sex, ontogeny, season, and region, as well as trophic overlap among species. The species assessed belonged to the taxonomic families Urotrygonidae, Dasyatidae, Potamotrygonidae, Mobulidae, Rhinopteridae, Aetobatidae, Gymnuridae, Rhinobatidae, Rajidae, Arhyncobatidae, and Narcinidae. Most of the diet studies to date were conducted in the Mexican Pacific (n = 24), whereas only three studies have come from the Mexican Atlantic, with 27 additional studies coming from other American countries from the tropical and subtropical region. Crustaceans were reported in more than 50% of the species assessed and were also generally the most important prey item, with either high (76%–100%) and medium-high (51%–75%) importance based on dietary indices from the literature reviewed. While the diet of 40 species (91%) consisted of more than one prey type, feeding strategy analysis (Levin and Shannon–Wiener indices) of 27 species indicated that 25 were specialists and two generalists. Species diets varied with ontogeny (20%), sex (11%), region (11%), and seasonality (9%). According to the reviewed studies, interspecific diet overlap was evident in 36% of species, mainly in the family Urotrygonidae. Batoids were grouped into four trophic guilds: crustacivores (68.1%), annelidivores (primarily polychaetes) (13.6%), molluscivores (11.3%), and piscivores (6.8%), based on the literature reviewed. This study showed that most of the batoids had a specialist crustacean-based diet. Future research should focus on species devoid of dietary data to encapsulate the trophic niche breadth of this group in Mexican waters, particularly from the Mexican Atlantic and surrounding regions.
... 3).Sharks are cartilaginous fish of the Class Chondrichthyes and are mostly top predators in the ocean food chain (Fahmi and Dharmadi 2013). Sharks play an important role in maintaining the stability of the food chain through their predation on other organisms (Roff et al. 2016;Heupel et al. 2014). Therefore, it is important to manage shark populations sustainably, especially in areas such as Lombok which are known to be hotspots for shark fisheries (Sembiring et al. 2015). ...
Article
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Environmental DNA (eDNA) metabarcoding is an evolving tool that can provide broader assessments of marine biodiversity than conventional visual census methods. The outputs of this approach are, therefore, crucial to provide data for conservation priorities and to support fisheries management. We conducted a study using eDNA metabarcoding to understand the distribution of marine biodiversity across Indonesia and to investigate the abundance of three major phyla that comprise a majority of marine biodiversity. In this study, a total of 13,819,634 reads corresponding to 23,252 unique sequences belonging to the phyla Chordata, Mollusca, and Echinodermata were generated from COI amplicons obtained from 92 seawater eDNA samples collected from nine locations and 17 sites. Beta diversity differed significantly across locations (PERMANOVA: p < 0.05) based on Bray–Curtis and Jaccard indices. Taxa of interest were not distributed equally and there were no discernible patterns detected across the sampling area. This might be due to the highly variable percentage of sequenced species between families, preventing robust estimation of species richness. Overall, 45% of reads were identified to species level while 55% were classified as unidentified taxa. Interestingly, the percentage of unidentified taxa was similar between two locations with distinct characteristics representing eastern and western extremities of the sampling region. Despite a relatively poor rate of assignment to species level, our results highlight unprecedented levels of marine biodiversity and strong differences in species composition. This further supports the contention that the eDNA approach is a sensitive method that can provide useful data, in particular to detect changes in species composition. Importantly, this method is clearly advantageous to evaluate marine biodiversity on a large scale and can provide data to support region-wide coral reef management strategies. Knowing species diversity and the degree to which various taxa are distributed is a fundamental for advancing our knowledge of marine ecology and can play an important role in forecasting population dynamics and evolution as well as in refining conservation practices.
... Although occasional, small sharks were observed at all reefs, including the gray reef shark (Carcharhinus amblyrhynchos), whitetip reef sharks (Triaenodon obesus), and blacktip reef sharks (Carcharhinus melanopterus). The presence of top predators in the reef environment is critical for the resilience of these ecosystems (Roff et al., 2016), and fishing activities focused on these species can quickly collapse local shark populations over a short period (Heupel et al., 2009). Along the surveyed area, fishermen were observed throwing chunks of red meat to the sea, suggesting a directed fishing practice targeting sharks in the region. ...
Article
Mozambique has the third-largest coastline in the western Indian Ocean with a large and diverse reef area. Those reefs provide food and income for a large proportion of coastal communities but remain scarcely studied. As a baseline assessment, we sampled four uncharted shallow reefs (Baixo Africa, Baixo Zambia, Pomene and Baixo Silvia) within a 56 km stretch line from 5 to 32 meters deep. The fish abundance and assemblage composition were assessed by underwater visual census (25x2m, n = 112). The benthic community was characterized by digital images (0.5x0.5m, n = 164) and the invertebrate megafauna by direct counting (25x2m, n = 52). A total of 209 reef fish species was observed, with similar mean richness (22.4 ± 7.2 species.100 m⁻²) at all reefs. Invertivorous (n = 79) and planktivorous fish species (n = 36) represented 55% of species total. Trophic composition was similar among sites and with large contribution of planktivores. The presence of large shoals (>100 ind.100 m⁻², e.g., surgeonfish, fusiliers, snappers) and large-bodied fishes (>90 cm) (e.g., groupers) was a clear indication of local productivity and health conditions of reefs. Seventy-nine taxa were observed on the benthic cover with the largest richness found at Baixo Silvia (28.5 ± 7.4, species.100m ⁻², mean ±SD). Turf algae dominated the benthos (31.5% ± 16.4) at all sampled reefs. Coral cover was variable between sites (9.3 – 25.8%), dominated by branching and plate corals, and <1% of colonies showed signs of diseases/bleaching. The baseline assessment indicated large biomass of fishes and negligible evidence of large impacts on coral formations which indicated a good conservation status of those areas. Based on these findings, a marine protected area is proposed for establishment in collaboration with environmental authorities and the local community.
... Declines in elasmobranch populations related to diverse and continuous anthropic impacts have been widely reported in the ecosystems of several parts of the world [1][2][3][4]. These losses represent only a fraction of the actual damage suffered by populations in these ecosystems, where elasmobranchs represent important components of the food web [5][6][7][8]. Fishery impacts are also underestimated, given the scarcity of data for most marine ecosystems, particularly in tropical waters and off the coasts of developing countries, with numerous unmonitored fishing communities associated with small-scale fisheries [9]. The growing popular appeal of the conservation of marine environments, the public demand to establish the extent of environmental changes, and the worsening of the conservation status of several flagship species of elasmobranchs have promoted the growth of sustainable management plans in the last decades. ...
Article
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Elasmobranchs represent a group of species under considerable anthropic pressure because of the scale of industrial and artisanal fisheries and the loss of essential areas for nursery and feeding, which are causing substantial population losses around the world. Reproduction in an ex situ environment enables a healthy population to be built and maintained in networks of public aquariums, increasing our knowledge of elasmobranch reproductive biology and offering the opportunity for reintroductions in areas where native populations have been removed. The study reports two successful pregnancies of the whitetip reef shark Triaenodon obesus, considered a vulnerable species by the International Union for the Conservation of Nature. Copulation and gestation data are provided, including ultrasound recordings of the late stage of embryo development. Ultrasonography was performed with the GE Logiq and convex transducer and revealed a fetus with defined fins and organogenesis, with definition of eyes, gills, liver, a heart with individualized chambers, partially defined kidneys, and a well-defined spiral intestine. A cartilaginous skeleton forming a posterior acoustic shadow was detailed, as well as a moving fetus with a biparietal diameter of 6.47 cm and a heart rate of 62 Beats Per Minute on spectral Doppler. This is the first successful reproduction of T. obesus in an aquarium in Brazil.
... white Carcharodon carcharias tiger Galeocerdo cuvier, and bull sharks Carcharhinus leucas 7,8 ). Various ancillary species also incur collateral mortalities as bycatch from the above and other commercial fishing [9][10][11] . ...
Article
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Increasing fishing effort, including bycatch and discard practices, are impacting marine biodiversity, particularly among slow-to-reproduce taxa such as elasmobranchs, and specifically sharks. While some fisheries involving sharks are sustainably managed, collateral mortalities continue, contributing towards > 35% of species being threatened with extinction. To effectively manage shark stocks, life-history information, including resource use and feeding ecologies is pivotal, especially among those species with wide-ranging distributions. Two cosmopolitan sharks bycaught off eastern Australia are the common blacktip shark (Carcharhinus limbatus; globally classified as Near Threatened) and great hammerhead (Sphyrna mokarran; Critically Endangered). We opportunistically sampled the digestive tracts of these two species (and also any whole prey; termed the ‘Russian-doll’ approach), caught in bather-protection gillnets off northern New South Wales, to investigate the capacity for DNA metabarcoding to simultaneously determine predator and prey regional feeding ecologies. While sample sizes were small, S. mokkaran fed predominantly on stingrays and skates (Myliobatiformes and Rajiformes), but also teleosts, while C. limbatus mostly consumed teleosts. Metabarcoding assays showed extensive intermixing of taxa from the digestive tracts of predators and their whole prey, likely via the predator’s stomach chyme, negating the opportunity to distinguish between primary and secondary predation. This Russian-doll effect requires further investigation in DNA metabarcoding studies focussing on dietary preferences and implies that any outcomes will need to be interpreted concomitant with traditional visual approaches.
... For example, multiple studies have demonstrated the ability of predators in upper trophic levels (i.e., fishes) to influence food webs through top-down control (Carpenter et al., 2001;Hansson et al., 2007;Jeppesen et al., 2003). Nevertheless, while this concept has been found to operate in relatively simple ecosystems, such as lakes, recent work in more diverse aquatic ecosystems have not found similar patterns (Casey et al., 2017;Desbiens et al., 2021;Grubbs et al., 2016;Malakhoff & Miller, 2021;Rizzari et al., 2015;Roff et al., 2016). Part of this may be the complexity (i.e., functional diversity) of the predators. ...
Article
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Piscivory is a key ecological function in aquatic ecosystems, mediating energy flow within trophic networks. However, our understanding of the nature of piscivory is limited; we currently lack an empirical assessment of the dynamics of prey capture and how this differs between piscivores. We therefore conducted aquarium‐based performance experiments, to test the feeding abilities of 19 piscivorous fish species. We quantified their feeding morphology, striking, capturing, and processing behavior. We identify two major functional groups: grabbers and engulfers. Grabbers are characterized by horizontal, long‐distance strikes, capturing their prey tailfirst and subsequently processing their prey using their oral jaw teeth. Engulfers strike from short distances, from high angles above or below their prey, engulfing their prey and swallowing their prey whole. Based on a meta‐analysis of 2,209 published in situ predator–prey relationships in marine and freshwater aquatic environments, we show resource partitioning between grabbers. Our results provide a functional classification for piscivorous fishes delineating patterns, which transcend habitats, that may help explain size structures in fish communities. We identify functional groups of piscivorous fishes based on their ability to strike at, capture, and process prey. Also, we show that these groups reflect resource partitioning in aquatic habitats.
... Given there are >1,200 species of sharks and rays, ranging in size from 20 cm to 18 m, that occur in all of the world's oceans, the diversity of predation effects are high and cross many trophic levels (Cortés, 1999;Hussey et al., 2011). While these trophic roles are often difficult to quantify, there is little doubt that sharks function as key predators in a variety of ecosystems and that their removal can have substantial consequences for ecosystem functioning (Ferretti et al., 2010;Roff et al., 2016), including causing trophic cascades (Rasher et al., 2017). Highly mobile sharks also function as energy links between often disparate ecosystems (Heupel et al., 2015;Williams et al., 2018) meaning the consequences of even localized shark population declines may be felt over large spatial scales. ...
Article
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Human-wildlife conflicts are a growing phenomenon globally as human populations expand and wildlife interactions become more commonplace. While these conflicts have been well-defined in terrestrial systems, marine forms are less well-understood. As concerns grow for the future of many shark species it is becoming clear that a key to conservation success lies in changing human behaviors in relation to sharks. However, human-shark conflicts are multidimensional, each with different ecological, social and economic implications. Sharks have functional roles as occasional predators of humans and competitors with humans for fish stocks. In addition, and unlike most terrestrial predators, sharks are also important prey species for humans, being a source of animal protein and other products taken in fisheries. These functional roles are complex and often inter-dependent which can lead to multiple kinds of conflict. Shark management for conservation and human safety is also leading to conflict between different groups of people with different values and beliefs, demonstrating that human wildlife conflict can be a proxy for human-human conflict in the marine domain. Sharks are iconic species in society, being both feared and revered. As such human beliefs, attitudes and perceptions play key roles that underpin much human-shark conflict and future work to understanding these will contribute significantly to solutions that reduce conflict and hence improve conservation outcomes.
... The relative abundance of the piscivores, mostly represented by sharks, could be related to the remarkably diverse teleostean assemblage of the Bolca deposits . It is important to note that all shark species of Bolca are relatively small (less than 200 cm) and presumably did not represent apex predators but instead functioned as meso-predators (see Roff et al. 2016) along with some of the largest teleosts and rays. Feeders on benthic soft prey are represented at Monte Postale site by the narcinid electric ray Titanonarke, and possibly by the urolophid Arechia. ...
Article
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Over the last few years, the morphology, taxonomy and systematics of the cartilaginous fish taxa of the two main sites of the Bolca Lagerstätte, Italy, (Pesciara and Monte Postale sites) have been extensively discussed in a series of papers, resulting in a complete revision of this neglected component of the Eocene Tethyan ichthyofauna. Here, we provide a comprehensive overview of the diversity, palaeoecology and palaeoenvironmental significance of the two chondrichthyan assemblages of the Pesciara and Monte Postale sites. The assemblages include 14 shark species (Lamniformes and Carcharhiniformes) and batoids (Torpediniformes, Rhinopristiformes, Myliobatiformes, Platyrhinidae and Zanobatidae), as well as a single putative chimaeriform. The Pesciara and Monte Postale sites are characterized by eight chondrichthyan taxa each, but the taxonomic compositions are distinctly different reflecting the dissimilarities in the overall composition of both fish assemblages. Palaeoecological interpretations and habitat preferences of the two chondrichthyan assemblages are consistent with previously hypothesized palaeoenvironmental settings based on sedimentological, palaeontological and geochemical evidence. The chondrichthyan assemblages of the two sites appear to be constituted by ecologically vicariant taxa, with both characterized by a predominance of benthic species with durophagous/cancritrophic feeding modes. Taxonomic composition, habitat preferences and palaeobathymetric analyses support the hypothesis that both assemblages occupied tropical marine shallow waters (likely up to 50 m deep) of the inner portion of the Lessini Shelf. The taxonomic composition of both sites is considerably different from that of any other contemporaneous Tethyan and Boreal chondrichthyan assemblages.
... En este sentido, un estudio dirigido a evaluar la mortalidad del sábalo a corto plazo, (< 6 horas) después de su liberación, siguiendo esta modalidad de pesca en Florida (USA), indicó una mortalidad estimada del 5,3 % no asociada a la depredación por tiburones (mortalidad del 13 % si se incluye la depredación por tiburones) (Guindon, 2011). Adicionalmente, la especie tiene una elevada importancia ecológica al ser un mesodepredador, posición vital y altamente comprometida en las redes tróficas costeras (e.g., Roff et al., 2016). ...
Article
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Resumen El sábalo Megalops atlanticus es una especie importante en la pesca recreativa y está evaluada como Vulnerable por la Unión Internacional para la Conservación de la Naturaleza, debido a la sobrepesca y pérdida de sus hábitats. Es abundante en Cuba, capturado en pesquerías comerciales y de subsistencia como fuente de alimento, y comercializado en la pesca recrea-tiva de captura y liberación desarrollada en áreas marinas protegidas. A pesar de su valor pesquero, se desconoce su ecología y estado de conservación en Cuba, lo cual resulta vital para entender el contexto regional en el que se desarrolla la especie. La importancia del sába-lo y los vacíos de conocimiento existentes motivaron el diseño de un proyecto investigativo dirigido a evaluar el uso del hábitat y necesidades de conservación del sábalo en Cuba. En este se propone al Parque Nacional Caguanes (PNC) como una de las áreas de estudio. El PNC presenta potenciales hábitats de crianza para el sábalo, se caracteriza por intensos pe-riodos de sequía alternados por inundaciones, y fue recientemente impactado por eventos meteorológicos extremos (Huracán Irma en 2017 y Tormenta Tropical Alberto en 2018) que afectaron notablemente al manglar. Se han capturado sábalos juveniles en el PNC, para estudios de conectividad entre hábitats en Cuba. En el área no se realiza pesca recreativa de captura y liberación, pero se propone incluir esta modalidad como alternativa de turismo sostenible. Esta propuesta podría ser una experiencia exitosa de manejo, basado en la ciencia, y en una colaboración que contribuye a la conservación.
... In the last few years, the main focus of fish predation studies on coral reefs has been on trophic cascades [10][11][12][13], its effects on prey abundance [14,15], or indirect "fear-effects" on prey behaviour [16][17][18][19]. The fish predators investigated in these fields were primarily sharks or other large mesopredators. ...
Article
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Ecosystem processes are challenging to quantify at a community level, particularly within complex ecosystems (e.g., rainforests, coral reefs). Predation is one of the most important types of species interactions, determining several ecosystem processes. However, while it is widely recognised, it is rarely quantified, especially in aquatic systems. To address these issues, we model predation on fish by fish, in a hyperdiverse coral reef community. We show that body sizes previously examined in fish-fish predation studies (based on a metanalysis), only represent about 5% of likely predation events. The average fish predator on coral reefs is just 3.65 cm; the average fish prey just 1.5 cm. These results call for a shift in the way we view fish predation and its ability to shape the species or functional composition of coral reef fish communities. Considered from a functional group approach, we found general agreement in the distribution of simulated and observed predation events, among both predator and prey functional groups. Predation on coral reefs is a process driven by small fish, most of which are neither seen nor quantified.
... Most of the apex predators in oceans are elasmobranchs, especially sharks, which are renowned for maintaining the energy dynamics, community structure and stability of marine ecosystems through their predatory foraging Roff et al., 2016). These ecological functions may, however, be undermined in the future if ocean acidification disrupts biomineralization and adversely affects the mechanical (e.g. ...
Article
Ocean acidification can cause dissolution of calcium carbonate minerals in biologi- cal structures of many marine organisms, which can be exacerbated by warming. However, it is still unclear whether this also affects organisms that have body parts made of calcium phosphate minerals (e.g. shark teeth), which may also be impacted by the ‘corrosive’ effect of acidified seawater. Thus, we examined the effect of ocean acidification and warming on the mechanical properties of shark teeth (Port Jackson shark, Heterodontus portusjacksoni), and assessed whether their mineralogical proper- ties can be modified in response to predicted near-future seawater pH (–0.3 units) and temperature (+3°C) changes. We found that warming resulted in the production of more brittle teeth (higher elastic modulus and lower mechanical resilience) that were more vulnerable to physical damage. Yet, when combined with ocean acidifica- tion, the durability of teeth increased (i.e. less prone to physical damage due to the production of more elastic teeth) so that they did not differ from those raised under ambient conditions. The teeth were chiefly made of fluorapatite (Ca5(PO4)3F), with in- creased fluoride content under ocean acidification that was associated with increased crystallinity. The increased precipitation of this highly insoluble mineral under ocean acidification suggests that the sharks could modulate and enhance biomineralization to produce teeth which are more resistant to corrosion. This adaptive mineralogical adjustment could allow some shark species to maintain durability and functionality of their teeth, which underpins a fundamental component of predation and sustenance of the trophic dynamics of future oceans.
... amblyrhynchos, T. obesus, C. melanopterus) and apex sharks (G. cuvier, C. plumbeus) based onRoff et al. (2016). ...
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.
... Sharks in modern reefs are well-known to feed on a variety of prey that occupy a range of trophic levels (Hussey et al., 2015;Bond et al., 2018), which means that they do not often occupy the highest trophic position in an ecosystem (Roopnarine and Dineen, 2018). Isotopic evidence confirms that while true apex predatory sharks may occupy high trophic levels, many reef sharks are mesopredators that occupy a similar trophic position to carnivorous bony fish (Roff et al., 2016), a result that is also recovered in the Aptian stage studied here. Thus, the MMR might also represent a significant rise of powerful mesopredators that play an important role in moderating trophic structure. ...
Article
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Ecosystem structure—that is the species present, the functions they represent, and how those functions interact—is an important determinant of community stability. This in turn affects how ecosystems respond to natural and anthropogenic crises, and whether species or the ecological functions that they represent are able to persist. Here we use fossil data from museum collections, literature, and the Paleobiology Database to reconstruct trophic networks of Tethyan paleocommunities from the Anisian and Carnian (Triassic), Bathonian (Jurassic), and Aptian (Cretaceous) stages, and compare these to a previously reconstructed trophic network from a modern Jamaican reef community. We generated model food webs consistent with functional structure and taxon richnesses of communities, and compared distributions of guild level parameters among communities, to assess the effect of the Mesozoic Marine Revolution on ecosystem dynamics. We found that the trophic space of communities expanded from the Anisian to the Aptian, but this pattern was not monotonic. We also found that trophic position for a given guild was subject to variation depending on what other guilds were present in that stage. The Bathonian showed the lowest degree of trophic omnivory by top consumers among all Mesozoic networks, and was dominated by longer food chains. In contrast, the Aptian network displayed a greater degree of short food chains and trophic omnivory that we attribute to the presence of large predatory guilds, such as sharks and bony fish. Interestingly, the modern Jamaican community appeared to have a higher proportion of long chains, as was the case in the Bathonian. Overall, results indicate that trophic structure is highly dependent on the taxa and ecological functions present, primary production experienced by the community, and activity of top consumers. Results from this study point to a need to better understand trophic position when planning restoration activities because a community may be so altered by human activity that restoring a species or its interactions may no longer be possible, and alternatives must be considered to restore an important function. Further work may also focus on elucidating the precise roles of top consumers in moderating network structure and community stability.
... Many shark and ray species are also found associated with coral reefs, with sharks being considered the apex predators of coral reefs as well as fulfilling many other trophic roles (Roff et al., 2016). Similarly, Indonesian waters are reported to contain 109 species of shark, 96 batoids (rays) and 2 ghost sharks (Fahmi* and Dharmadi, 2012). ...
Technical Report
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Southeast Asia is an area of rich marine biodiversity providing a host of ecosystem services that contribute to the well-being of coastal communities and beyond. Sustainable management of ecosystems and the services they provide requires a good understanding of their underlying ecological functions and processes. This understanding can be gained through the rigorous assessment of studies identifying and quantifying ecological functions and ecosystem services. The aims of this study were to review the ecosystem services provided by marine and coastal habitats in Southeast Asia. The ecosystem service potential was scored for each habitat. The review was focused on nine key marine and coastal habitats, identified across four case study sites in Southeast Asia, contributing 18 marine relevant ecosystem services. The approach comprised a literature review supplemented with observations from experts from the case study areas. The four case study sites consist of three Man and Biosphere Reserves in Southeast Asia: Palawan in the Philippines, Cu Lao Cham- Hoi An in Viet Nam, Take-Bonerate Kepulauan Selayar in Indonesia, and a recently gazetted marine protected area, the Tun Mustapha Marine Park in Malaysia. The nine key habitats (eight benthic and one pelagic) covered in this review, identified as highly relevant for most case study sites, were mangrove forests, coral reefs, seagrass meadows, sand, mud, rock, coarse substratum, pelagic and modified habitats. Further division of these habitats into sub-habitats on the basis of biological type and substrate type was used to capture data on differential provision of ecosystem services within the broad habitat types.
... At regional levels, declining trends in populations have also been documented for stingray (family Dasyatidae) stocks in the Arabian Sea with declines of 55% from their historical maximum catch [4,5]. This overwhelming trend in shark and ray population declines is alarming considering these animals serve diverse functions in aquatic ecosystems [6][7][8]. At the other end of the spectrum, sharks and rays are often a source of livelihood, food security, and cultural identity for many coastal communities, and contribute to national economies through fisheries and trade [9][10][11]. ...
Article
Overfishing is recognized as the most pervasive threat to sharks and rays globally. While there is increasing emphasis on ecological aspects of shark and ray fisheries, socio-economic considerations are often poorly incorporated into management policies. Here, we assess the utilization and trade of sharks and rays across the Andaman Islands by conducting semi-structured interviews with 87 fishers and eight traders. Sharks and rays were exported to supply the meat market in peninsular India and contribute to the international trade in products such as fins, gill plates, and liver oil. A large proportion of fishers (n = 38, 43.67%) consumed sharks and rays due to declines in reef fish, as an accessible and cheap protein source. Small-sized sharks (<1 m total length), juvenile hammerheads, and uniformly coloured rays were preferred for local consumption. Fishers (n = 43, 49.42%) noted the difficulty of relying on profits from shark fishing due to declines in shark populations. However, it was easier to fish and trade rays due to their perceived abundance, few regulations, and increased demand for their products. Traders (n = 7, 87.5%) mentioned a rising demand for ray meat from peninsular India, leading to the development of a targeted ray fishery. Expanding and targeted shark and ray fisheries benefit the stakeholders who have the resources to invest, while affecting the livelihoods of others due to declining local fisheries resources. Our results highlight the need to revise and improve legal frameworks to consider the conservation needs of threatened species and likely impacts on local communities.
... (Blaber, 2009) Sementara, hal tersebut dapat mengganggu jaring-jaring makanan dan aliran energi di ekosistem terumbu karang di laut. (Roff, 2016) Permasalahan lingkungan hidup bersifat transnasional yaitu suatu negara yang mengalami kerusakan lingkungan akan memberikan dampak di negara lain yang wilayahnya berdekatan seperti masalah kebakaran hutan. Salah satu contohnya adalah kebakaran hutan di wilayah kalimantan yang menyebabkan penerbangan ke Singapura dibatalkan akibat kendala asap. ...
Article
This study aims to examine the role and position of international environmental institutions in environmental management. Environmental issues are international issues that have a broad effect, involving the exploitation of global resources such as the oceans and atmosphere, as well as the existence of transnational environmental destruction. The United Nations Environment Program (UNEP) is a United Nations (UN) environmental agency that specifically deals with global environmental problems by actively promoting the enforcement of sustainable development in the world. The research method used in this paper is a descriptive analysis method with a historical approach and a conceptual approach. The results of this study indicate that the United Nations through UNEP is able to emphasize government policies in environmental protection programs globally.
... Scalloped hammerheads [Sphyrna lewini (Griffith & Smith, 1834)] are large apex predators with a worldwide distribution, but they are generally found in warm temperate and tropical seas (Roff et al., 2016;Wells et al., 2018;Ebert et al., 2021). Scalloped hammerheads are seasonally migratory and are often observed in large schools (Klimley et al., 1988;Ebert et al., 2021). ...
Article
Major shifts in habitat often occur during life history and can have significant impacts on the morphology and function of an animal; however, little is known about how such ecological changes influence the locomotor system of large aquatic vertebrates. Scalloped hammerheads (Sphyrna lewini) are large sharks found in warm temperate and tropical waters. Smaller scalloped hammerheads are generally found in near-shore habitats, but as they grow larger, individuals spend time in deep-water, pelagic habitats. We measured a number of morphological traits of scalloped hammerheads, ranging from 32 to 130 cm, to determine whether there are allometric changes in morphology in association with this shift in habitat. We found that head morphology, caudal fin area and lateral span scaled with negative allometry, whereas the lengths of their pectoral, dorsal and caudal fins, and their pectoral and caudal fin aspect ratios, scaled with positive allometry. Furthermore, the largest shark in our dataset exhibited an optimal body fineness ratio for locomotor efficiency. This suggests that the changes in ecology have profound influences on the functional morphology of scalloped hammerheads. We discuss how these drastic morphological changes relate to potential changes in scalloped hammerhead swimming function and performance.
... The great hammerhead Sphyrna mokarran (Rüppell, 1837) is a large bodied, coastalpelagic and semi-oceanic shark (Compagno, 1984) with a circumtropical range. It is an uppertrophic level consumer, primarily feeding on other sharks and rays (Raoult et al., 2019) and likely plays an important ecological role in the ecosystems it inhabits (Roff et al., 2016). The life history traits of S. mokarran are characterized by relatively slow growth rates and low fecundity, with biennial parturition and an average litter size of 15 pups (Miller et al., 2014). ...
Article
The great hammerhead (Sphyrna mokarran) is a highly mobile, large‐bodied shark primarily found in coastal‐pelagic and semi‐oceanic waters across a circumtropical range. It is a target or bycatch species in multiple fisheries, and as a result, rapid population declines have occurred in many regions. These declines have contributed to the species being assessed as globally Critically Endangered on the IUCN Red List. While conservation and management measures have yielded promising results in some regions, such as the United States, high levels of at‐vessel and post‐release mortality remain a major concern to the species population recovery. We examined the vertical space use and thermal range of Pop‐Off Archival Satellite tagged S. mokarran in the western North Atlantic Ocean, expanding our understanding of the ecological niche of this species and providing insight into bycatch mitigation strategies for fisheries managers. Our results showed that S. mokarran predominantly used shallow depths (75% of records < 30 m) and have a narrow temperature range (89% of records between 23 and 28 °C). Individual differences in depth use were apparent and a strong diel cycle was observed, with sharks occupying significantly deeper depths during the daytime. Furthermore, two individuals were confirmed pregnant with one migrating from the Bahamas to South Carolina, USA providing further evidence of regional connectivity and parturition off the U.S. east coast. Our findings suggest that S. mokarran may be vulnerable to incidental capture in the western North Atlantic commercial longline fisheries due to substantial vertical overlap between the species and the gear. Our results can be incorporated into conservation and management efforts to develop and/or refine mitigation measures focused on reducing the bycatch and associated mortality of this species, which can ultimately aide S. mokarran population recovery in areas with poor conservation status.
... These species are primarily coastal carcharhiniform sharks in the Families Carcharhinidae and Triakidae, which are the dominant sharks landed in tropical and temperate coastal fisheries, respectively (Yokota & Lessa, 2006;Walker, 2007;Carlson et al., 2012;Yates et al., 2015). Carcharhinids and triakids fulfill ecological roles as mid-level and apex predators in these ecosystems, suggesting that broader ecological effects may be initiated when they are removed Roff et al., 2016). Some of the most highly traded cosmopolitan pelagic species are prohibited or restricted from landings in RMFOs and listed on Appendix II of CITES. ...
Article
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One third of chondrichthyan species (sharks, rays, and chimeras) are threatened with extinction, mainly due to unsustainable fishing. Large accessible international markets for meat and luxury products like dried fins can help drive overfishing by encouraging targeted capture or retention of high-value export species. If this is common, then species in international trade could have heightened extinction risk. Here, we examined the species composition of the Hong Kong shark fin market from 2014 to 2018, finding that traded species disproportionately occur in threatened categories (70.9%) and all premium value species are threatened. A small number of cosmopolitan species dominate the trade, but noncosmopolitan coastal species are still traded at concerning levels given their limited distribution. These coastal species are not generally subject to retention prohibitions, fisheries management, or international trade regulations and without management many could become extinct. The conservation potential of international trade regulations alone for coastal chondrichthyans depends on the extent to which overfishing is driven by export markets; socioeconomic studies of coastal fishing communities are needed to make this determination. Nonetheless , adding international trade regulations for more coastal shark species that are in the fin trade could prompt broad engagement with overfishing in nations lacking effective management. K E Y W O R D S CITES, governance, Hong Kong, international shark trade, management, shark conservation This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
... The extinction and reintroduction of gray wolves in Yellowstone National Park are examples of drastic changes in top predator populations that affect the entire ecosystem (Ripple and Beschta, 2012). Similar instances can be enumerated not only in terrestrial but also in marine ecosystems (Myers et al., 2007;Baum and Worm, 2009;Roff et al., 2016). ...
Article
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The Yokozuna Slickhead Narcetes shonanmaruae is a recently described deep-sea fish species and an active-swimming, relatively large top predator in Suruga Bay, Japan. Its only known habitat is the deepest part of the bay (>2,000 m); six individuals have been collected thus far (up to 138 cm in total length). During our monitoring survey of faunal diversity on seamounts within marine protected areas in Japanese waters, environmental DNA (eDNA) metabarcoding revealed the Yokozuna Slickhead 12S ribosomal RNA gene sequence on/around three seamounts belonging to the Nishi-Shichito Ridge (at depths of around 2,000 m) located 400–600 km south of the known locality. A baited camera system deployed at the foot of one of the three seamounts at a depth of 2,091 m captured a Yokozuna Slickhead individual that was over 250 cm in total length, threatening Pacific Grenadiers Coryphaenoides acrolepis around the bait and attacking the bait cage. A combination of eDNA metabarcoding and baited camera observation represents a powerful tool for the detection of rare predatory fish species and the study of their ecology even in the deep sea, thus helping to better understand vulnerable marine ecosystems and reveal the impact of the rapidly changing global ocean.
... Although deterrent efficacy was not 100%, there is an inherent need for an eco-friendly cost-effective approach to shark-human shoreline coexistence since shark culling/mitigation measures in areas, such as South Africa [46], Australia [47], and Réunion Island [17] persist. Continued research efforts demonstrate the importance of sharks in relation to their respective ecosystems [48,49], and therefore, continued larger-scale research on this novel technology on various potentially dangerous shark species (e.g., white sharks-Carcharodon carcharias; tiger sharks-Galeocerdo cuvier) in varying ecological conditions (e.g., high wave activity and strong currents) is warranted. Lastly, insufficient evidence has been presented on the behavioral effects of permanent and electromagnet shark deterrent technologies on teleost, mammalian, or chelonian species. ...
Article
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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.
... Scalloped hammerheads [Sphyrna lewini (Griffith & Smith, 1834)] are large apex predators with a worldwide distribution, but they are generally found in warm temperate and tropical seas (Roff et al., 2016;Wells et al., 2018;Ebert et al., 2021). Scalloped hammerheads are seasonally migratory and are often observed in large schools (Klimley et al., 1988;Ebert et al., 2021). ...
Article
Major shifts in habitat often occur during life history and can have significant impacts on the morphology and function of an animal; however, little is known about how such ecological changes influence the locomotor system of large aquatic vertebrates. Scalloped hammerheads (Sphyrna lewini) are large sharks found in warm temperate and tropical waters. Smaller scalloped hammerheads are generally found in near-shore habitats, but as they grow larger, individuals spend time in deep-water, pelagic habitats. We measured a number of morphological traits of scalloped hammerheads, ranging from 32 to 130 cm, to determine whether there are allometric changes in morphology in association with this shift in habitat. We found that head morphology, caudal fin area and lateral span scaled with negative allometry, whereas the lengths of their pectoral, dorsal and caudal fins, and their pectoral and caudal fin aspect ratios, scaled with positive allometry. Furthermore, the largest shark in our dataset exhibited an optimal body fineness ratio for locomotor efficiency. This suggests that the changes in ecology have profound influences on the functional morphology of scalloped hammerheads. We discuss how these drastic morphological changes relate to potential changes in scalloped hammerhead swimming function and performance.
... In terrestrial and marine ecological systems, top-order predators act to shape trophic structures below them [1][2][3]. Coral reefs provide ecosystem services to top predators, and predatory fishes play an important role in overall ecosystem function and health [4,5]. Predator species influence prey behaviour and remove prey items from ecosystems, regulating the composition of, and dynamics within prey assemblages [6,7]. ...
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.
... It may be that this large loss in biomass is caused by a few species with large body sizes, such as sharks, groupers, and jacks, that contribute greatly to biomass but less to total species richness (MacNeil et al 2020, McClanahan et al 2021b. The consequences of these losses for ecological function and yield may be important but are not well understood (Roff et al 2016). ...
Article
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Negative trade-offs between food production and biodiversity and the positive functional diversity–productivity relationships are potentially conflicting paradigms that are frequently evoked in conservation and sustainability science and management. While the complementary niches of species could potentially increase fisheries yields, stark food-diversity trade-offs have been proposed for wild-caught fisheries. Nevertheless, this first evaluation of stock biomass, yields, and species relationships in 115 coral reef locations in the Western Indian Ocean found that management for multispecies-maximum sustained yield (MMSY) will increase both food production and numbers of species relative to open access fisheries. A precipitous loss of >50% of species did not occur until >70% of the fishable and target biomasses was depleted. At MMSY, 6%–15% of total predicted number of fish species were lost indicating a need for other conservation mechanisms. These patterns occurred because the best-fit to the yield-numbers of species relationship was either a saturation or convex parabolic relationship. Fishing at MMSY in coral reefs should provide considerable diversity required to support many ecosystem services. Low biomass and overfishing were common and around 80% of studied locations were losing ∼2.0–2.5 tons km⁻² yr⁻¹ and 15%–40% of their species relative to MMSY.
... Understanding the ecological roles and importance of large-bodied aquatic consumers (particularly high trophic level predators) has been the focus of an increasing number of studies over the past two decades, including marine mammals, sharks, sea turtles, seabirds, and crocodilians (e.g., Katona and Whitehead, 1988;Bowen, 1997;Heithaus et al., 2008;Heithaus, 2013;Roman et al., 2014;Kiszka et al., 2015;Estes et al., 2016;Roff et al., 2016;Somaweera et al., 2020). While these studies and reviews have demonstrated that species within each of these taxa may play important roles, both as predators and prey, it is becoming increasingly apparent that there is a need to better understand the diversity of functional roles predators have in aquatic ecosystems, the pathways through which they might affect the structure and function of biological communities and ecosystems, and the contexts in which species may be more or less important. ...
Article
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Small cetaceans (dolphins, porpoises, and small toothed whales) occur from the poles to the tropics, and from freshwater habitats to the open ocean. Most ecological research has focused on the influence of abiotic factors on the abundance, distribution, and behavior of these species. The ecological impacts of small cetaceans on communities and ecosystems remain poorly quantified. Their movement patterns, often high local and regional abundances across a range of ecosystems, and high metabolic rates suggest that small cetaceans could have large effects on ecosystem structure, dynamics, and function through a variety of mechanisms. These include top-down (e.g., direct predation and risk effects) and bottom-up effects (e.g., translocation of nutrients within and across ecosystems), but also behavior-mediated processes where these predators can facilitate access to resources to other predators or modify the physical properties of habitat (e.g., bioturbation). Most small cetaceans can be consumed by other marine predators, particularly killer whales (Orcinus orca) and large sharks. Although consumption rates of small cetaceans can be high, there is a paucity of information on their effects on population sizes or behaviors of their prey. Mass-balance ecosystem models suggest that small cetaceans may impact the populations of short-lived prey species (particularly fish and cephalopods), but other factors (e.g., eutrophication and fisheries) also affect ecosystem functioning and population trends. Delphinids can also mediate the translocation and recycling of limiting nutrients between spatially distinct ecosystems on a diel basis. Despite intriguing possibilities, large gaps remain in our understanding of the roles and importance of small cetaceans in aquatic ecosystems, both marine and freshwater.
... En este sentido, un estudio dirigido a evaluar la mortalidad del sábalo a corto plazo, (< 6 horas) después de su liberación, siguiendo esta modalidad de pesca en Florida (USA), indicó una mortalidad estimada del 5,3 % no asociada a la depredación por tiburones (mortalidad del 13 % si se incluye la depredación por tiburones) (Guindon, 2011). Adicionalmente, la especie tiene una elevada importancia ecológica al ser un mesodepredador, posición vital y altamente comprometida en las redes tróficas costeras (e.g., Roff et al., 2016). ...
Article
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Resumen El sábalo Megalops atlanticus es una especie importante en la pesca recreativa y está evaluada como Vulnerable por la Unión Internacional para la Conservación de la Naturaleza, debido a la sobrepesca y pérdida de sus hábitats. Es abundante en Cuba, capturado en pesquerías comerciales y de subsistencia como fuente de alimento, y comercializado en la pesca recrea-tiva de captura y liberación desarrollada en áreas marinas protegidas. A pesar de su valor pesquero, se desconoce su ecología y estado de conservación en Cuba, lo cual resulta vital para entender el contexto regional en el que se desarrolla la especie. La importancia del sába-lo y los vacíos de conocimiento existentes motivaron el diseño de un proyecto investigativo dirigido a evaluar el uso del hábitat y necesidades de conservación del sábalo en Cuba. En este se propone al Parque Nacional Caguanes (PNC) como una de las áreas de estudio. El PNC presenta potenciales hábitats de crianza para el sábalo, se caracteriza por intensos pe-riodos de sequía alternados por inundaciones, y fue recientemente impactado por eventos meteorológicos extremos (Huracán Irma en 2017 y Tormenta Tropical Alberto en 2018) que afectaron notablemente al manglar. Se han capturado sábalos juveniles en el PNC, para estudios de conectividad entre hábitats en Cuba. En el área no se realiza pesca recreativa de captura y liberación, pero se propone incluir esta modalidad como alternativa de turismo sostenible. Esta propuesta podría ser una experiencia exitosa de manejo, basado en la ciencia, y en una colaboración que contribuye a la conservación.
Article
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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.
Article
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Large sharks generally occupy the highest trophic levels and are important links in the structuring of trophic networks. However, the decline of these predators has been observed worldwide, with population reduction rates reaching over 90% for some species. Through these declines, it is believed that the effect of the loss of predators could result in the disturbances in ecosystems. Based on this, the present study aimed to test the role of elasmobranchs in a coastal ecosystem in southern Brazil. Also, we tested if the changes in fishing effort cause changes in trophic structure. For this, a trophodynamic model was performed, based on reliable data on biomass and species feeding in the region. The mass balance modeling software Ecopath with Ecosim (EwE) was used to assess the trophic position of sharks and rays, and to understand what their interactions are with other groups in the ecosystem. Among the parameters of the model, the Paraná coast showed to be an immature system, with high connectivity and medium complexity. The trophic levels of the coast varied from 1 to 4.4, with level > 4 composed of sharks, and rays belonging to the third trophic level. Sharks were strong impacted by fishing. According to changes in fishing effort simulations, we observed changes of intermediate levels due to the decline of large sharks. However, no cascade effects were observed from the simulations. The high diversity of the system, feeding overlap, and the redundancy between mesopredator and other teleosts can decrease the chances of a cascade effect occurring.
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Coral reef ecosystems are exceptionally complex with a myriad of trophic pathways and consumer relationships. The application of stable isotopes (SIs) offers numerous advantages over traditional methods towards understanding these intricate systems. We summarize current knowledge derived from the rapidly increasing SI literature base and identify potential gaps and future directions for the use of SI in coral reef ecosystem studies. Using topic modelling, a form of text mining, on 236 identified published works, we determined that SI research on coral reefs broadly falls into five major topics. 1) Organic matter dynamics: SI analyses (SIA) have quantified substantial variability in autochthonous (internal) and allochthonous (external) fluxes across coral reefs. 2) Holobiont metabolism: Coral nutrient acquisition, translocation and partitioning, and coral responses to various endogenous and exogenous factors, have been explored through SIA. 3) Trophic niches: SIA has indicated that considerable variation in resource use facilitates co-occurrence of high densities of consumers, emphasising that many trophic categorisations on reefs are often too simplistic. 4) Fish diet variation and habitat connectivity: SIA has revealed how ontogenetic, larval, and mobile predator movements link adjacent ecosystems. 5) Environmental drivers (both natural and anthropogenic): SIA can track anthropogenic nutrient inputs, revealing impacts of human-derived pollutants on reef systems. There are a number of important knowledge gaps however. Few studies compare feeding strategies across guilds and the literature is biased towards reef fish and hard corals. Furthermore, few studies examine multiple taxonomic groups in situ or consider multiple environmental drivers. Studies also tend to ignore the underlying, but potentially substantial, spatiotemporal variation in SI baselines as demonstrated from 741 mean SI values extracted from the literature, making inferences based on small variations in SI values problematic. Given that coral reefs face global decline, knowledge gaps need to be addressed while acknowledging the limitations of SIA; careful application of SIs can enhance understanding of processes driving environmental change in these iconic marine ecosystems.
Article
Localised stressors compound the ongoing climate‐driven decline of coral reefs, requiring natural resource managers to work within rapidly shifting paradigms. Trait‐based adaptive management (TBAM) is a new framework to help address changing conditions by choosing and implementing management actions specific to species groups that share key traits, vulnerabilities, and management responses. TBAM balances maintenance of functioning ecosystems with provisioning for human subsistence and livelihoods. We first identified trait‐based groups of food fish in a Pacific coral reef with hierarchical clustering. Positing that trait‐based groups performing comparable functions respond similarly to both stressors and management actions, we ascertained biophysical and socio‐economic drivers of trait‐group biomass and evaluated their vulnerabilities with generalised additive models. Clustering identified seven trait groups from 131 species. Groups responded to different drivers and displayed divergent vulnerabilities, with human activities emerging as important predictors of community structuring. Biomass of small, solitary reef‐associated species increased with distance from key fishing ports, and large, solitary piscivores exhibited a decline in biomass with distance from a port. Group biomass also varied in response to different habitat types, the presence or absence of reported dynamite fishing activity and wave energy exposure. The differential vulnerabilities of trait groups reveal how food fish community structure is driven by different aspects of resource use and habitat. This inherent variability in the responses of trait‐based groups presents opportunities to apply selective trait‐based adaptive management strategies for complex, multi‐species fisheries. This approach can be widely adjusted to suit local contexts and priorities. This article is protected by copyright. All rights reserved
Article
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.
Article
Elasmobranchs play a significant role in structuring the marine food webs in many marine habitats. Estuaries provide an essential habitat primarily as nurseries for elasmobranchs. The present study investigates the feeding preferences of megabenthic predatory elasmobranchs from Caranzalem Bay, Goa. The elasmobranchs in this habitat were represented by guitarfishes, Glaucostegus granulatus and Glaucostegus obtusus; rays, Brevitrygon walga, Pastinachus sephen, Neotrygon kuhlii, and Maculabatis gerrardi; and bamboo sharks, Chiloscyllium griseum and Chiloscyllium spp. Crustaceans were the major prey of these predators followed by teleosts and cephalopods. The bamboo shark was an opportunistic predator while rays and guitarfish were specialised feeders on penaeid shrimps. Indices suggest that bamboo sharks occupy the highest trophic level in this benthic food chain while guitarfishes and rays function as mesopredators. Ontogenetic dietary changes were observed in all predators, indicating the feeding niche segregation among size classes. Low resource overlap was observed between and within species probably due to high prey availability in the bay. These elasmobranch species frequently occur in bycatch, which can negatively affect their populations and thereby impact the lower trophic strata resulting in large-scale ecological repercussions.
Preprint
Increased rates of species extirpation or extinction have often been attributed to the foraging behavior of invasive predators, with drastic effects on native food webs. In the Caribbean, the invasive red lionfish ( Pterois volitans ) is of primary concern, as it reduces the overall recruitment and biomass of reef fishes by as much as 80% and 65%, respectively. Understanding the functional role that this predator plays in the context of entire communities is critical to assessing how it impacts those that have already experienced regime shifts due to disturbance. Here, a trait-based ecospace was employed to characterize the functional role of red lionfish trophic behavior, focusing on a regional pool of reef fishes from Jamaica, Cuba, and the Cayman Islands. A high-resolution model of a Greater Antilles coral reef food web, including micro- and macrobiota, producers and consumers, and invertebrates and vertebrates, was used to assess the impacts of P. volitans on community structural parameters such as food chain length, the number of interactions, modularity, and trophic position. Results indicate that lionfish select prey based on specific traits, foraging primarily on those that are diurnal, below a threshold of total length, occur higher in the water column, do not possess a physical defense, and are either herbivorous, invertivorous, or omnivorous. The functional role of lionfish significantly overlaps with a number of endemic high trophic level predators, such as Rhizoprionodon porosus , Negaprion brevirostris , and Scomberomorus regalis . Lionfish could be fulfilling trophic roles previously vacated by extirpated species, as the prey of the lionfish were found to be functionally indiscriminate relative to those of extirpated predators such as Sphyrna tiburo , Carcharhinus acronotus , and Galeocerdo cuvier . In addition, food web results suggest that lionfish alter the trophic dynamics of the entire reef community by increasing the total number of interactions and changing trophic level structure. Interestingly, the invasive lionfish may be restoring and augmenting some effects of predation otherwise lost to species extirpation, providing an alternative view to its detrimental effects on resilience of Caribbean marine systems.
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Changes in the type and prevalence of human diseases have occurred during shifts in human social organization, for example, from hunting and gathering to agriculture and with urbanization during the Industrial Revolution. The recent emergence and reemergence of infectious diseases appears to be driven by globalization and ecological disruption. We propose that habitat destruction and biodiversity loss associated with biotic homogenization can increase the incidence and distribution of infectious diseases affecting humans. The clearest connection between biotic homogenization and infectious disease is the spread of nonindigenous vectors and pathogens. The loss of predators and hosts that dilute pathogen transmission can also increase the incidence of vectorborne illnesses. Other mechanisms include enhanced abiotic conditions for pathogens and vectors and higher host-pathogen encounter rates. Improved understanding of these causal mechanisms can inform decisionmaking on biodiversity conservation as an effective way to protect human health.
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