Individual and Population Benefits of Marine Reserves for Reef Sharks

The Sharklogger Network-monitoring Cayman Islands shark populations through an innovative citizen science program

The use of citizen science can be a cost-effective tool in conservation science but mostly relies on the collation of incidental sighting reports. This study describes the design, operation, and findings of a novel, closely-guided citizen science program (the 'Sharklogger Network') in the Cayman Islands. Participants from the recreational SCUBA diving community used a standardized, effort-based protocol to monitor local coastal shark populations. Over two years (2017-2018) a total of 69 participants conducted 24,442 dives across 472 dives sites and recorded 4,666 shark sightings from eight shark species, of which Caribbean reef shark, nurse shark, and hammerhead spp. were the most frequently observed and encountered throughout the year. The data from dive logs provided evidence for species-specific distribution and abundance patterns across and within islands, indicating a greater abundance of sharks in areas with less anthropogenic activity and with a greater exposure to strong currents, regardless of whether the area was an MPA or not. While both Caribbean reef sharks and nurse sharks showed species-specific depth and habitat preferences, the recording of recognizable individuals showed that some individuals of both species have relatively small home ranges and high site-fidelity to specific areas. The study also provided the first confirmation of reproductive behaviour in both Caribbean reef and nurse sharks taking place in summer (May-August). Experience showed that along with generating valuable data the program, by engaging local stakeholders, also enhanced public awareness of shark conservation issues. This study demonstrates that this citizen science methodology can be an affordable and non-invasive tool for the reliable long-term monitoring of shark populations.

Where giants roam: The importance of remote islands and seamount corridors to adult tiger sharks in the South Pacific Ocean

The movements of tiger sharks (Galeocerdo cuvier) across their global distribution are diverse and complex, and there remains a dearth of information about the cues that influence migrations of adults to and from offshore islands. We aimed to delineate broad-scale movements of a seasonally abundant tiger shark aggregation at Norfolk Island, a remote small island in the South Pacific Ocean, by identifying migratory pathways and important areas, as well as quantifying the association between space use and environmental factors. We satellite tracked 35 tiger sharks, consisting of some of the largest individuals ever monitored (median total length: 4.0 m), between February 2020 and April 2023. Tracking periods averaging 305 days (14 - 686 days) showed movements throughout large parts of the South Pacific Ocean including near New Caledonia, the Great Barrier Reef, Papua New Guinea, Chesterfield Islands, Vanuatu, Fiji, and New Zealand. The longest track was close to 17,000 km over 468 days. There was high seasonal fidelity to Norfolk Island with 88% of sharks tracked across multiple seasons returning at least once, mainly from New Caledonia. The median date of arrival and departure from Norfolk Island were in December and May, respectively. Coastal use of islands was the most important factor across monthly habitat suitability models, whereas sea surface temperature explained seasonal departures/arrivals from/to Norfolk Island. The findings of our study show diverse potential movement trajectories and cues used by tiger sharks, but importantly highlight the critical role of Norfolk Island and other nearshore areas in supporting large adult female tiger sharks.

Predator removals, trophic cascades and outbreaks of crown-of-thorns starfish on coral reefs

The removal of mesopredatory fishes by fishing may be a key factor driving outbreaks of crown-of-thorns starfish on coral reefs. Evidence for this idea has been derived from correlations between starfish densities and fishing pressure. However, dietary analyses using DNA, studies of the trophic role of mesopredatory fishes and experiments that have invoked threat responses suggest that outbreaks could also result from a trophic cascade driven, in part, by changes in the anti-predator behaviours of these fishes. If corroborated, this hypothesis could inform management decision-making, slowing the frequency of outbreaks and improving the health of coral reefs in the Anthropocene.

Shallow seamounts are "oases" and activity hubs for pelagic predators in a large-scale marine reserve

Seamounts have been likened to "oases" of life in the comparative deserts of the open ocean, often harbouring high densities of threatened and exploited pelagic top predators. However, few such aggregations have been studied in any detail and the mechanisms that sustain them are poorly understood. Here, we present the findings of an integrated study of 3 previously unexplored seamounts in the tropical Atlantic, which aimed to investigate their significance as predator "hotspots" and inform their inclusion in one of world's largest marine reserves. Baited underwater video and visual census transects revealed enhanced diversity and biomass of pelagic top predators, including elevated abundances of 7 species of sharks, predatory fish, and seabirds, within 5 km of 2 shallow seamounts (<100 m), but not a third deeper seamount (260 m). Hydroacoustic biomass of low- and mid-trophic level "prey" was also significantly elevated within 2.5 km of shallow seamounts. However, we found no evidence of enhanced primary productivity over any feature, suggesting high faunal biomass is sustained by exogenous energy inputs. Relative biomass enrichment also increased with trophic level, ranging from a 2-fold increase for zooplankton to a 41-fold increase for sharks. Tracking of the dominant predator species revealed that individual sharks (Galapagos, silky) and tuna (yellowfin, bigeye) often resided around seamounts for months to years, with evidence of connectivity between features, and (in the case of sharks) were spatially aggregated in localised hotspots that coincided with areas of high mid-trophic biomass. However, tuna and silky sharks also appeared to use seamounts as "hubs" in more extensive pelagic foraging ranges, which may help explain disproportionately high predator density. Our results reinforce the conservation significance of shallow seamounts for many marine top predators and offer fundamental insights into their functional roles as both prey "oases" and activity hubs for these species.

Evaluating the influence of marine protected areas on surf zone fish

Marine protected areas (MPAs) globally serve conservation and fisheries management goals, generating positive effects in some marine ecosystems. Surf zones and sandy beaches, critical ecotones bridging land and sea, play a pivotal role in the life cycles of numerous fish species and serve as prime areas for subsistence and recreational fishing. Despite their significance, these areas remain understudied when evaluating the effects of MPAs. We compared surf zone fish assemblages inside and outside MPAs across 3 bioregions in California (USA). Using seines and baited remote underwater videos (BRUVs), we found differences in surf zone fish inside and outside MPAs in one region. Inside south region MPAs, we observed higher abundance (Tukey's honest significant difference [HSD] = 0.83, p = 0.0001) and richness (HSD = 0.22, p = 0.0001) in BRUVs and greater biomass (HSD = 0.32, p = 0.0002) in seine surveys compared with reference sites. Selected live-bearing, fished taxa were positively affected by MPAs. Elasmobranchs displayed greater abundance in BRUV surveys and higher biomass in seine surveys inside south region MPAs (HSD = 0.35, p = 0.0003 and HSD = 0.23, p = 0.008, respectively). Although we observed no overall MPA signal for Embiotocidae, abundances of juvenile and large adult barred surfperch (Amphistichus argenteus), the most abundant fished species, were higher inside MPAs (K-S test D = 0.19, p < 0.0001). Influence of habitat characteristics on MPA performance indicated surf zone width was positively associated with fish abundance and biomass but negatively associated with richness. The south region had the largest positive effect size on all MPA performance metrics. Our findings underscored the variability in species richness and composition across regions and survey methods that significantly affected differences observed inside and outside MPAs. A comprehensive assessment of MPA performance should consider specific taxa, their distribution, and the effects of habitat factors and geography.

Directed conservation of the world's reef sharks and rays

Many shark populations are in decline around the world, with severe ecological and economic consequences. Fisheries management and marine protected areas (MPAs) have both been heralded as solutions. However, the effectiveness of MPAs alone is questionable, particularly for globally threatened sharks and rays ('elasmobranchs'), with little known about how fisheries management and MPAs interact to conserve these species. Here we use a dedicated global survey of coral reef elasmobranchs to assess 66 fully protected areas embedded within a range of fisheries management regimes across 36 countries. We show that conservation benefits were primarily for reef-associated sharks, which were twice as abundant in fully protected areas compared with areas open to fishing. Conservation benefits were greatest in large protected areas that incorporate distinct reefs. However, the same benefits were not evident for rays or wide-ranging sharks that are both economically and ecologically important while also threatened with extinction. We show that conservation benefits from fully protected areas are close to doubled when embedded within areas of effective fisheries management, highlighting the importance of a mixed management approach of both effective fisheries management and well-designed fully protected areas to conserve tropical elasmobranch assemblages globally.

The essential habitat role of a unique coastal inlet for a widely distributed apex predator

Essential habitats support specific functions for species, such as reproduction, feeding or refuge. For highly mobile aquatic species, identifying essential habitats within the wider distribution range is central to understanding species ecology, and underpinning effective management plans. This study examined the movement and space use patterns of sevengill sharks (Notorynchus cepedianus) in Caleta Valdés (CV), a unique coastal habitat in northern Patagonia, Argentina. Seasonal residency patterns of sharks were evident, with higher detectability in late spring and early summer and lower during autumn and winter. The overlap between the residency patterns of sharks and their prey, elephant seals, suggests that CV functions as a seasonal feeding aggregation site for N. cepedianus. The study also found sexual differences in movement behaviour, with males performing abrupt departures from CV and showing increased roaming with the presence of more sharks, and maximum detection probability at high tide. These movements could be related to different feeding strategies between sexes or mate-searching behaviour, suggesting that CV may also be essential for reproduction. Overall, this study highlights the importance of coastal sites as essential habitats for N. cepedianus and deepens our understanding of the ecological role of this apex predator in marine ecosystems.

Quantifying longline bycatch mortality for pelagic sharks in western Pacific shark sanctuaries

Marine protected areas are increasingly touted for their role in conserving large marine predators such as sharks, but their efficacy is debated. Seventeen "shark sanctuaries" have been established globally, but longline fishing continues within many such jurisdictions, leading to unknown levels of bycatch mortality levels. Using public data from Global Fishing Watch and Regional Fisheries Management Organizations, we quantified longline fishing within eight shark sanctuaries and estimated pelagic shark catch and mortality for seven pelagic shark species. Sanctuary mortality ranged from 600 individuals (Samoa) to 36,256 individuals (Federated States of Micronesia), equivalent to ~5% of hypothesized sustainable levels for blue sharks to ~40% for silky sharks, with high mortality levels in the Federated States of Micronesia, Palau, and the Marshall Islands. Unsustainable mortality rates were exceeded for silky sharks in two sanctuaries, highlighting a need for additional stock assessments and implementation of bycatch reduction measures. Big data integration workflows represent a transformative tool in fisheries management, particularly for data-poor species.

Comparing spatial management tools to protect highly migratory shark species in the Eastern Mediterranean Sea hot spots

Bycatch of non-target species is a pressing problem for ocean management. It is one of the most concerning issues related to human-wildlife interactions and it affects numerous species including sharks, seabirds, sea turtles, and many critically endangered marine mammals. This paper compares different policy tools for ocean closure management around a unique shark aggregation site in Israel's nearshore coastal waters. We provide a set of recommendations based on an optimal management approach that allows humans to enjoy marine recreational activities such as fishing, while maintaining safe conditions for these apex predators which are vital to the local marine ecosystem. To learn more about recreational fishers' derived benefits, we use a benefit transfer method. Our main conclusion is that dynamic time-area closures offer sustainable and effective management strategies. Since these closures are based on near real-time data, they might successfully preserve specific species in limited areas (i.e., small areas).

Habitat-use of the vulnerable Atlantic Nurse Shark: a review

Human activities have led to the loss of critical habitats for aquatic species at such an accelerated rate that habitat modification is considered a leading threat to biodiversity. Sharks and rays are considered the second most threatened group of vertebrates that have also suffered from habitat loss, especially in nursery grounds and reef-associated species. In this sense, actions toward the conservation of critical grounds for species survival are urgently needed, especially for those threatened with extinction. This study aimed to gather and provide information on the worldwide distribution and habitat association of the 'vulnerable' Atlantic Nurse Shark Ginglymostoma cirratum through a literature review performed at the Dimensions research database. A total of 30 studies published between 1950 and 2021 were retained since they defined at least the type of habitat in which G. cirratum was associated. Most studies covered the Floridian ecoregion, where G. cirratum is more common and abundant. Reefs, seagrass, sandy, rocky, mangrove, and macroalgae accounted for the majority of habitat associations, with a higher diversity of habitats detected within marine protected areas (MPAs). Ginglymostoma cirratum was recorded at a maximum depth of 75 m, temperatures ranging from 25 °C to 34 °C, and salinities between 31 and 38 ppt. Neonates were associated with shallower habitats (<20 m), mostly reefs, rocks, macroalgae, sandy shores, and seagrass, in an average temperature of 26 °C and salinity of 36 ppt. Breeding events and habitats were reported by 11 studies, 72.7% of them in shallow waters, mostly inside MPAs (90.9%). Our findings highlighted the key role played by MPAs in protecting essential grounds for threatened species, such as the Atlantic Nurse Shark. Major ecoregions (e.g., the Eastern Atlantic) are still underrepresented in the scientific literature as long as studies aim specifically to assess G. cirratum habitat association. Thus, further insights into the essential habitats needed to conserve the Atlantic Nurse Shark can still emerge from future studies. Considering the recent IUCN extinction risk status change in G. cirratum (i.e., Data Deficient to 'Vulnerable'), new conservation measures that integrate habitat protection and management are urgently needed and should consider the data collected herein.

Behaviour of mesopredatory coral reef fishes in response to threats from sharks and humans

Both sharks and humans present a potentially lethal threat to mesopredatory fishes in coral reef systems, with implications for both population dynamics and the role of mesopredatory fishes in reef ecosystems. This study quantifies the antipredator behaviours mesopredatory fishes exhibit towards the presence of large coral reef carnivores and compares these behavioural responses to those elicited by the presence of snorkelers. Here, we used snorkelers and animated life-size models of the blacktip reef shark (Carcharhinus melanopterus) to simulate potential predatory threats to mesopredatory reef fishes (lethrinids, lutjanids, haemulids and serranids). The responses of these reef fishes to the models and the snorkelers were compared to those generated by three non-threatening controls (life-size models of a green turtle [Chelonia mydas], a PVC-pipe [an object control] and a Perspex shape [a second object control]). A Remote Underwater Stereo-Video System (Stereo-RUV) recorded the approach of the different treatments and controls and allowed accurate measurement of Flight Initiation Distance (FID) and categorization of the type of flight response by fishes. We found that mesopredatory reef fishes had greater FIDs in response to the approach of threatening models (1402 ± 402-1533 ± 171 mm; mean ± SE) compared to the controls (706 ± 151-896 ± 8963 mm). There was no significant difference in FID of mesopredatory fishes between the shark model and the snorkeler, suggesting that these treatments provoked similar levels of predator avoidance behaviour. This has implications for researchers monitoring behaviour in situ or using underwater census as a technique to estimate the abundance of reef fishes. Our study suggests that, irrespective of the degree to which sharks actually consume these mesopredatory reef fishes, they still elicit a predictable and consistent antipredator response that has the potential to create risk effects.

Personality in juvenile Atlantic cod ecotypes and implications for fisheries management

Animals show among-individual variation in behaviors, including migration behaviors, which are often repeatable across time periods and contexts, commonly termed "personality." These behaviors can be correlated, forming a behavioral syndrome. In this study, we assessed the repeatability and correlation of different behavioral traits, i.e., boldness, exploration, and sociality, and the link to feeding migration patterns in Atlantic cod juveniles. To do so, we collected repeated measurements within two short-term (3 days) and two long-term (2 months) intervals of these personality traits and genotypes of the Pan I locus, which is correlated with feeding migration patterns in this species. We found high repeatabilities for exploration behavior in the short- and long-term intervals, and a trend for the relationship between exploration and the Pan I locus. Boldness and sociality were only repeatable in the second short-term interval indicating a possible development of stability over time and did not show a relation with the Pan I locus. We found no indication of behavioral syndromes among the studied traits. We were unable to identify the existence of a migration syndrome for the frontal genotype, which is the reason that the link between personality and migration remains inconclusive, but we demonstrated a possible link between exploration and the Pan I genotype. This supports the need for further research that should focus on the effect of exploration tendency and other personality traits on cod movement, including the migratory (frontal) ecotype to develop management strategies based on behavioral units, rather than treating the population as a single homogeneous stock.

Biologging and Biotelemetry: Tools for Understanding the Lives and Environments of Marine Animals

Addressing important questions in animal ecology, physiology, and environmental science often requires in situ information from wild animals. This difficulty is being overcome by biologging and biotelemetry, or the use of miniaturized animal-borne sensors. Although early studies recorded only simple parameters of animal movement, advanced devices and analytical methods can now provide rich information on individual and group behavior, internal states, and the surrounding environment of free-ranging animals, especially those in marine systems. We summarize the history of technologies used to track marine animals. We then identify seven major research categories of marine biologging and biotelemetry and explain significant achievements, as well as future opportunities. Big data approaches via international collaborations will be key to tackling global environmental issues (e.g., climate change impacts), and curiosity about the secret lives of marine animals will also remain a major driver of biologging and biotelemetry studies.

Conceptual frameworks and key questions for assessing the contribution of marine protected areas to shark and ray conservation

Marine protected areas (MPAs) are key tools in addressing the global decline of sharks and rays, and marine parks and shark sanctuaries of various configurations have been established to conserve shark populations. However, assessments of their efficacy are compromised by inconsistent terminology, lack of standardized approaches to assess how MPAs contribute to shark and ray conservation, and ambiguity about how to integrate movement data in assessment processes. We devised a conceptual framework to standardize key terms (e.g., protection, contribution, potential impact, risk, threat) and used the concept of portfolio risk to identify key attributes of sharks and rays (assets), the threats they face (portfolio risk), and the specific role of MPAs in risk mitigation (insurance). Movement data can be integrated into the process by informing risk exposure and mitigation through MPAs. The framework is operationalized by posing 8 key questions that prompt practitioners to consider the assessment scope, MPA type and purpose, range of existing and potential threats, species biology and ecology, and management and operational contexts. Ultimately, MPA contributions to shark and ray conservation differ according to a complex set of human and natural factors and interactions that should be carefully considered in MPA design, implementation, and evaluation.

Characterization of 35 new microsatellite markers for the blacktip reef shark (Carcharhinus melanopterus) and cross-species amplification in eight other shark species

BACKGROUND

Shark species are overfished at a global scale, as they are poached for the finning industry or are caught as bycatch. Efficient conservation measures require fine-scale spatial and temporal studies to characterize shark habitat use, infer migratory habits, analyze relatedness, and detect population genetic differentiation. Gathering these types of data is costly and time-consuming, especially when it requires collection of shark tissue samples.

METHODS AND RESULTS

Genetic tools, such as microsatellite markers, are the most economical sampling method for collecting genetic data, as they enable the estimation of genetic diversity, population structure and parentage relationships and are thus an efficient way to inform conservation strategies. Here, a set of 45 microsatellite loci was tested on three blacktip reef shark (Carcharhinus melanopterus) populations from three Polynesian islands: Moorea, Morane and Tenararo. The set was composed of 10 previously published microsatellite markers and 35 microsatellite markers that were developed specifically for C. melanopterus as part of the present study. The 35 novel and 10 existing loci were cross-amplified on eight additional shark species (Carcharhinus amblyrhynchos, C. longimanus, C. sorrah, Galeocerdo cuvier, Negaprion acutidens, Prionacea glauca, Rhincodon typus and Sphyrna lewini). These species had an average of 69% of successful amplification, considered if at least 50% of the individual samples being successfully amplified per species and per locus.

CONCLUSIONS

This novel microsatellite marker set will help address numerous knowledge gaps that remain, concerning genetic stock identification, shark behavior and reproduction via parentage analysis.

Half a century of rising extinction risk of coral reef sharks and rays

Sharks and rays are key functional components of coral reef ecosystems, yet many populations of a few species exhibit signs of depletion and local extinctions. The question is whether these declines forewarn of a global extinction crisis. We use IUCN Red List to quantify the status, trajectory, and threats to all coral reef sharks and rays worldwide. Here, we show that nearly two-thirds (59%) of the 134 coral-reef associated shark and ray species are threatened with extinction. Alongside marine mammals, sharks and rays are among the most threatened groups found on coral reefs. Overfishing is the main cause of elevated extinction risk, compounded by climate change and habitat degradation. Risk is greatest for species that are larger-bodied (less resilient and higher trophic level), widely distributed across several national jurisdictions (subject to a patchwork of management), and in nations with greater fishing pressure and weaker governance. Population declines have occurred over more than half a century, with greatest declines prior to 2005. Immediate action through local protections, combined with broad-scale fisheries management and Marine Protected Areas, is required to avoid extinctions and the loss of critical ecosystem function condemning reefs to a loss of shark and ray biodiversity and ecosystem services, limiting livelihoods and food security.

Like a rolling stone: Colonization and migration dynamics of the gray reef shark (Carcharhinus amblyrhynchos)

Designing appropriate management plans requires knowledge of both the dispersal ability and what has shaped the current distribution of the species under consideration. Here, we investigated the evolutionary history of the endangered gray reef shark (Carcharhinus amblyrhynchos) across its range by sequencing thousands of RADseq loci in 173 individuals in the Indo-Pacific (IP). We first bring evidence of the occurrence of a range expansion (RE) originating close to the Indo-Australian Archipelago (IAA) where two stepping-stone waves (east and westward) colonized almost the entire IP. Coalescent modeling additionally highlighted a homogenous connectivity (Nm ~ 10 per generation) throughout the range, and isolation by distance model suggested the absence of barriers to dispersal despite the affinity of C. amblyrhynchos to coral reefs. This coincides with long-distance swims previously recorded, suggesting that the strong genetic structure at the IP scale (F ST ~ 0.56 between its ends) is the consequence of its broad current distribution and organization in a large number of demes. Our results strongly suggest that management plans for the gray reef shark should be designed on a range-wide rather than a local scale due to its continuous genetic structure. We further contrasted these results with those obtained previously for the sympatric but strictly lagoon-associated Carcharhinus melanopterus, known for its restricted dispersal ability. Carcharhinus melanopterus exhibits a similar RE dynamic but is characterized by a stronger genetic structure and a nonhomogeneous connectivity largely dependent on local coral reefs availability. This sheds new light on shark evolution, emphasizing the roles of IAA as source of biodiversity and of life-history traits in shaping the extent of genetic structure and diversity.

Shark Fishing vs. Conservation: Analysis and Synthesis

The expanding shark fin market has resulted in intensive global shark fishing and with 90% of teleost fish stocks over-exploited, sharks have become the most lucrative target. As predators, they have high ecological value, are sensitive to fishing pressure, and are in decline, but the secretive nature of the fin trade and difficulties obtaining relevant data, obscure their true status. In consumer countries, shark fin is a luxury item and rich consumers pay high prices with little interest in sustainability or legal trade. Thus, market demand will continue to fuel the shark hunt and those accessible to fishing fleets are increasingly endangered. Current legal protections are not working, as exemplified by the case of the shortfin mako shark, and claims that sharks can be sustainably fished under these circumstances are shown to be misguided. In the interests of averting a catastrophic collapse across the planet’s aquatic ecosystems, sharks and their habitats must be given effective protection. We recommend that all sharks, chimaeras, manta rays, devil rays, and rhino rays be protected from international trade through an immediate CITES Appendix I listing. However, a binding international agreement for the protection of biodiversity in general is what is needed.

Genomic insights into the historical and contemporary demographics of the grey reef shark

Analyses of genetic diversity can shed light on both the origins of biodiversity hotspots, as well as the conservation status of species that are impacted by human activities. With these objectives, we assembled a genomic dataset of 14,935 single nucleotide polymorphisms from 513 grey reef sharks (Carcharhinus amblyrhynchos) sampled across 17 locations in the tropical Indo-Pacific. We analysed geographic variation in genetic diversity, estimated ancient and contemporary effective population size (N_e) across sampling locations (using coalescent and linkage disequilibrium methods) and modelled the history of gene flow between the Coral Triangle and the Coral Sea. Genetic diversity decreased with distance away from the Coral Triangle and north-western Australia, implying that C. amblyrhynchos may have originated in this region. Increases in N_e were detected across almost all sampling locations 40,000-90,000 generations ago (approximately 0.6-1.5 mya, given an estimated generation time of 16.4 years), suggesting a range expansion around this time. More recent, secondary increases in N_e were inferred for the Misool and North Great Barrier Reef sampling locations, but joint modelling did not clarify whether these were due to population growth, migration, or both. Despite the greater genetic diversity and ancient N_e observed at sites around Australia and the Coral Triangle, remote reefs around north-western New Caledonia had the highest contemporary N_e, demonstrating the importance of using multiple population size assessment methods. This study provides insight into both the past and present demographics of C. amblyrhynchos and contributes to our understanding of evolution in marine biodiversity hotspots.

Conservation implications of forage base requirements of a marine predator population at carrying capacity

Prey depletion may contribute to marine predator declines, yet the forage base required to sustain an unfished population of predatory fish at carrying capacity is unknown. We integrated demographic and physiological data within a Bayesian bioenergetic model to estimate annual consumption of a gray reef shark (Carcharhinus amblyrhynchos) population at a remote Pacific atoll (Palmyra Atoll) that are at carrying capacity. Furthermore, we estimated the proportion of the atoll's reef fish biomass production consumed by the gray reef sharks, assuming sharks either partially foraged pelagically (mean 7%), or solely within the reef environment (mean 52%). We then predicted the gray reef shark population potential of other, less remote Pacific Ocean coral reef islands, illustrating that current populations are substantially smaller than could be supported by their forage base. Our research highlights the utility of modeling how far predator population sizes are from their expected carrying capacity in informing marine conservation.

•

Diet impacts the consumptive influence of gray reef sharks on reef fish resources

•

Some gray reef shark populations could be larger, considering their forage base

•

Modeling potential predator population sizes can inform their conservation

Drivers of variation in occurrence, abundance, and behaviour of sharks on coral reefs

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.

Overfishing drives over one-third of all sharks and rays toward a global extinction crisis

The scale and drivers of marine biodiversity loss are being revealed by the International Union for Conservation of Nature (IUCN) Red List assessment process. We present the first global reassessment of 1,199 species in Class Chondrichthyes-sharks, rays, and chimeras. The first global assessment (in 2014) concluded that one-quarter (24%) of species were threatened. Now, 391 (32.6%) species are threatened with extinction. When this percentage of threat is applied to Data Deficient species, more than one-third (37.5%) of chondrichthyans are estimated to be threatened, with much of this change resulting from new information. Three species are Critically Endangered (Possibly Extinct), representing possibly the first global marine fish extinctions due to overfishing. Consequently, the chondrichthyan extinction rate is potentially 25 extinctions per million species years, comparable to that of terrestrial vertebrates. Overfishing is the universal threat affecting all 391 threatened species and is the sole threat for 67.3% of species and interacts with three other threats for the remaining third: loss and degradation of habitat (31.2% of threatened species), climate change (10.2%), and pollution (6.9%). Species are disproportionately threatened in tropical and subtropical coastal waters. Science-based limits on fishing, effective marine protected areas, and approaches that reduce or eliminate fishing mortality are urgently needed to minimize mortality of threatened species and ensure sustainable catch and trade of others. Immediate action is essential to prevent further extinctions and protect the potential for food security and ecosystem functions provided by this iconic lineage of predators.

Global trends in aquatic animal tracking with acoustic telemetry

Acoustic telemetry (AT) is a rapidly evolving technique used to track the movements of aquatic animals. As the capacity of AT research expands it is important to optimize its relevance to management while still pursuing key ecological questions. A global review of AT literature revealed region-specific research priorities underscoring the breadth of how AT is applied, but collectively demonstrated a lack of management-driven objectives, particularly relating to fisheries, climate change, and protection of species. In addition to the need for more research with direct pertinence to management, AT research should prioritize ongoing efforts to create collaborative opportunities, establish long-term and ecosystem-based monitoring, and utilize technological advancements to bolster aquatic policy and ecological understanding worldwide.

The MPA Guide: A framework to achieve global goals for the ocean

[Figure: see text].

Complete mitochondrial genome of the Caribbean reef shark, Carcharhinus perezi (Carcharhinformes: Carcharhinidae)

The Caribbean reef shark (Carcharhinus perezi; Poey, 1876) is a medium to large-bodied coastal and reef-associated predator found throughout the subtropical and tropical waters of the Atlantic Ocean and Caribbean Sea, although its populations are increasingly threatened by overfishing. We describe the first mitochondrial genome sequence for this species, using Illumina MiSeq sequencing of an individual from The Bahamas. We report the mitogenome sequence of the Caribbean reef shark to be 16,709 bp and composed two rRNA genes, 22 tRNA genes, 13 protein-coding genes, 2 non-coding regions; the D-loop control region and the origin of light-strand replication. We discuss the implications of this new information on future monitoring efforts and conservation measures such as marine protected areas, and urge for greater application of mitochondrial studies of sharks in the Atlantic Ocean.

Nation-wide assessment of the distribution and population size of the data-deficient nurse shark (Ginglymostoma cirratum)

The study presents the first national assessment of a nurse shark (Ginglymostoma cirratum) population, conducted using a combination of transect surveys and baited remote underwater videos (BRUVs). Density of nurse sharks in Belize was found to be higher in reefs than in lagoons, and in the atolls furthest away from the mainland and human settlements. Only large and old protected areas were found to have a positive impact on nurse shark abundance. Absolute abundance of nurse sharks was estimated using distance sampling analysis, giving a total nurse shark population in the range of 3,858 to 14,375 sharks. Thanks to a vast area of suitable habitat for nurse sharks in the country and legislation already in place for the safeguard of the species, Belize could represent an important hotspot for nurse sharks in the Western Atlantic. The data presented here hence offers a baseline for the long-term monitoring of the Belizean nurse shark population and improves our understanding of nurse shark abundance and distribution in the wider Caribbean basin.

International fisheries threaten globally endangered sharks in the Eastern Tropical Pacific Ocean: the case of the Fu Yuan Yu Leng 999 reefer vessel seized within the Galápagos Marine Reserve

Shark fishing, driven by the fin trade, is the primary cause of global shark population declines. Here, we present a case study that exemplifies how industrial fisheries are likely depleting shark populations in the Eastern Tropical Pacific Ocean. In August 2017, the vessel Fu Yuan Yu Leng 999, of Chinese flag, was detained while crossing through the Galápagos Marine Reserve without authorization. This vessel contained 7639 sharks, representing one of the largest seizures recorded to date. Based on a sample of 929 individuals (12%), we found 12 shark species: 9 considered as Vulnerable or higher risk by the IUCN and 8 listed in CITES. Four species showed a higher proportion of immature than mature individuals, whereas size-distribution hints that at least some of the fishing ships associated with the operation may have been using purse-seine gear fishing equipment, which, for some species, goes against international conventions. Our data expose the magnitude of the threat that fishing industries and illegal trade represent to sharks in the Eastern Tropical Pacific Ocean.

Recent expansion of marine protected areas matches with home range of grey reef sharks

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.

Maximizing regional biodiversity requires a mosaic of protection levels

Protected areas are the flagship management tools to secure biodiversity from anthropogenic impacts. However, the extent to which adjacent areas with distinct protection levels host different species numbers and compositions remains uncertain. Here, using reef fishes, European alpine plants, and North American birds, we show that the composition of species in adjacent Strictly Protected, Restricted, and Non-Protected areas is highly dissimilar, whereas the number of species is similar, after controlling for environmental conditions, sample size, and rarity. We find that between 12% and 15% of species are only recorded in Non-Protected areas, suggesting that a non-negligible part of regional biodiversity occurs where human activities are less regulated. For imperiled species, the proportion only recorded in Strictly Protected areas reaches 58% for fishes, 11% for birds, and 7% for plants, highlighting the fundamental and unique role of protected areas and their environmental conditions in biodiversity conservation.

This study shows that the dissimilarity in species composition between sites with different levels of protection is consistently high, suggesting that adjacent and connected areas with different protection levels host very dissimilar species assemblages.

Conservation: Goldilocks Nations for Restoring Reef Sharks

The first baited, video-based global survey of coral reef sharks reveals widespread depletion and functional extinction from eight nations. The authors identify priority 'Goldilocks' nations with the necessary combination of governance and shark abundance to recover depleted shark populations.

Spatially congruent sites of importance for global shark and ray biodiversity

Many important areas identified for conservation priorities focus on areas of high species richness, however, it is unclear whether these areas change depending on what aspect of richness is considered (e.g. evolutionary distinctiveness, endemicity, or threatened species). Furthermore, little is known of the extent of spatial congruency between biodiversity measures in the marine realm. Here, we used the distribution maps of all known marine sharks, rays, and chimaeras (class Chondrichthyes) to examine the extent of spatial congruency across the hotspots of three measures of species richness: total number of species, evolutionarily distinct species, and endemic species. We assessed the spatial congruency between hotspots considering all species, as well as on the subset of the threatened species only. We consider three definitions of hotspot (2.5%, 5%, and 10% of cells with the highest numbers of species) and three levels of spatial resolution (1°, 4°, and 8° grid cells). Overall, we found low congruency among all three measures of species richness, with the threatened species comprising a smaller subset of the overall species patterns irrespective of hotspot definition. Areas of congruency at 1° and 5% richest cells contain over half (64%) of all sharks and rays and occurred off the coasts of: (1) Northern Mexico Gulf of California, (2) USA Gulf of Mexico, (3) Ecuador, (4) Uruguay and southern Brazil, (5) South Africa, southern Mozambique, and southern Namibia, (6) Japan, Taiwan, and parts of southern China, and (7) eastern and western Australia. Coarsening resolution increases congruency two-fold for all species but remains relatively low for threatened measures, and geographic locations of congruent areas also change. Finally, for pairwise comparisons of biodiversity measures, evolutionarily distinct species richness had the highest overlap with total species richness regardless of resolution or definition of hotspot. We suggest that focusing conservation attention solely on areas of high total species richness will not necessarily contribute efforts towards species that are most at risk, nor will it protect other important dimensions of species richness.

Marine Conservation: Reef Sharks Need Bigger Protected Areas

A new study finds that most marine protected areas around coral reefs are too small to protect reef-associated sharks.