Challenges and Priorities in Shark and Ray Conservation

Little Sharks in a Big World: Mitochondrial DNA Reveals Small-scale Population Structure in the California Horn Shark (Heterodontus francisci)

The California horn shark (Heterodontus francisci) is a small demersal species distributed from southern California and the Channel Islands to Baja California and the Gulf of California. These nocturnal reef predators maintain small home-ranges as adults, and lay auger-shaped egg cases that become wedged into the substrate. While population trends are not well documented, this species is subject to fishing pressure through portions of its range and has been identified as vulnerable to overexploitation. Here we present a survey of 318 specimens from across the range, using mtDNA control region sequences to provide the first genetic assessment of H. francisci. Overall population structure (ΦST = 0.266, P < 0.001) is consistent with limited dispersal as indicated by life history, with two distinct features. Population structure along the continuous coastline is low, with no discernable breaks from Santa Barbara, CA to Bahia Tortugas (Baja California Sur, Mexico); however, there is a notable partition at Punta Eugenia (BCS), a well-known biogeographic break between tropical and subtropical marine faunas. In contrast, population structure is much higher (max ΦST = 0.601, P < 0.05) between the coast and adjacent Channel Islands, a minimum distance of 19 km, indicating that horn sharks rarely disperse across deep habitat and open water. Population structure in most elasmobranchs is measured on a scale of hundreds to thousands of kilometers, but the California Horn Shark has population partitions on an unprecedented small scale, indicating a need for localized management strategies which ensure adequate protection of distinct stocks.

Stock Assessment of Four Dominant Shark Bycatch Species in Bottom Trawl Fisheries in the Northern South China Sea

Sharks occupy an important ecological niche in marine ecosystems. As top predators, they can restrict and control the behavior, numbers and composition of other species through downward effects, and play an essential role in ecosystem stability. Shark fishery data are limited, and for most Chondrichthyes species there is no formal fishery resource assessment at a global level. In this study, we applied the length-based Bayesian biomass (LBB) estimation method to assess the stock status of four common shark bycatch species of which more than 100 samples were collected in coastal waters of the northern South China Sea. Estimates of the length of 50% of individuals captured by gear/the length at first capture that maximized the catch and biomass (Lc/Lc_opt) of a species ranged from 0.49 to 1.4; the draughtsboard shark Cephaloscyllium sarawakensis had the highest value, and the shortnose dogfish Squalus brevirostris had the lowest. Estimates of the collected biomass/biomass of the maximum sustainable yield (B/BMSY) ranged from 0.86 to 1.9. Both C. sarawakensis and the spadenose shark Scoliodon laticaudus were fully exploited, while the spatulasnout catshark Apristurus platyrhynchus and S. brevirostris were in good condition. To verify the stability of the LBB, length frequency data for the most common species S. laticaudus were divided into different size-class intervals; simulations revealed estimated parameters based on these to be insensitive to differences in intervals, except for the smallest (10 mm), which did not affect evaluation results. These results can be used to provide a scientific basis on which shark fisheries in this region can be managed and prior parameters for related resource assessment methods can be determined.

Global patterns in functional rarity of marine fish

Rare species, which represent a large fraction of the taxa in ecological assemblages, account for much of the biological diversity on Earth. These species make substantial contributions to ecosystem functioning, and are targets of conservation policy. Here we adopt an integrated approach, combining information on the rarity of species trait combinations, and their spatial restrictedness, to quantify the biogeography of rare fish (a taxon with almost 13,000 species) in the world's oceans. We find concentrations of rarity, in excess of what is predicted by a null expectation, near the coasts and at higher latitudes. We also observe mismatches between these rarity hotspots and marine protected areas. This pattern is repeated for both major groupings of fish, the Actinopterygii (bony fish) and Elasmobranchii (sharks, skates and rays). These results uncover global patterns of rarity that were not apparent from earlier work, and highlight the importance of using metrics that incorporate information on functional traits in the conservation and management of global marine fishes.

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.

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

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

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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.

Net illumination reduces fisheries bycatch, maintains catch value, and increases operational efficiency

Small-scale fisheries are vital for food security, nutrition, and livelihoods in coastal areas throughout the world's oceans.^1-9 As intricately linked social-ecological systems, small-scale fisheries require management approaches that help ensure both ecological and socioeconomic sustainability.^7,10-14 Given their ease of use and lucrative nature, coastal gillnet fisheries are globally ubiquitous.^10,15 However, these fisheries often result in high discarded capture of non-target organisms (bycatch) that can lead to significant cascading effects throughout trophic chains^16-18 and costly fisheries restrictions that result in important revenue losses in coastal communities with scarce economic alternatives.^19,20 Despite these challenges, few solutions have been developed and broadly adopted to decrease bycatch in coastal gillnet fisheries, particularly in developing nations.^5,21 Here we used controlled experiments along Mexico's Baja California peninsula to show that illuminating gillnets with green LED lights-an emerging technology originally developed to mitigate sea turtle bycatch-significantly reduced mean rates of total discarded bycatch biomass by 63%, which included significant decreases in elasmobranch (95%), Humboldt squid (81%), and unwanted finfish (48%). Moreover, illuminated nets significantly reduced the mean time required to retrieve and disentangle nets by 57%. In contrast, there were no significant differences in target fish catch or value. These findings advance our understanding of how artificial illumination affects operational efficiency and changes in catch rates in coastal gillnet fisheries, while illustrating the value of assessing broad-scale ecological and socioeconomic effects of species-specific conservation strategies.

Population and seascape genomics of a critically endangered benthic elasmobranch, the blue skate Dipturus batis

The blue skate (Dipturus batis) has a patchy distribution across the North-East Atlantic Ocean, largely restricted to occidental seas around the British Isles following fisheries-induced population declines and extirpations. The viability of remnant populations remains uncertain and could be impacted by continued fishing and by-catch pressure, and the projected impacts of climate change. We genotyped 503 samples of D. batis, obtained opportunistically from the widest available geographic range, across 6 350 single nucleotide polymorphisms (SNPs) using a reduced-representation sequencing approach. Genotypes were used to assess the species' contemporary population structure, estimate effective population sizes and identify putative signals of selection in relation to environmental variables using a seascape genomics approach. We identified genetic discontinuities between inshore (British Isles) and offshore (Rockall and Faroe Island) populations, with differentiation most pronounced across the deep waters of the Rockall Trough. Effective population sizes were largest in the Celtic Sea and Rockall, but low enough to be of potential conservation concern among Scottish and Faroese sites. Among the 21 candidate SNPs under positive selection was one significantly correlated with environmental variables predicted to be affected by climate change, including bottom temperature, salinity and pH. The paucity of well-annotated elasmobranch genomes precluded us from identifying a putative function for this SNP. Nevertheless, our findings suggest that climate change could inflict a strong selective force upon remnant populations of D. batis, further constraining its already-restricted habitat. Furthermore, the results provide fundamental insights on the distribution, behaviour and evolutionary biology of D. batis in the North-East Atlantic that will be useful for the establishment of conservation actions for this and other critically endangered elasmobranchs.

Insights into genetic variation and demographic history of sharpnose rays: Examinations of three species of Telatrygon (Elasmobranchii, Dasyatidae) from the Indo-West Pacific

Coastal and demersal chondrichthyans (sharks, rays, and skates) are expected to exhibit high levels of genetic differentiation in areas of complex geomorphology. Population genetic studies investigating the extent to which demographic history shapes the genetic structure of these fishes are rare. Here, we combination mitochondrial DNA (Cytb and ND2) and eight nuclear microsatellite loci from 244 individuals to examine the population genetic structure and demographic history of the three Indo-West Pacific species of sharpnose rays (Telatrygon zugei, Telatrygon biasa, and Trygon crozieri). High levels of genetic variation both within and between species was identified. Phylogenetic analysis partitioned haplotypes into two lineages supporting divergence of T. zugei from T. crozieri and T. biasa during the Pleistocene. Furthermore, microsatellite-based clustering analyses identified four genetic groups (i.e., T. zugei from Japan, T. zugei from coastal China, T. biasa from Gulf of Thailand, and T. crozieri from the Andaman Sea. Measurements of genetic differentiation also support these four groups. Additionally, Pleistocene demographic expansions were examined in all genetic groups. The climate oscillations and current hydrologic cycles in the Indo-West Pacific appear to be coincide with the hypothesis regarding speciation and the observed demographic history trends of the sharpnose rays. Considering the species group has, until recently, been thought to be one species, these results are critical for defining management units and guiding conservation efforts to preserve stingray biodiversity. This article is protected by copyright. All rights reserved.

Fish functional diversity as an indicator of resilience to industrial fishing in Patagonia Argentina

The relationship between fish functional diversity and fishing levels at which its baselines shift is important to identify the consequences of fishing in ecosystem functioning. For the first time, the authors of this study implemented a trait-based approach in the Argentine Patagonian Sea to identify the vulnerability and spatiotemporal changes in functional diversity of fish assemblages incidentally captured by a trawling fleet targeting the Argentine red shrimp Pleoticus muelleri (Spence Bate, 1888) between 2003 and 2014. The authors coupled seven fish trophic traits to a reconstructed fish assemblage for the study area and by-catch and evaluated changes in fish species richness and four complementary functional diversity measures (functional richness, redundancy, dispersion and community trait values) along with fishing intensity, temporal use, latitudinal location and depth of fishing grounds, and vessel length. Resident fishes larger than 30 cm in length, with depressed and fusiform bodies, intermediate to high trophic levels, and feeding in benthic, demersal and midwater areas were vulnerable to by-catch. In addition, fish assemblages exhibited a low functional trait redundancy, likely related to species influxes in a biogeographic ecotone with tropicalisation signs. Significant increases in fish trait richness and dispersion poleward and deep suggested new functional roles in these grounds, matching trends in community body size, reproductive load, maximum depth and trophic level. Finally, a temporal increase in fish species and functional trait removal in fishing grounds led to trait homogenisation since 2003. The authors identified that tipping points in temperate fish functional trait diversity showed the importance of trait-based approaches within ecosystem-based fisheries management.

Defining distribution and habitat use of west-central Florida's coastal sharks through a research and education program

Identifying critical habitat for highly mobile species such as sharks is difficult, but essential for effective management and conservation. In regions where baseline data are lacking, non-traditional data sources have the potential to increase observational capacity for species distribution and habitat studies. In this study, a research and education organization conducted a 5-year (2013-2018) survey of shark populations in the coastal waters of west-central Florida, an area where a diverse shark assemblage has been observed but no formal population analyses have been conducted. The objectives of this study were to use boosted regression tree (BRT) modeling to quantify environmental factors impacting the distribution of the shark assemblage, create species distribution maps from the model outputs, and identify spatially explicit hot spots of high shark abundance. A total of 1036 sharks were captured, encompassing eleven species. Abundance hot spots for four species and for immature sharks (collectively) were most often located in areas designated as "No Internal Combustion Engine" zones and seagrass bottom cover, suggesting these environments may be fostering more diverse and abundant populations. The BRT models were fitted for immature sharks and five species where n > 100: the nurse shark (Ginglymostoma cirratum), blacktip shark (Carcharhinus limbatus), blacknose shark (C. acronotus), Atlantic sharpnose shark (Rhizoprionodon terraenovae), and bonnethead (Sphyrna tiburo). Capture data were paired with environmental variables: depth (m), sea surface temperature (°C), surface, middle, and bottom salinity (psu), dissolved oxygen (mg/L), and bottom type (seagrass, artificial reef, or sand). Depth, temperature, and bottom type were most frequently identified as predictors with the greatest marginal effect on shark distribution, underscoring the importance of nearshore seagrass and barrier island habitats to the shark assemblage in this region. This approach demonstrates the potential contribution of unconventional science to effective management and conservation of coastal sharks.

Comparative Study of Semen Parameters and Hormone Profile in Small-Spotted Catshark (Scyliorhinus canicula): Aquarium-Housed vs. Wild-Captured

Simple Summary

Comprehensive knowledge of chondrichthyan reproductive biology is crucial for the development of reproductive technologies. For that reason, a male reproductive evaluation was performed on the basis of a comparison of samples collected from wild-captured and aquarium-housed small-spotted catshark (Scyliorhinus canicula). Semen quality, sperm morphometry, and reproductive hormones were assessed. The results demonstrate good in vitro semen quality in aquarium-housed sharks, although there was lower plasma testosterone.

Abstract

Several chondrichthyan species are threatened, and we must increase our knowledge of their reproductive biology in order to establish assisted reproductive protocols for ex situ or in situ endangered species. The small-spotted catshark (Scyliorhinus canicula) is one of the most abundant shark species of the Mediterranean coast and is easy to maintain in aquaria; therefore, it is considered an ideal reproductive model. This study aimed to compare S. canicula male reproductive function in aquarium-housed (n = 7) and wild-captured animals, recently dead (n = 17). Aquarium-housed animals had lower semen volume (p = 0.005) and total sperm number (p = 0.006) than wild-captured animals, but similar sperm concentrations. In terms of sperm parameters, aquarium-housed sharks showed higher total sperm motility (p = 0.004), but no differences were observed regarding sperm viability, mitochondrial membrane potential, or membrane integrity. A morphometric study pointed to a significantly longer head (p = 0.005) and acrosome (p = 0.001) in wild-captured animals. The results of the spermatozoa morphological study of S. canicula were consistent with previous results obtained in other chondrichthyan species. With regard to sex hormones, testosterone levels were significantly lower in aquarium-housed animals (p ≤ 0.001), while similar levels of 17β-estradiol and progesterone were found. In short, the present study provides evidence of good in vitro semen quality in S. canicula housed in an aquarium, underlining their excellent potential for application in reproductive technologies for this and other chondrichthyan species.

What fisher diets reveal about fish stocks

Tracking fish consumption could provide additional information on changes to fish stocks, one of the planet's main protein sources. We used data on seafood consumption in fishing villages in Brazil over time to test for changes in: species richness, diversity, and composition, fish size and trophic levels, consumption of endangered species, and functional diversity (namely, species with different behavioral and habitat preferences). Our results demonstrate the potential to include this additional data source to complement fisheries data, especially in data-poor countries. With respect to Brazil specifically, we identified a decrease in both the average trophic level and size of the species consumed. While the consumption of endangered species had always been low, most of these species changed over time, thereby suggesting that many, especially elasmobranchs, may have become rare on the plates. Although it may be hard to fully isolate cultural changes from biodiversity changes when it comes to analyzing consumption data, by examining diets it is possible to identify aspects worth investigating further, such as, whether the decrease in dietary trophic levels mirrors a decrease in environmental trophic levels. In places where fisheries data are either inexistent or limited, diet track surveys, such as household expenditure programs, can help trace the changes caused by fisheries in stocks and habitats.

Age, growth, maturity and extinction risk of an exploited and endangered skate, Atlantoraja castelnaui, from off Uruguay and northern Argentina

The spotback skate Atlantoraja castelnaui (Arhynchobatidae) is a large and threatened skate species subjected to fishing pressure, endemic to the Southwest Atlantic that occurs from Rio de Janeiro, Brazil, to San Jorge Gulf, Argentina. The age, growth, age at maturity and the maximum intrinsic rate of population increase r_max of A. castelnaui were studied using 152 specimens collected from off Uruguay and north Argentina (35°-42° S), between June 2013 and February 2020. Vertebrae from 143 individuals were used for ageing (females: n = 83, size range 404-1300 mm total length, TL; males: n = 60, size range 400-1270 mm TL). Maximum ages determined for females and males were 30 and 28 years, respectively. To fit growth models, non-linear and Bayesian estimation approaches were considered. For the first approach, a set of four candidate growth (size-at-age) models were fitted: three-parameter von Bertalanffy, two-parameter von Bertalanffy with fixed L₀ , Gompertz and Logistic. In the second approach, von Bertalanffy, Gompertz and Logistic were fitted. For non-linear estimation, model selection indicated that the entire set of candidate growth models were supported by the data. The von Bertalanffy was selected as the best model for Bayesian estimation. There were no differences in growth between sexes. For the sexes combined, the von Bertalanffy growth model by Bayesian method was considered the most adequate to describe the growth of A. castelnaui (growth mean parameters ± S.D.: L_∞  = 1210.29 ± 40.68 mm; k = 0.12 ± 0.01 years^-1 ; L₀  = 179.20 ± 11.62 mm). The age at maturity was estimated at 16.21 and 14.04 years for females and males, respectively. The maximum intrinsic rate of population increase r_max was estimated as 0.252 years^-1 . Life-history traits and r_max provided in the present study suggest that this species has a relatively low productivity and may be vulnerable to an intense fishing pressure.

Current and future considerations for shark conservation in the Northeast and Eastern Central Pacific Ocean

Sharks are iconic and ecologically important predators found in every ocean. Because of their ecological role as predators, some considered apex predators, and concern over the stability of their populations due to direct and indirect overfishing, there has been an increasing amount of work focussed on shark conservation, and other elasmobranchs such as skates and rays, around the world. Here we discuss many aspects of current shark science and conservation and the path to the future of shark conservation in the Northeastern and Eastern Central Pacific. We explore their roles in ecosystems as keystone species; the conservation measures and laws in place at the international, national, regional and local level; the conservation status of sharks and rays in the region, fisheries for sharks in the Northcentral Pacific specifically those that target juveniles and the implications to shark conservation; a conservation success story: the recovery of Great White Sharks in the Northeast Pacific; public perceptions of sharks and the roles zoos and aquariums play in shark conservation; and the path to the future of shark conservation that requires bold partnerships, local stakeholders and innovative measures.

Evaluating artisanal fishing of globally threatened sharks and rays in the Bay of Bengal, Bangladesh

Sharks and rays are at risk of extinction globally. This reflects low resilience to increasing fishing pressure, exacerbated by habitat loss, climate change, increasing value in a trade and inadequate information leading to limited conservation actions. Artisanal fisheries in the Bay of Bengal of Bangladesh contribute to the high levels of global fishing pressure on elasmobranchs. However, it is one of the most data-poor regions of the world, and the diversity, occurrence and conservation needs of elasmobranchs in this region have not been adequately assessed. This study evaluated elasmobranch diversity, species composition, catch and trade within the artisanal fisheries to address this critical knowledge gap. Findings show that elasmobranch diversity in Bangladesh has previously been underestimated. In this study, over 160000 individual elasmobranchs were recorded through landing site monitoring, comprising 88 species (30 sharks and 58 rays) within 20 families and 35 genera. Of these, 54 are globally threatened according to the IUCN Red List of Threatened Species, with ten species listed as Critically Endangered and 22 species listed as Endangered. Almost 98% juvenile catch (69-99% for different species) for large species sand a decline in numbers of large individuals were documented, indicating unsustainable fisheries. Several previously common species were rarely landed, indicating potential population declines. The catch pattern showed seasonality and, in some cases, gear specificity. Overall, Bangladesh was found to be a significant contributor to shark and ray catches and trade in the Bay of Bengal region. Effective monitoring was not observed at the landing sites or processing centres, despite 29 species of elasmobranchs being protected by law, many of which were frequently landed. On this basis, a series of recommendations were provided for improving the conservation status of the elasmobranchs in this region. These include the need for improved taxonomic research, enhanced monitoring of elasmobranch stocks, and the highest protection level for threatened taxa. Alongside political will, enhancing national capacity to manage and rebuild elasmobranch stocks, coordinated regional management measures are essential.

Age and growth of the bull shark (Carcharhinus leucas) around Reunion Island, South West Indian Ocean

Sharks exhibit varied demographic strategies depending on both the species and the population location, which make them more or less vulnerable to fishing. Accurate evaluation of local age and growth parameters is therefore fundamental for the sustainable management of their stocks. Although demographic parameters have been assessed for bull shark (Carcharhinus leucas) populations in several locations of the world, this information is missing so far around Reunion Island, in the south-west Indian Ocean. To fill this gap of knowledge, age and growth data were gathered from the vertebrae of 140 individuals of C. leucas (77 females and 63 males, mostly adults) fished around the island between 2012 and 2019. After verification of the annual deposition of growth band pairs on these structures using relative marginal increment analysis on 40 individuals, band pairs were counted along the vertebral centrum for each individual. Thanks to this approach, growth was shown to significantly differ between male and female C. leucas around Reunion Island, with respective von Bertalanffy growth model equations of L_t  =  314 1 - e - 0.0814 t + 5.45 and L_t  = 321.5 1 - e - 0.0999 t + 3.420 . Indeed, the females of the species fished in this area were significantly (P < 0.001) larger than local males, with an estimated difference in size of ~16.1 cm at 20 years old. They also apparently reach older ages, with an estimated maximum age of 33.50 years, against 29.75 years only for the males. The estimated size at birth around the island is larger than elsewhere in the world, varying from 92.30 to 100.00 cm depending on the method used. These results confirm that the population of C. leucas around Reunion Island exhibits a K-selected strategy, which makes it highly vulnerable to fishing pressure.

Testosterone and semen seasonality for the sand tiger shark Carcharias taurus†

Understanding the fundamental reproductive biology of a species is the first step toward identifying parameters that are critical for reproduction and for the development of assisted reproductive techniques. Ejaculates were collected from aquarium (n = 24) and in situ (n = 34) sand tiger sharks Carcharias taurus. Volume, pH, osmolarity, sperm concentration, motility, status, morphology, and plasma membrane integrity were assessed for each ejaculate. Semen with the highest proportion of motile sperm was collected between April and June for both in situ and aquarium sand tiger sharks indicating a seasonal reproductive cycle. Overall, 17 of 30 semen samples collected from aquarium sharks from April through June contained motile sperm compared to 29 of 29 of in situ sharks, demonstrating semen quality differences between aquarium and in situ sharks. Sperm motility, status, morphology, and plasma membrane integrity were significantly higher (P < 0.05) for in situ compared to aquarium sand tiger sharks. Testosterone was measured by an enzyme immunoassay validated for the species. Testosterone concentration was seasonal for both aquarium and in situ sharks with highest concentrations measured in spring and lowest in summer. In situ sharks had higher (P < 0.05) testosterone concentration in spring than aquarium sharks. This study demonstrated annual reproduction with spring seasonality for male sand tiger sharks through marked seasonal differences in testosterone and semen production. Lower testosterone and poorer semen quality was observed in aquarium sharks likely contributing to the species' limited reproductive success in aquariums.

A Perspective on the Role of Eco-Certification in Eliminating Illegal, Unreported and Unregulated Fishing

Illegal, unreported and unregulated (IUU) fishing activities threaten marine biodiversity, livelihoods, food security, and human rights across the globe. Often occurring in waters that are difficult to control, and across multi-sector, transboundary, value chains that are hard to regulate, such a complex and heterogeneous problem requires multiple strategies beyond sovereign nations’ legislation alone. Here we explore the mechanisms through which eco-certification, by fostering private-public and cross-jurisdiction cooperation, can incentivize fishers to adopt best practices in harvesting and ecosystem impacts mitigation, increase the transparency of fishery operations and accountability to suppliers. The Marine Stewardship Council (MSC) sets globally recognized standards for fisheries sustainability and supply chain assurance, based on the FAO Code of Conduct for Responsible Fisheries. Building on the MSC experience of over 400 certified fisheries representing 18% of global wild marine catch, we analyze examples and available information on the changes achieved by the seafood industry through engagement with the program, with particular focus on the elimination or reduction of illegal, unreported or unregulated fishing practices. We propose here that different, interlinked mechanisms come into play: the Standards provide best practice guidelines for improved catch documentation, monitoring, control and surveillance (MCS), and strengthening regulations. These lead to change either through (1) direct improvements required for fisheries to achieve the certificate (e.g., in Fishery Improvement Projects) or, (2) once certified, to maintain the certificate, or (3) as an emergent effect of the engagement process itself, requiring stakeholder cooperation and transparent information-sharing leading to a greater culture of compliance, and (4), as an effect of strengthening chain of custody documentation and standardizing it across jurisdictions. We also discuss limitations, such as the capacity for fisheries in low-income regions to embark on the management and social reform required, and evolving challenges in seafood sustainability, such as ethical concerns for forced and child labor and shark finning. While not the single silver bullet against such a complex problem, we argue that certification is an important tool in addressing IUU fishing.

Complex Human-Shark Conflicts Confound Conservation Action

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.

Quantifying the unreported and unaccounted domestic and foreign commercial catch of sharks and rays in Western Australia

Reliable catch information is scarce for most sharks and rays worldwide, with almost half of the stocks considered to be Data Deficient due to limited species-specific catch statistics. Western Australia (WA) hosts a diverse number of shark and ray species, some of which are considered to be threatened with extinction at a global level. Commercial catch statistics only account for shark and ray landings. The present study used the best available information to reconstruct unaccounted and unreported catches for 47 shark and ray taxa to better understand the impact of fishing. For some species, there was good agreement between reconstructed catches and reported landings, but overall reconstructed catches were 57% higher than those derived from official statistics alone, underestimating the actual extraction level for many species. The reconstructed catch time series provide the basis for the assessment of all species of sharks and rays captured in WA, including protected species that interact with commercial and recreational fisheries.

Illegal, Unreported, and Unregulated Fisheries Threatening Shark Conservation in African Waters Revealed from High Levels of Shark Mislabelling in Ghana

Mislabelling of fish and fish products has attracted much attention over the last decades, following public awareness of the practice of substituting high-value with low-value fish in markets, restaurants, and processed seafood. In some cases, mislabelling includes illegal, unreported, and unregulated (IUU) fishing, contributing to overexploit substitute species that are undetectable when sold under wrong names. This is the first study of DNA barcoding to assess the level of mislabelling in fish marketed in Ghana, focusing on endangered shark species. Genetic identification was obtained from 650 base pair sequences within the cytochrome c oxidase I (COI) gene. All except one of 17 shark fillets analysed were wrongly labelled as compared with none of 28 samples of small commercial pelagic fish and 14 commercial shark samples purchased in Europe. Several substitute shark species in Ghana are endangered (Carcharhinus signatus and Isurusoxyrinchus) and critically endangered (Squatina aculeata). Shark products commercialized in Europe (n = 14) did not reveal mislabelling, thus specific shark mislabelling cannot be generalized. Although based on a limited number of samples and fish markets, the results that reveal trade of endangered sharks in Ghana markets encourage Ghanaian authorities to improve controls to enforce conservation measures.

Using fisher-contributed secondary fins to fill critical shark-fisheries data gaps

Developing-world shark fisheries are typically not assessed or actively managed for sustainability; one fundamental obstacle is the lack of species and size-composition catch data. We tested and implemented a new and potentially widely applicable approach for collecting these data: mandatory submission of low-value secondary fins (anal fins) from landed sharks by fishers and use of the fins to reconstruct catch species and size. Visual and low-cost genetic identification were used to determine species composition, and linear regression was applied to total length and anal fin base length for catch-size reconstruction. We tested the feasibility of this approach in Belize, first in a local proof-of-concept study and then scaling it up to the national level for the 2017-2018 shark-fishing season (1,786 fins analyzed). Sixteen species occurred in this fishery. The most common were the Caribbean reef (Carcharhinus perezi), blacktip (C. limbatus), sharpnose (Atlantic [Rhizoprionodon terraenovae] and Caribbean [R. porosus] considered as a group), and bonnethead (Sphyrna cf. tiburo). Sharpnose and bonnethead sharks were landed primarily above size at maturity, whereas Caribbean reef and blacktip sharks were primarily landed below size at maturity. Our approach proved effective in obtaining critical data for managing the shark fishery, and we suggest the tools developed as part of this program could be exported to other nations in this region and applied almost immediately if there were means to communicate with fishers and incentivize them to provide anal fins. Outside the tropical Western Atlantic, we recommend further investigation of the feasibility of sampling of secondary fins, including considerations of time, effort, and cost of species identification from these fins, what secondary fin type to use, and the means with which to communicate with fishers and incentivize participation. This program could be a model for collecting urgently needed data for developing-world shark fisheries globally. Article impact statement: Shark fins collected from fishers yield data critical to shark fisheries management in developing nations.

Diet, trophic interactions and possible ecological role of commercial sharks and batoids in northern Peruvian waters

The Peruvian sea represents one of the most productive ocean ecosystems and possesses one of the largest elasmobranch fisheries in the Pacific Ocean. Ecosystem-based management of these fisheries will require information on the trophic ecology of elasmobranchs. This study aimed to understand the diet, trophic interactions and the role of nine commercial elasmobranch species in northern Peru through the analysis of stomach contents. A total of 865 non-empty stomachs were analysed. Off northern Peru, elasmobranchs function as upper-trophic-level species consuming 78 prey items, predominantly teleosts and cephalopods. Two distinctive trophic assemblages were identified: (a) sharks (smooth hammerhead shark Sphyrna zygaena, thresher shark Alopias spp. and blue shark Prionace glauca) that feed mainly on cephalopods in the pelagic ecosystem; and (b) sharks and batoids (Chilean eagle ray Myliobatis chilensis, humpback smooth-hound Mustelus whitneyi, spotted houndshark Triakis maculata, Pacific guitarfish Pseudobatos planiceps, copper shark Carcharhinus brachyurus and school shark Galeorhinus galeus) that feed mainly on teleosts and invertebrates in the benthonic and pelagic coastal ecosystem. This study reveals for the first time the diet of T. maculata and the importance of elasmobranchs as predators of abundant and commercial species (i.e., jumbo squid Dosidicus gigas and Peruvian anchovy Engraulis ringens). The results of this study can assist in the design of an ecosystem-based management for the northern Peruvian sea and the conservation of these highly exploited, threatened or poorly understood group of predators in one of the most productive marine ecosystems.

Understanding non-compliance in small-scale fisheries: Shark fishing in Myanmar's Myeik Archipelago

Achieving fisheries compliance is challenging in contexts where enforcement capacity is limited and the incentives for rule-breaking are strong. This challenge is exemplified in Myanmar, where an active shark fishery exists despite a nationwide ban on targeted shark fishing. We used the Kipling method (5W1H) to gather a complete story of non-compliance in five small-scale fishing communities in the Myeik Archipelago. Among 144 fishers surveyed, 49% were aware of the nationwide ban. Shark fishers (24%) tended to be younger individuals who did not own a boat and perceived shark fishing to be prevalent. Compliant fishers were motivated by a fear of sharks and lack of capacity (equipment, knowledge), whereas food and income were cited as key motivations for non-compliance. The results of our study emphasize that in resource-dependent communities, improving compliance for effective shark conservation may require addressing broader issues of poverty, food security and the lack of alternatives.

Half a century of global decline in oceanic sharks and rays

Overfishing is the primary cause of marine defaunation, yet declines in and increasing extinction risks of individual species are difficult to measure, particularly for the largest predators found in the high seas^1-3. Here we calculate two well-established indicators to track progress towards Aichi Biodiversity Targets and Sustainable Development Goals^4,5: the Living Planet Index (a measure of changes in abundance aggregated from 57 abundance time-series datasets for 18 oceanic shark and ray species) and the Red List Index (a measure of change in extinction risk calculated for all 31 oceanic species of sharks and rays). We find that, since 1970, the global abundance of oceanic sharks and rays has declined by 71% owing to an 18-fold increase in relative fishing pressure. This depletion has increased the global extinction risk to the point at which three-quarters of the species comprising this functionally important assemblage are threatened with extinction. Strict prohibitions and precautionary science-based catch limits are urgently needed to avert population collapse^6,7, avoid the disruption of ecological functions and promote species recovery^8,9.

Cross-sectional anatomy, computed tomography, and magnetic resonance imaging of the banded houndshark (Triakis scyllium)

Due to their important phylogenetic position among extant vertebrates, sharks are an invaluable group in evolutionary developmental biology studies. A thorough understanding of shark anatomy is essential to facilitate these studies and documentation of this iconic taxon. With the increasing availability of cross-sectional imaging techniques, the complicated anatomy of both cartilaginous and soft tissues can be analyzed non-invasively, quickly, and accurately. The aim of this study is to provide a detailed anatomical description of the normal banded houndshark (Triakis scyllium) using computed tomography (CT) and magnetic resonance imaging (MRI) along with cryosection images. Three banded houndsharks were scanned using a 64-detector row spiral CT scanner and a 3 T MRI scanner. All images were digitally stored and assessed using open-source Digital Imaging and Communications in Medicine viewer software in the transverse, sagittal, and dorsal dimensions. The banded houndshark cadavers were then cryosectioned at approximately 1-cm intervals. Corresponding transverse cryosection images were chosen to identify the best anatomical correlations for transverse CT and MRI images. The resulting images provided excellent detail of the major anatomical structures of the banded houndshark. The illustrations in the present study could be considered as a useful reference for interpretation of normal and pathological imaging studies of sharks.

Legacy and emerging organic contaminants in two sympatric shark species from Reunion Island (Southwest Indian Ocean): Levels, profiles and maternal transfer

The contamination of tiger sharks (Galeocerdo cuvier) and bull sharks (Carcharhinus leucas) by legacy persistent organic pollutants (POPs) and emerging organic contaminants was investigated in specimens from Reunion Island (Southwest Indian Ocean) in 2018 and 2019. Contamination levels were determined in the muscle of adult individuals of both sexes in relation to biological and trophic parameters. Maternal transfer was additionally investigated in one set of embryos in each species. Polychlorinated biphenyl (PCB), organochlorinated pesticide (OCP) and perfluoroalkylated substance (PFAS) concentrations were 2597 ± 2969, 785 ± 966 and 267 ± 194 pg g-1 ww, respectively, in bull sharks, and 339 ± 270, 1025 ± 946 and 144 ± 53 pg g-1 ww in tiger sharks. The results highlighted higher PCB contamination, and by the heavier congeners, in adult bull sharks versus tiger sharks. The significant differences found in PCB profiles and concentrations suggest that the two species are exposed to different contamination sources. As bull sharks rely on a more coastal habitat for feeding, their higher contamination by PCBs suggests the occurrence of local PCB sources. DDT concentrations were similar in both species, suggesting a more homogeneous contamination on the scale of the Southwest Indian Ocean. Female bull sharks showed lower OCP and PCB concentrations than males, while this trend was not observed in tiger sharks. The ratio of chlorinated contaminants in muscle between the mother and her embryos was related to molecule hydrophobicity in bull shark but not in tiger shark, suggesting that shark mode of gestation, known to be different in the two species, is a key driver of organic contaminant maternal transfer. Finally, the results show that organic contaminant levels in the studied species were lower than those of other shark species in the Southern Hemisphere, related to the limited urbanization and industrialization of Reunion Island.

Genetic diversity in two threatened species of guitarfish (Elasmobranchii: Rhinobatidae) from the Brazilian and Argentinian coasts: an alert for conservation

Abstract The guitarfishes Pseudobatos horkelii and Pseudobatos percellens meet the criteria for threatened status as Critically Endangered (CR) and Endangered (EN), respectively. Both species occur in the Southern Atlantic Ocean. Considering the lack of data on the genetic structure of these species, the present study evaluated the genetic variability and population structure of the P. horkelii and P. percellens in the southern region of Brazil and the northern coast of Argentina, based on sequences of mitochondrial DNA, Control Region (D-loop). Samples of P. horkelii (n = 135) were analyzed in six localities situated in Northern Argentina, along the Brazilian states’ coast. The mean of nucleotide diversity was 0.0053, the ΦST was 0.4277 and demographic analysis of P. horkelii suggests the existence of stability of the populations, with D = 0.9929, FS = 2.0155, SSD = 0.0817, R = 0.2153. In P. percellens (n = 101) were analyzed from six Brazilian localities along the coast of Santa Catarina, Paraná, and São Paulo. The mean nucleotide diversity was 0.0014 and ΦST value of 0.2921, the demographic analysis indicates a high migration rate of P. percellens among the localities evaluated, with D = 0.5222, FS = 0.3528, SSD = 0.01785, R = 0.3890.

Research trends on elasmobranchs from the Brazilian Amazon Coast: a four-decade review

Abstract: Elasmobranchs exhibit the biggest population declines among vertebrates, being considered one of the groups with the highest risk of extinction. The Brazilian Amazon Coast (BAC) is considered a priority area for elasmobranch conservation, as many species are endemic to the region, and most of them are threatened with extinction. The present study made a scientometric analysis using the IRAMUTEQ method (Interface de R pour les Analyses Multidimensionnelles de Textes et de Questionnaires) to evaluate the trends of research with elasmobranchs in BAC in the last four decades. Ten research trends were identified, highlighting “Biodiversity”, “Reproduction”, “Trophic Ecology” and “Conservation”. However, most of the publications found are aimed at understanding the diversity and abundance of species in the region, with the number of studies focused on reproduction, feeding and other aspects of the biology and ecology of elasmobranchs in the BAC being less expressive. Although the research area “Conservation” stood out in the search, the amount of relevant information so that management and conservation measures can be implemented is still low. Lastly, despite following the global trend of studies with elasmobranchs between 2000 and 2010, investigations into the BAC need to advance, especially considering the poor level of basic information on most species (Biology and population dynamics) and the incomplete knowledge of specific composition of elasmobranch species in the entire area, aspects relevant to conservation and more applied studies that rely on more recent methodologies and technologies.

Skin and stinger bacterial communities in two critically endangered rays from the South Atlantic in natural and aquarium settings

Bacterial communities of two critically endangered rays from the South Atlantic, the butterfly ray (Gymnura altavela) and the groovebelly ray (Dasyatis hypostigma), were described using 16S rRNA gene metabarcoding. The study characterized the bacterial communities associated with (i) G. altavela in natural (in situ) and aquarium (ex situ) settings, (ii) skin and stinger of G. altavela, and D. hypostigma in aquaria, and (iii) newborns and adults of D. hypostigma. The results revealed potentially antibiotic‐producing bacterial groups on the skin of rays from the natural environment, and some taxa with the potential to benefit ray health, mainly in rays from the natural environment, as well as possible pathogens to other animals, including fish and humans. Differences were observed between the G. altavela and D. hypostigma bacteria composition, as well as between the skin and stinger bacterial composition. The bacterial community associated with D. hypostigma changed with the age of the ray. The aquarium environment severely impacted the G. altavela bacteria composition, which changed from a complex bacterial community to one dominated almost exclusively by two taxa, Oceanimonas sp. and Sediminibacterium sp. on the skin and stinger, respectively.

The current knowledge gap on metallothionein mediated metal-detoxification in Elasmobranchs

Elasmobranchs are particularly vulnerable to environmental contamination, especially pollutants that may bioaccumulate and biomagnify, throughout the trophic web, such as metals. However, Elasmobranch management and conservation plans are challenging, and this group is often neglected regarding ecotoxicological analyses, particularly concerning metal detoxification mechanisms. This article discusses metallothionein (MT) mediated metal detoxification in Elasmobranchs and reflects on the current knowledge gap in this regard.

Physiological Impairment as a Result of Bile Accumulation in an Apex Predator, the Tiger Shark (Galeocerdo cuvier Péron & Lesueur, 1822)

Simple Summary

Sharks rely on a diet with high lipid content, depending on gallbladder proper functioning for lipid emulsification, absorption, and subsequent hepatic storage. The present study reports a physiological impairment due to bile accumulation in juvenile tiger sharks and the possible causes of such condition.

Abstract

Physiological adaptations have evolved to help sharks face rapid periods of feast. Tiger sharks are generalist apex predators that rely on a high-lipid/protein diet. To achieve a satisfactory nutritional condition, proper lipid absorption and hepatic storage are needed. Bile secretion in sharks is low and sporadic but increases during short periods of fasting. The present study describes a physiological impairment caused by bile accumulation in juvenile tiger sharks, possibly due to prolonged fasting. These evidences suggest that, even though sharks have adaptations that prevent them from dying from starvation, alarming physiological alterations might occur. Future studies are needed to assess how such a condition can affect wild populations, as well as possible sublethal consequences that could impact their long-term survival.

Filling the Gap and Improving Conservation: How IUCN Red Lists and Historical Scientific Data Can Shed More Light on Threatened Sharks in the Italian Seas

Chondrichthyans are one of the most threatened marine taxa worldwide. This is also the case in the Mediterranean Sea, which is considered an extinction hotspot for rays and sharks. The central position of the Italian peninsula makes it an ideal location for studying the status and changes of this sea. There is a lack of biological, ecological and historical data when assessing shark populations, which is also highlighted in the Red List of Threatened Species compiled by the International Union for the Conservation of Nature (IUCN). Historical data can provide important information to better understand how chondrichthyan populations have changed over time. This study aims to provide a clearer understanding of the changes in distribution and abundance of eight shark species in the Italian seas that are currently classified as at risk of extinction by the IUCN. In this respect, a bibliographic review was conducted on items from the 19th century to the first half of the 20th century, focusing on the selected species. The results show that all sharks were considered common until the beginning of the 20th century but have declined since, with a clear negative trend, mainly in the past 70 years. The strong local decline has been attributed to overexploitation, bycatch, habitat loss, depletion of prey items and environmental pollution. Furthermore, historical data also allow us to avoid the issue of a ‘shifting baseline’, in which contemporary abundances are assumed to be “normal”. Using historical data to further our knowledge of the marine environment is becoming increasingly common, and is fundamental in understanding human impact and evaluating mitigation measures to manage and conserve marine species and environments.

Integrative taxonomy identifies a new stingray species of the genus Hypanus Rafinesque, 1818 (Dasyatidae, Myliobatiformes), from the Tropical Southwestern Atlantic

An integrative approach by the congruence of genetics, morphology and ecological niche modelling (ENM) was used to delimit a new species of Hypanus (Rafinesque, 1818), a recently resurrected genus of marine stingrays comprising eight species, five of which occur in the western Atlantic. The species with the widest distribution, Hypanus americanus (Hildebrand and Schroeder, 1928), from the northeastern coast of the United States to southeastern Brazil, was demonstrated to be paraphyletic based on protein-coding mitochondrial genome analyses. This data set also indicates that the genetic distance between the new species Hypanus berthalutzae sp. nov. and its three closely related species (H. americanus, H. longus and H. rudis) varies from 0.82% to 3.14%. In addition, Bayesian Analysis of Population Similarity using the mitochondrial gene mt-nd2 supports the separation of H. berthalutzae sp. nov. (southwestern Atlantic) from its sister species H. rudis (eastern Atlantic). Similarly, morphological and morphometric analyses corroborated four morphotypes within the H. americanus species group and indicated the ventral caudal fold height and length and interspiracular and interorbital lengths as useful measurements to distinguish among them. Claspers of adult males also exhibit morphological differences among species. The ENM agreed with molecular and morphological analyses and delimits the distribution of H. berthalutzae sp. nov. to shallow areas close to shore along the Brazilian coast, from the mouth of the Amazon River to São Paulo State, including the northeastern oceanic islands, suggesting that the great outflow of fresh water and sediments and the Mid-Atlantic Ridge might act as barriers. The integration of these data to describe a new species provides information relevant to their conservation status, because all species of the H. americanus species group are under the "data-deficient" status.

Artificial habitats host elevated densities of large reef-associated predators

Large predators play important ecological roles, yet many are disproportionately imperiled. In marine systems, artificial reefs are often deployed to restore degraded reefs or supplement existing reefs, but it remains unknown whether these interventions benefit large predators. Comparative field surveys of thirty artificial and natural reefs across ~200 km of the North Carolina, USA coast revealed large reef-associated predators were more dense on artificial than natural reefs. This pattern was associated with higher densities of transient predators (e.g. jacks, mackerel, barracuda, sharks) on artificial reefs, but not of resident predators (e.g., grouper, snapper). Further analyses revealed that this pattern of higher transient predator densities on artificial reefs related to reef morphology, as artificial reefs composed of ships hosted higher transient predator densities than concrete reefs. The strength of the positive association between artificial reefs and transient predators increased with a fundamental habitat trait–vertical extent. Taller artificial reefs had higher densities of transient predators, even when accounting for habitat area. A global literature review of high trophic level fishes on artificial and natural habitats suggests that the overall pattern of more predators on artificial habitats is generalizable. Together, these findings provide evidence that artificial habitats, especially those like sunken ships that provide high vertical structure, may support large predators.

Commercial fish ELISA kits have a limited capacity to detect different fish species and their products

BACKGROUND

Fish is a major food and allergen source, requiring safety declarations on packages. Enzyme-linked immunosorbent assays (ELISAs) are often used to ensure that the product meets the required standards with regard to the presence of allergens. Over 1000 different fish species are traded and consumed worldwide, and they are increasingly provided by aquaculture. Up to 3% of the general population is at risk of sometimes fatal allergic reactions to fish, requiring strict avoidance of this commodity. The aim of this study is to evaluate the capacity of three commercially available ELISA tests to detect a wide variety of bony and cartilaginous fish and their products, which is essential to ensure reliable and safe food labeling.

RESULTS

The detection rates for 57 bony fish ranged from 26% to 61%. Common European and North American species, including carp, cod, and salmon species, demonstrated a higher detection rate than those from the Asia-Pacific region, including pangasius and several mackerel and tuna species. Among the 17 canned bony fish products, only 65% to 86% were detected, with tuna showing the lowest rate. None of the cartilaginous fish (n = 9), other vertebrates (n = 8), or shellfish (n = 5) were detected.

CONCLUSIONS

We demonstrated that three commercial fish ELISA kits had a limited capacity to detect fish and their products. The complexity of fish as a protein source that is increasingly utilized means that there is an urgent need for improved detection methods. This is crucial for the food industry to provide safe seafood products and comply with international legislation. © 2020 Society of Chemical Industry.

Global change in the functional diversity of marine fisheries exploitation over the past 65 years

Overexploitation is recognized as one of the main threats to global biodiversity. Here, we report a widespread change in the functional diversity of fisheries catches from the large marine ecosystems (LMEs) of the world over the past 65 years (1950 to 2014). The spatial and temporal trends of functional diversity exploited from the LMEs were calculated using global reconstructed marine fisheries catch data provided by the Sea Around Us initiative (including subsistence, artisanal, recreational, industrial fisheries, and discards) and functional trait data available in FishBase. Our analyses uncovered a substantial increase in the functional richness of both ray-finned fishes (80% of LMEs) and cartilaginous species (sharks and rays) (75% of LMESs), in line with an increase in the taxonomic richness, extracted from these ecosystems. The functional evenness and functional divergence of these catches have also altered substantially over the time span of this study, with considerable geographic variation in the patterns detected. These trends show that global fisheries are increasingly targeting species that play diverse roles within the marine ecosystem and underline the importance of incorporating functional diversity in ecosystem management.

Macro-litter ingestion in deep-water habitats: is an underestimation occurring?

Marine litter affects marine organisms, posing threats to biodiversity conservation and to ecosystem structure and functioning. Providing a suitable assessment of marine litter effects on marine life through bioindicator species is crucial to drive an effective waste management policy. However, to date no standardized tool has been developed to describe and monitor the impact of marine macro-litter on marine life within deep-water habitats. Modifying the protocol proposed to monitor macro-litter ingestion by the loggerhead sea turtle Caretta caretta, we perform a preliminary investigation on the suitability of different elasmobranch species for monitoring macro-litter ingestion in deep-sea. A total of 122 specimens representing 7 elasmobranch species were collected and examined. External visual inspections documented no clear evidences of disease due to marine litter entanglement. A total of 7 ingested litter items were found in the stomach or in the esophagus of 6 specimens of 4 different species (frequency of occurrence = 4.9%), with a maximum number of 2 items per specimen. No litter items were found in the intestinal contents, as well as no evidence of gastrointestinal blockages due to litter items were detected. The low number of collected litter items suggests that the number of samples required is too large for a feasible monitoring program. Moreover, we observed that the anatomy of the intestinal spiral valve may represent an obstacle to the transit of macro-litter items, which could be spontaneously regurgitated as it happens in the selective elimination of undigested remains, such as bones and scales. Therefore, macro-litter retention time in the gastrointestinal tract of elasmobranchs could be brief and shorter than retention time of food. This may lead to an underestimation of macro-litter ingestion frequency by deep-water elasmobranchs. This study reports the first evidence of plastic ingestion by the kitefin shark Dalatias licha.