The importance of considering genetic diversity in shark and ray conservation policies

Many populations of elasmobranchs (sharks and rays) are experiencing severe declines due to the high demand for shark fins in Asia, the activities of unregulated fisheries, and increases in shark and ray catches. Recently, the effects of the decline in the populations of marine fish species on genetic diversity have drawn increasing attention; however, only a few studies have addressed the genetic diversity of shark and ray populations. Here, we report the results of a quantitative analysis of the genetic diversity of shark and ray species over the past 20 years and discuss the importance and utility of this genetic information for fisheries management and conservation policies. Furthermore, we suggest future actions important for minimizing the gaps in our current knowledge of the genetic diversity of shark and ray species and to minimize the information gap between genetic scientists and policymakers. We suggest that shark and ray fisheries management and conservation policies consider genetic diversity information, such as the management unit, effective population size (Ne), haplotype and nucleotide diversity, observed heterozygosity, and allelic richness, because the long-term survival of a species is strongly dependent on the levels of genetic diversity within and between populations. In addition, sharks and rays are a group of particular interest for genetic conservation due to their remarkable life histories.     

Freshwater elasmobranchs: a review of their physiology and biochemistry

Only 5% of elasmobranch species live in freshwater (FW) compared to more than 40% of known teleost species. The factors affecting the poor penetration of elasmobranchs into FW environments are currently unknown, however, an important consideration may be the high urea requirement of many proteins in marine elasmobranchs. Urea is an important osmolyte in marine elasmobranchs and must be reduced in dilute environments. There are three identifiable stages in the successful colonization of FW. The euryhaline marine species freely entering and leaving FW represent the initial stage of FW colonization. In this group, there is an apparent inability to eliminate all urea due to protein integrity issues and this results in energy and nitrogen losses that may constrain growth and reproduction. The second stage is represented by those species that live entirely in FW but must also retain some urea. This group also suffers from the same constraints as the first group. These two groups have kidneys and sensory organs that more closely resemble strictly marine forms. The third and final stage is represented by the Potamotrygonid stingrays where the need for urea in FW has been eliminated. Consequently nitrogen and energy losses are reduced and those sections of the kidney needed for urea conservation have been eliminated. The driving force for such modifications is a reduction in urea levels and the concomitant saving of energy needed for urea synthesis. Other physiological adaptations associated with survival in FW include giving birth to live young, the capacity of sperm to be activated in freshwater and modifications of the electrosensory system to function in a low conductivity environment. The need for many anatomical, metabolic and physiological modifications for FW existence may constrain the rapidity and hence the frequency of FW colonization, compared to the situation in the more advanced osmoregulating teleosts. Once optimally adapted to FW, recolonization of sea water by elasmobranchs is problematic due to the loss of urea synthetic capacity and renal structures for urea retention.     

Recovery potential and conservation options for elasmobranchs

Many elasmobranchs have experienced strong population declines, which have been largely attributed to the direct and indirect effects of exploitation. Recently, however, live elasmobranchs are being increasingly valued for their role in marine ecosystems, dive tourism and intrinsic worth. Thus, management plans have been implemented to slow and ultimately reverse negative trends, including shark-specific (e.g. anti-finning laws) to ecosystem-based (e.g. no-take marine reserves) strategies. Yet it is unclear how successful these measures are, or will be, given the degree of depletion and slow recovery potential of most elasmobranchs. Here, current understanding of elasmobranch population recoveries is reviewed. The potential and realized extent of population increases, including rates of increase, timelines and drivers are evaluated. Across 40 increasing populations, only 25% were attributed to decreased anthropogenic mortality, while the majority was attributed to predation release. It is also shown that even low exploitation rates (2-6% per year) can halt or reverse positive population trends in six populations currently managed under recovery plans. Management measures that help restore elasmobranch populations include enforcement or near-zero fishing mortality, protection of critical habitats, monitoring and education. These measures are highlighted in a case study from the south-eastern U.S.A., where some evidence of recovery is seen in Pristis pectinata, Galeocerdo cuvier and Sphyrna lewini populations. It is concluded that recovery of elasmobranchs is certainly possible but requires time and a combination of strong and dedicated management actions to be successful.     

The elasmobranchs of Malpelo Flora and Fauna Sanctuary,Colombia

Management and conservation actions in marine-protected areas require baselines for monitoring threatened marine fauna such as elasmobranchs. This article provides evidence of the occurrence of 34 species of elasmobranchs (21 sharks and 13 batoids) in the Malpelo Flora and Fauna Sanctuary, Colombia, including five new records of sharks and three of rays. From 1987 to 2021, new records were obtained by underwater visual census using SCUBA, manned submersibles and deep-ocean cameras to depths of up to 2211 m. Of the recorded species, 21 are considered as threatened taxa (64%) by the IUCN, making the Malpelo Flora and Fauna Sanctuary an essential conservation area for this highly threatened group of species.     

Preface: feeding ecology of elasmobranchs

Elasmobranchs are apical predators in most marine communities where they occur, often playing a substantial role in the food web dynamics of those communities. However, despite their high trophic status they are often poorly studied compared to most commercially important teleosts. Furthermore, despite efforts towards ecosystem-based management, elasmobranchs are still often lumped into generic categories referred to as ??shark?? or ??skate?? unclassified, with limited effort to identify individual species. The role of elasmobranchs in ecosystems has never been more important to our understanding of marine ecology due to high levels of exploitation of many species. Similar to other high trophic level predators, many elasmobranchs have life-history characteristics that make them vulnerable to over-exploitation. Elasmobranch populations are now heavily targeted in many fisheries throughout the world. Increasing exploitation of this group is especially alarming because their feeding ecology is poorly studied and by extension their influence in shaping ecosystems. Given recent increased attention on elasmobranchs in the scientific literature, management and conservation circles, and the general news media, researchers over the past decade have begun to more closely examine the ecological role of this important taxon of fishes. Due to this increasing awareness, and the development of new and innovative methods and analytical techniques, it prompted us to organize an international symposium on the ??Feeding Ecology of Elasmobranchs??. The symposium was held on 10 July 2010, in conjunction with the 27^th annual meeting of the American Elasmobranch Society meetings in Providence, Rhode Island.     

The first reproductive parameters and evidence of multiple paternity in one new spiny dogfish species,Squalus albicaudus (Squaliformes,Squalidae)

Understanding elasmobranch reproductive biology is necessary for species conservation. Multiple paternity (MP) has been reported for elasmobranchs, and this study investigates the reproductive aspects and mating system (paternity genetic analyses) for Squalus albicaudus. Thirteen pregnant females were analysed concerning reproductive parameters, and the mating system was assessed for nine females and their litters. The study found a mean fecundity of 2.84 pups per litter without correlation between total female length and the number of embryos per litter. One litter showed evidence of MP, indicating the presence of polyandrous behaviour of the species.     

Direct and indirect fishery effects on small coastal elasmobranchs in the northern Gulf of Mexico

Globally, bycatch in tropical/subtropical shrimp trawl and longline fisheries is threatening many marine species. Here we examine the joint effects of increased mortality caused by shrimp trawling bycatch, and reduced predation caused by losses of large sharks because of longline fishing. Research surveys in the Gulf of Mexico (1972–2002) demonstrated precipitous declines in shallow water coastal elasmobranchs where shrimping effort was highest (bonnethead 96%, Bancroft's numbfish (lesser electric ray) 98%, smooth butterfly ray > 99%) and consistent increases in deeper water elasmobranchs (Atlantic angel shark, smooth dogfish). These increases are the first empirical support for predation release caused by the loss of large sharks, which have been theorized to structure tropical/subtropical marine ecosystems. Bycatch of elasmobranchs in shrimp trawls is a critical conservation concern which is not solved by present mitigation measures; similar loss of elasmobranchs is expected to be occurring in tropical/subtropical regions worldwide where ever intensive shrimp trawling occurs.     

The physiological response to anthropogenic stressors in marine elasmobranch fishes: a review with a focus on the secondary response

Elasmobranchs (sharks, rays, and skates) are currently facing substantial anthropogenic threats, which expose them to acute and chronic stressors that may exceed in severity and/or duration those typically imposed by natural events. To date, the number of directed studies on the response of elasmobranch fishes to acute and chronic stress are greatly exceeded by those related to teleosts. Of the limited number of studies conducted to date, most have centered on sharks; batoids are poorly represented. Like teleosts, sharks exhibit primary and secondary responses to stress that are manifested in their blood biochemistry. The former is characterized by immediate and profound increases in circulating catecholamines and corticosteroids, which are thought to mobilize energy reserves and maintain oxygen supply and osmotic balance. Mediated by these primary responses, the secondary effects of stress in elasmobranchs include hyperglycemia, acidemia resulting from metabolic and respiratory acidoses, and profound disturbances to ionic, osmotic, and fluid volume homeostasis. The nature and magnitude of these secondary effects are species-specific and may be tightly linked to metabolic scope and thermal physiology as well as the type and duration of the stressor. In fishes, acute and chronic stressors can incite a tertiary response, which involves physiological changes at the organismal level, thereby impacting growth rates, reproductive outputs or investments, and disease resistance. Virtually no studies to date have been conducted on the tertiary stress response in elasmobranchs. Given the diversity of elasmobranchs, additional studies that characterize the nature, magnitude, and consequences of physiological stress over a broad spectrum of stressors are essential for the development of conservation measures. Additional studies on the primary, secondary, and tertiary stress response in elasmobranchs are warranted, with particular emphasis on expanding the range of species and stressors examined. Future studies should move beyond simply studying the effects of known stressors and focus on the underlying physiological mechanisms. Such studies should include the coupling of stress indicators with quantifiable aspects of the stressor, which will allow researchers to test hypotheses on survivorship and, ultimately, derive models that effectively link physiology to mortality. Studies of this nature are essential for decision-making that will result in the effective management and conservation of these species.     

Effects of biological traits on capture-induced parturition in a freshwater stingray and perspectives for species management

Elasmobranchs are particularly vulnerable to overexploitation and population depletion, especially due to their life-history traits, such as low reproductive output and slow growth. Given that capture-induced parturition (abortion or premature birth) is a common consequence of fisheries in elasmobranchs, but still little studied, we investigated how the abortion/premature birth process varies in response to reproductive traits in a freshwater stingray, Potamotrygon amandae. Our results revealed that capture-induced parturition was affected by reproductive traits, such as litter size (one to seven) and gestation stage. The event occurred faster in pregnant females with high litter size during late pregnancy. Also, as found in other elasmobranchs, litter size was positively correlated with maternal size. These findings indicate that larger pregnant females in late pregnancy are more vulnerable to capture-induced parturition. This study improves our understanding of the capture-induced parturition process in stingrays, and provides useful information for management strategies and future recommendations for elasmobranch conservation.     

Sustainability of threatened species displayed in public aquaria,with a case study of Australian sharks and rays

Zoos and public aquaria exhibit numerous threatened species globally, and in the modern context of these institutions as conservation hubs, it is crucial that displays are ecologically sustainable. Elasmobranchs (sharks and rays) are of particular conservation concern and a higher proportion of threatened species are exhibited than any other assessed vertebrate group. Many of these lack sustainable captive populations, so comprehensive assessments of sustainability may be needed to support the management of future harvests and safeguard wild populations. We propose an approach to identify species that require an assessment of sustainability. Species at risk of extinction in the wild were considered to be those assessed as threatened (CR, EN or VU) on the IUCN Red List of Threatened Species, or data deficient species that may be at an elevated risk of extinction due to life history traits and habitat associations. We defined sustainable captive populations as self-maintaining, or from a source population that can sustain harvest levels without risk of population declines below sustainable levels. The captive breeding and wild harvest records of at risk species displayed by Australian aquaria were examined as a case study. Two species, largetooth sawfish Pristis pristis and grey nurse shark Carcharias taurus, were found to have unsustainable captive populations and were identified as high priorities for comprehensive sustainability assessments. This review highlights the need for changes in permitting practices and zoo and aquarium record management systems to improve conservation outcomes for captive elasmobranchs.     

Forecasting elasmobranch survival following exposure to severe stressors

Current fishing practices and habitat degradation in most of the world's oceans pose significant threats to marine fish including elasmobranchs. The accurate prediction of survival probability for elasmobranchs subjected to prolonged immobilisation and diminished oxygen availability during capture and a vulnerable state post-release, is reliant on selecting a reliable set of biomarkers to profile as well as using them to design pre-release interventions which minimise elasmobranch death. The purpose of this review is: i) to make a case for the need to develop new biomarkers to use in conjunction with blood chemistry; ii) to briefly present the survival strategies used by other vertebrates subjected to diminished oxygen iii) to discuss new approaches to forecasting the effect that altered physiological and biochemical markers have on long-term survival with a particular emphasis on oxidative stress, the adenylate energy charge, heat shock protein expression and the capacity for repair, so that a more detailed profile of the qualities of elasmobranch survivorship can be constructed. In addition, the review will discuss the relevance of biomarkers to field samples as well as their incorporation into laboratory based research, aimed at providing physiological and biochemical data to inform conservation management.     

A review of the application of molecular genetics for fisheries management and conservation of sharks and rays

Since the first investigation 25 years ago, the application of genetic tools to address ecological and evolutionary questions in elasmobranch studies has greatly expanded. Major developments in genetic theory as well as in the availability, cost effectiveness and resolution of genetic markers were instrumental for particularly rapid progress over the last 10 years. Genetic studies of elasmobranchs are of direct importance and have application to fisheries management and conservation issues such as the definition of management units and identification of species from fins. In the future, increased application of the most recent and emerging technologies will enable accelerated genetic data production and the development of new markers at reduced costs, paving the way for a paradigm shift from gene to genome-scale research, and more focus on adaptive rather than just neutral variation. Current literature is reviewed in six fields of elasmobranch molecular genetics relevant to fisheries and conservation management (species identification, phylogeography, philopatry, genetic effective population size, molecular evolutionary rate and emerging methods). Where possible, examples from the Indo-Pacific region, which has been underrepresented in previous reviews, are emphasized within a global perspective.     

Elasmobranchs in southern Indonesian fisheries: the fisheries, the status of the stocks and management options

The biology of elasmobranchs makes them very vulnerable to fishing pressure and there is increasing international concern over their exploitation. In northern Australia the stocks of some species may be shared with those in southern Indonesia. Indonesia has the highest landings of elasmobranchs worldwide (>100,000 t p.a.) and millions of Indonesian artisanal fishers rely heavily on elasmobranchs taken in target fisheries. They are also taken by industrial trawlers and as bycatch in pelagic tuna fisheries. This paper, resulting from a collaborative project between Australia and Indonesia, summarises the elasmobranch fisheries; the characteristics of the fisheries are outlined, the status of the stocks are assessed, and management options described and discussed. The project focussed on representative markets and fish landing sites in southern Indonesia from 2001 to 2005. Data were from market surveys, the records of the Indonesian Directorate General of Capture Fisheries, and from research cruises. Data from the ongoing tuna monitoring programme showed that shark bycatch from the tuna fleets forms about 11% of shark landings in Indonesia. Yield per recruit and related analyses were used to integrate biological information to indicate the productivity of each species to allow for management policy options and constraints. Research cruise data show that catch rates of elasmobranchs in the Java Sea declined by at least one order of magnitude between 1976 and 1997. The results indicate strongly that many of the shark and ray species in Indonesia are overfished and that the most effective management strategy may need to involve capacity control, such as licencing, gear restrictions and catch limits, together with controls on the fin trade.     

Building strong relationships between conservation genetics and primary industry leads to mutually beneficial genomic advances

Several reviews in the past decade have heralded the benefits of embracing high‐throughput sequencing technologies to inform conservation policy and the management of threatened species, but few have offered practical advice on how to expedite the transition from conservation genetics to conservation genomics. Here, we argue that an effective and efficient way to navigate this transition is to capitalize on emerging synergies between conservation genetics and primary industry (e.g., agriculture, fisheries, forestry and horticulture). Here, we demonstrate how building strong relationships between conservation geneticists and primary industry scientists is leading to mutually‐beneficial outcomes for both disciplines. Based on our collective experience as collaborative New Zealand‐based scientists, we also provide insight for forging these cross‐sector relationships.     

我国生物多样性保护标准体系现状、问题与建议

目前我国生物多样性保护标准体系还不完善, 尚不能满足生物多样性保护工作的现实需求。为了提升我国生物多样性保护标准化水平, 本文根据《生物多样性公约》确立的“保护生物多样性、可持续利用其组成部分以及公平合理分享由利用遗传资源而产生的惠益” 3大目标, 围绕生态系统、物种、基因3个层次, 以现行有效的国家标准和行业标准为研究基础, 采用相关关键词检索现有生物多样性保护标准形成标准清单(共包含1,032项标准), 并以此标准清单为研究对象, 深入分析我国生物多样性保护标准体系。本研究发现我国生物多样性保护标准体系的现状主要是分行业管理、基本覆盖各主要任务、涵盖多类别, 但仍存在标准间缺乏系统性和完整性、标准规范质量不高且使用率低, 与国际标准衔接不够的问题。以现行生物多样性保护标准体系存在的问题为切入点, 围绕生物多样性保护的主要任务和职责定位, 提出了我国生物多样性标准体系三维结构框架(包含行业、任务和类别3个维度)的构建设想。最后, 本文从筹建全国生物多样性保护标准化技术委员会、及时开展标准制修订工作、加强科学技术支撑、推动我国标准与国际标准接轨4个面提出了相关建议, 以期为建设更加先进适用的生物多样性保护标准体系提供参考。     

Retrograde labeling and fine structure of olfactory receptor neurons in cat sharks

Ciliated and microvillar olfactory receptor cells have been reported in many fish species, including teleosts and elasmobranchs. Morphological studies have suggested that microvillar cells are the only olfactory receptor cells in the elasmobranchs; however, there is no direct evidence for this hypothesis. Here we used a cat shark (Scyliorhinus torazame) to determine the cell type of the olfactory receptor cells in elasmobranchs. Retrograde labeling with a fluorescent dye, Dil, labeled only cells in the second layer from the surface of the olfactory epithelium, suggesting that ciliated cells located in the surface layer are not olfactory receptor cells. In addition, electron microscopic observation revealed that the labeled cells in the second layer have a thin dendritic knob extending from the cell body to the free surface of the epithelium. A part of the dendritic knob facing the mucous layer did not have ciliary structures. These results provide evidence that the aciliate cells are the only olfactory receptor cells in the cat shark olfactory organ.     

Vision in elasmobranchs and their relatives: 21st century advances

This review identifies a number of exciting new developments in the understanding of vision in cartilaginous fishes that have been made since the turn of the century. These include the results of studies on various aspects of the visual system including eye size, visual fields, eye design and the optical system, retinal topography and spatial resolving power, visual pigments, spectral sensitivity and the potential for colour vision. A number of these studies have covered a broad range of species, thereby providing valuable information on how the visual systems of these fishes are adapted to different environmental conditions. For example, oceanic and deep-sea sharks have the largest eyes amongst elasmobranchs and presumably rely more heavily on vision than coastal and benthic species, while interspecific variation in the ratio of rod and cone photoreceptors, the topographic distribution of the photoreceptors and retinal ganglion cells in the retina and the spatial resolving power of the eye all appear to be closely related to differences in habitat and lifestyle. Multiple, spectrally distinct cone photoreceptor visual pigments have been found in some batoid species, raising the possibility that at least some elasmobranchs are capable of seeing colour, and there is some evidence that multiple cone visual pigments may also be present in holocephalans. In contrast, sharks appear to have only one cone visual pigment. There is evidence that ontogenetic changes in the visual system, such as changes in the spectral transmission properties of the lens, lens shape, focal ratio, visual pigments and spatial resolving power, allow elasmobranchs to adapt to environmental changes imposed by habitat shifts and niche expansion. There are, however, many aspects of vision in these fishes that are not well understood, particularly in the holocephalans. Therefore, this review also serves to highlight and stimulate new research in areas that still require significant attention.     

Phylogenetic and ecological factors influencing the number and distribution of electroreceptors in elasmobranchs

Electroreception is found throughout the animal kingdom from invertebrates to mammals and has been shown to play an important role in prey detection, facilitating social behaviours, the detection of predators and orientation to the earth's magnetic field for navigation. Electroreceptors in elasmobranchs, the ampullae of Lorenzini, detect minute electric fields and independently process these stimuli, thereby providing spatial information to the central nervous system on the location of a source, often potential prey. The ampullae of Lorenzini are individually connected to a single somatic pore on the surface of the skin, with the spatial separation of each pore directly influencing how electrical stimuli are detected and processed. Pore abundance varies across taxonomic groups resulting in unique species-specific differences. The intricate distribution patterns created by the specific positioning of somatic pores on the head are, however, consistent within families, resulting in patterns that are identifiable at higher taxonomic levels. As elasmobranchs evolved, the electrosensory system became more complex and highly specialized, which is evident by a general trend of increasing pore abundance over time. The elasmobranch electrosensory system has evolved to operate efficiently under the environmental conditions of the particular habitat in which a species lives. For example, reduced pore abundance is evident in oceanic pelagic elasmobranchs, for whom visual cues are thought to be of great importance. Pore abundance and spatial distribution may be influenced by multiple factors including head morphology, phylogeny, feeding behaviour and habitat.     

Molecular phylogeny of elasmobranchs inferred from mitochondrial and nuclear markers

The elasmobranchs (sharks, rays and skates) being the extant survivors of one of the earliest offshoots of the vertebrate evolutionary tree are good model organisms to study the primitive vertebrate conditions. They play a significant role in maintaining the ecological balance and have high economic value. Due to over-exploitation and illegal fishing worldwide, the elasmobranch stocks are being decimated at an alarming rate. Appropriate management measures are necessary for restoring depleted elasmobranch stocks. One approach for restoring stocks is implementation of conservation measures and these measures can be formulated effectively by knowing the evolutionary relationship among the elasmobranchs. In this study, a total of 30 species were chosen for molecular phylogeny studies using mitochondrial cytochrome c oxidase subunit I, 12S ribosomal RNA gene and nuclear Internal Transcribed Spacer 2. Among different genes, the combined dataset of COI and 12S rRNA resulted in a well resolved tree topology with significant bootstrap/posterior probabilities values. The results supported the reciprocal monophyly of sharks and batoids. Within Galeomorphii, Heterodontiformes (bullhead sharks) formed as a sister group to Lamniformes (mackerel sharks): Orectolobiformes (carpet sharks) and to Carcharhiniformes (ground sharks). Within batoids, the Myliobatiformes formed a monophyly group while Pristiformes (sawfishes) and Rhinobatiformes (guitar fishes) formed a sister group to all other batoids.