For data-limited fish species, sustainable management frequently relies on biological metrics that are derived from life-history trait data, as opposed to high-resolution time series of catch and abundance. These biological metrics are used to assess a species' recovery potential at low population densities, as well as their extinction risk. However, for really data poor species, the life-history traits required to derive these metrics are also often only partially known. Addressing this gap is essential for informing regulatory and conservation actions for vulnerable species and stocks lacking assessments. We developed a generalisable, phylogenetically informed framework for imputing missing life-history traits across different taxa and applied it to 57 species within the order Rhinopristiformes (rhino rays), an evolutionarily distinct and highly threatened group with notably sparse life-history data. We then used the imputed traits to derive four key management and conservation metrics: steepness of the Beverton-Holt stock-recruitment relationship, spawning potential ratio at maximum sustainable yield, maximum intrinsic population growth rate and generation length. We found strong correlations between mean life-history traits and three management metrics. While uncertainty in management metrics remained high due to intraspecific variability, measurement error and limited data, using reconstructed traits reduced uncertainty compared to using surrogate trait data from other populations or congeneric species. We provide imputed trait values and corresponding management and conservation metrics alongside uncertainty bounds that should be recognised in any subsequent conservation assessments and management strategy evaluations. The proposed framework enables the generation of first-order, evidence-based management and conservation metrics for data-limited taxa, thereby supporting more informed decision-making for species without comprehensive species-level assessments.

International wildlife trade is a major source of biodiversity loss, yet many species lie hidden within aggregated data that conceals trade impacts. We overcome this problem for the largest vertebrate wildlife trade globally – shark and ray meat – comprising 438 538 mt yr-1 across more than 150 species, 76% of which are Threatened. Revealed trade contains greater quantities of skates (+10%), hammerheads (+8%), and smoothhounds, dogfishes & tope (+5%), and fewer pelagic sharks (-38%) than previously known. Shorttail yellownose skate, smoothound, silky, mako, and blue sharks are the most underreported meat species, due to aggregated landings from China, Argentina, Japan, and Indonesia, demonstrating international trade in shark and ray meat as a diverse, pervasive, and previously hidden source of fishing mortality for many threatened species. ### Competing Interest Statement The authors have declared no competing interest. Shark Conservation Fund

Deep-sea mining is expected to cause disturbances of sufficient scale and intensity to pose a risk to biodiversity and ecosystem function.1,2,3 We assess the potential impact of deep-sea mining on sharks, rays, and chimaeras in Areas Beyond National Jurisdiction (ABNJ) and identify 30 species (of the total 1,223 marine chondrichthyan species) that overlap spatially with the anticipated mining footprint, specifically through 2 pathways: benthic impacts from physical disturbance and the collector vehicle plume2 and midwater impacts from the discharge plume.4 Most species' depth ranges (83%, 25/30, range: 3%-80%) overlapped vertically with the benthic mining footprint, while all species overlapped with discharge plume scenarios. Further, 17 of these species had >50% depth overlap with benthic impacts of at least one of the mineral types. Seven species were egg-laying, benthic, or benthopelagic, which increases their susceptibility to seabed impacts. Filter-feeding species also had high depth overlap with potential midwater discharge plumes. Nearly two-thirds (60%, 18/30) are already threatened with an elevated risk of extinction, and 64.3% are predicted to be threatened. Our analysis raises concerns that deep-sea mining would compound and worsen their extinction risk. We recommend updated risk assessments of significant adverse impacts to chondrichthyans; robust baseline monitoring prior to, during, and after mining; spatial protections near crust and sulfide mining; and that the discharge plume be set at a minimum depth below 2,000 m or at the seabed to minimize overlap with midwater species.

The global shark meat trade entails diverse and tangled challenges, spanning from issues surrounding traceability and sustainability to its international dimension, involving numerous nations. This study analyzes two decades of shark product trade data using network analysis to assess the role of key trading nations. Results reveal key players in the international shark meat trade network including European Union (EU) (e.g. Spain, Portugal, Italy) and South American (e.g. Uruguay, Brazil) nations, which serve as both intercontinental transfer and redistribution points. On the other hand, the trade of shark fins is highly centralized around Asian markets (notably Hong Kong and Singapore). This underlines the important role and responsibility these trade partners have in the broader trade network to ensure the sustainability, legality and traceability of global shark products. While improved management practices are important, this research advocates for policy solutions such as implementing CITES listings for shark species, improving traceability mechanisms, and enforcing science-based catch limits. Achieving a sustainable shark trade necessitates collaborative global action underpinned by robust EU leadership in regulatory frameworks and ethical practices.

Sharks, rays, and chimaeras are among the most threatened vertebrate lineages. Despite considerable conservation efforts, the extinction risk of sharks continues to rise. We present a quantitative analysis of the shark conservation literature, exploring trends and interconnectivities in key topics using a machine learning approach. We show that shark conservation research is a well interconnected, coherently structured, and rapidly expanding field centred around a conservation nexus linking human-wildlife interactions to species use and management. Shark conservation research is increasingly interdisciplinary and is well prioritised toward key threats that drive the decline of shark populations, both of which are key to effective management. However, we also identify opportunities to further strengthen research and management. These include improved integration of key research topics, enhancing the understanding of combined threats, and greater consideration for the role of sub-lethal impacts. Lastly, we stress that meaningful integration of research topics, rather than simple contextualisation, is essential to building the comprehensive and nuanced understanding necessary to inform effective conservation actions. By leveraging the strengths of the field and addressing its remaining weaknesses, there is hope for a future where sharks thrive and contribute to healthy, resilient marine ecosystems.

As animal populations continue to decline, understanding global patterns of life histories will improve our predictions of species vulnerability and extinction risk to prioritise management. Sharks and rays are threatened with extinction due to overfishing, particularly in the tropics and sub-tropics. Metabolic theory suggests that warm-water species and populations will have a higher maximum intrinsic rate of population increase ( r max) and therefore will be less intrinsically sensitive to exploitation. However, recent empirical work has highlighted a paradox and shown that warm, shallow-water tropical rays have lower r max than cold, deep-water temperate skates. We test whether the different reproductive strategies of live-bearing rays and egg-laying skates explain this observed paradox by comparing variation in r max with adult body mass, offspring size, temperature, and depth across 85 species of rays and skates. Our results show that the large relative offspring size of warm, shallow-water tropical rays better explains their greater intrinsic sensitivity (lower r max) compared to cold, deep-water temperate skates. This is consistent with life history theory that suggests r max is greater in species with smaller relative offspring size. We hypothesise that the larger relative offspring size may be driven by greater predation risk in the tropics and may help explain global patterns of intrinsic sensitivity to overexploitation.### Competing Interest StatementThe authors have declared no competing interest.

The deep ocean is the last natural biodiversity refuge from the reach of human activities. Deepwater sharks and rays are among the most sensitive marine vertebrates to overexploitation. One-third of threatened deepwater sharks are targeted, and half the species targeted for the international liver-oil trade are threatened with extinction. Steep population declines cannot be easily reversed owing to long generation lengths, low recovery potentials, and the near absence of management. Depth and spatial limits to fishing activity could improve conservation when implemented alongside catch regulations, bycatch mitigation, and international trade regulation. Deepwater sharks and rays require immediate trade and fishing regulations to prevent irreversible defaunation and promote recovery of this threatened megafauna group.

Nations have committed to reductions in the global rate of species extinctions through the Sustainable Development Goals 14 and 15, for ocean and terrestrial species, respectively. Biodiversity loss is worsening despite rapid growth in the number and extent of protected areas, both at sea and on land. Resolving this requires targeting the locations and actions that will deliver positive conservation outcomes for biodiversity. The Species Threat Abatement and Restoration (STAR) metric, developed by a consortium of experts, quantifies the contributions that abating threats and restoring habitats in specific places offer towards reducing extinction risk based on the IUCN Red List of Threatened SpeciesTM. STAR is now recommended as an appropriate metric by recent disclosure frameworks for companies to report their impacts on nature and STAR has seen widespread uptake within the private sector. However, it is currently only available for the terrestrial realm. We extend the coverage of the threat abatement component of the STAR metric (START), used to identify locations where positive interventions could make a large contribution to reducing global species extinction risk and where developments that increase threats to species should be mitigated, to the marine realm for 1646 marine species. Reducing unsustainable fishing provides the greatest opportunity to lower species extinction risk, comprising 43% of the marine START score. Three-quarters (75%) of the global marine START score falls entirely outside the boundaries of protected areas and only 2.7% falls within no-take protected areas. The STAR metric can be used both to guide protected area expansion and to target other actions, such as establishment and enforcement of fishing limits, to recover biodiversity.

Understanding the informal institutions arising from cultural norms, taboos, and beliefs can improve conservation efforts and resource management in Africa. However, little is known of their potential for governing the management of artisanal gillnet fisheries, as well as, the practices and activities of fishers in Ghana. Here, we explore the practices of artisanal gillnet fishers landing shark and ray as their major components and the informal institutions governing the management of these fisheries. We interviewed 33 active and retired fishers in five fishing communities in Western Ghana, complemented with participant observations to collect data for the study. While fishing effort and the financing of fishing trips vary between fishers using drift gillnets and bottomset gillnets, the sharing systems and payment of crew members are relatively uniform in both fisheries and across the study communities. Despite the absence of state regulation, the species-specific taboos recorded offer protection for Whale Shark (Rhincodon typus) and whales (Cetacea), which are considered threatened by the International Union for Conservation of Nature. The role of modern religions (like Christianity and Islam) and the influx of different people with different values, beliefs, and cultures explain the erosion of some resource management taboos and beliefs. The results of this study demonstrate the importance of officially recognizing these informal institutions as legitimate institutions for the effective management of imperiled marine species targeted by gillnet fishers at the local level.

Metabolic morphology—the morphological features related to metabolic rate—offers broad comparative insights into the physiological performance and ecological function of species. However, some metabolic morphological traits, such as gill surface area, require costly and lethal sampling. Measurements of gill slit height from anatomically accurate drawings, such as those in field guides, offer the opportunity to understand physiological and ecological function without the need for lethal sampling. Here, we examine the relationship between gill slit height and each of the three traits that comprise ecological lifestyle: activity, maximum body size, and depth across nearly all sharks (n = 455). We find that gill slit heights are positively related to activity (measured by the aspect ratio of the caudal fin) and maximum size but negatively related to depth. Overall, gill slit height is best explained by the suite of ecological lifestyle traits rather than any single trait. These results suggest that more active, larger and shallower species (and endothermic species) have higher metabolic throughput as indexed by gill slit height (oxygen uptake) and ecological lifestyle (oxygen expenditure). We show that meaningful ecophysiological relationships can be revealed through measurable metabolic morphological traits from anatomically accurate drawings, which offers the opportunity to estimate class-wide traits for analyses of life history theory and the relationship between biodiversity and ecological function.

Across vertebrates, live bearing evolved at least 150 times from ancestral egg laying into diverse forms and degrees of prepartum maternal investment.1,2 A key question is how reproductive diversity arose and whether reproductive diversification underlies species diversification.3,4,5,6,7,8,9,10,11 To test this, we evaluate the most basal jawed vertebrates: the sharks, rays, and chimaeras, which have one of the greatest ranges of reproductive and ecological diversity among vertebrates.2,12 We reconstruct the sequence of reproductive mode evolution across a phylogeny of 610 chondrichthyans.13 We reveal egg laying as ancestral, with live bearing evolving at least seven times. Matrotrophy evolved at least 15 times, with evidence of one reversal. In sharks, transitions to live bearing and matrotrophy are more prevalent in larger-bodied tropical species. Further, the evolution of live bearing is associated with a near doubling of the diversification rate, but there is only a small increase associated with the appearance of matrotrophy. Although pre-copulatory sexual selection is associated with increased rates of speciation in teleosts,3 sexual size dimorphism in chondrichthyans does not appear to be related to sexual selection,14,15 and instead we find increased rates of speciation associated with the colonization of novel habitats. This highlights a potential key difference between chondrichthyans and other fishes, specifically a slower rate of evolution of reproductive isolation following speciation, suggesting different rate-limiting mechanisms for diversification between these clades.16 The chondrichthyan diversification and radiation, particularly throughout shallow tropical shelf seas and oceanic pelagic habitats, appear to be associated with the evolution of live bearing and proliferation of a wide range of maternal investment in developing offspring.

Here, we summarise the extinction risk of the sharks and rays endemic to coastal, shelf, and slope waters of the southwest Indian Ocean and adjacent waters (SWIO+, Namibia to Kenya, including SWIO islands). This region is a hotspot of endemic and evolutionarily distinct sharks and rays. Nearly one-fifth (n = 13 of 70, 18.6%) of endemic sharks and rays are threatened, of these: one is Critically Endangered, five are Endangered, and seven are Vulnerable. A further seven (10.0%) are Near Threatened, 33 (47.1%) are Least Concern, and 17 (24.3%) are Data Deficient. While the primary threat is overfishing, there are the first signs that climate change is contributing to elevated extinction risk through habitat reduction and inshore distributional shifts. By backcasting their status, few endemic species were threatened in 1980, but this changed soon after the emergence of targeted shark and ray fisheries. South Africa has the highest national conservation responsibility, followed by Mozambique and Madagascar. Yet, while fisheries management and enforcement have improved in South Africa over recent decades, substantial improvements are urgently needed elsewhere. To avoid extinction and ensure robust populations of the region’s endemic sharks and rays and maintain ecosystem functionality, there is an urgent need for the strict protection of Critically Endangered and Endangered species and sustainable management of Vulnerable, Near Threatened, and Least Concern species, underpinned by species-level data collection and reduction of incidental catch.

Understanding how growth and reproduction will adapt to changing environmental conditions is a fundamental question in evolutionary ecology, but predicting the responses of specific taxa is challenging. Analyses of the physiological effects of climate change upon life history evolution rarely consider alternative hypothesized mechanisms, such as size-dependent foraging and the risk of predation, simultaneously shaping optimal growth patterns. To test for interactions between these mechanisms, we embedded a state-dependent energetic model in an ecosystem size-spectrum to ask whether prey availability (foraging) and risk of predation experienced by individual fish can explain observed diversity in life histories of fishes. We found that asymptotic growth emerged from size-based foraging and reproductive and mortality patterns in the context of ecosystem food web interactions. While more productive ecosystems led to larger body sizes, the effects of temperature on metabolic costs had only small effects on size. To validate our model, we ran it for abiotic scenarios corresponding to the ecological lifestyles of three tuna species, considering environments that included seasonal variation in temperature. We successfully predicted realistic patterns of growth, reproduction, and mortality of all three tuna species. We found that individuals grew larger when environmental conditions varied seasonally and spawning was restricted to part of the year (corresponding to their migration from temperate to tropical waters). Growing larger was advantageous because foraging and spawning opportunities were seasonally constrained. This mechanism could explain the evolution of gigantism in temperate tunas. Our approach addresses variation in food availability and individual risk as well as metabolic processes and offers a promising approach to understand fish life-history responses to changing ocean conditions.

The true state of ocean biodiversity is difficult to assess, and there are few global indicators to track the primary threat of overfishing. We calculated a 50-year Red List Index of extinction risk and ecological function for 1199 sharks and rays and found that since 1970, overfishing has halved their populations and their Red List Index has worsened by 19%. Overfishing the largest species in nearshore and pelagic habitats risks loss of ecomorphotypes and a 5 to 22% erosion of functional diversity. Extinction risk is higher in countries with large human coastal populations but lower in nations with stronger governance, larger economies, and greater beneficial fisheries subsidies. Restricting fishing (including incidental catch) and trade to sustainable levels combined with prohibiting retention of highly threatened species can avert further depletion, widespread loss of population connectivity, and top-down predator control.

In ecosystems, sharks can be predators, competitors, facilitators, nutrient transporters, and food. However, overfishing and other threats have greatly reduced shark populations, altering their roles and effects on ecosystems. We review these changes and implications for ecosystem function and management. Macropredatory sharks are often disproportionately affected by humans but can influence prey and coastal ecosystems, including facilitating carbon sequestration. Like terrestrial predators, sharks may be crucial to ecosystem functioning under climate change. However, large ecosystem effects of sharks are not ubiquitous. Increasing human uses of oceans are changing shark roles, necessitating management consideration. Rebuilding key populations and incorporating shark ecological roles, including less obvious ones, into management efforts are critical for retaining sharks’ functional value. Coupled social-ecological frameworks can facilitate these efforts.

The maximum intrinsic rate of population increase (rmax) represents a population's maximum capacity to replace itself and is central to fisheries management and conservation. Species with lower rmax typically have slower life histories compared to species with faster life histories and higher rmax. Here, we posit that metabolic rate is related to the fast-slow life history continuum and the connection may be stronger for maximum metabolic rate and aerobic scope compared to resting metabolic rate. Specifically, we ask whether variation in rmax or any of its component life-history traits - age-at-maturity, maximum age, and annual reproductive output - explain variation in resting and maximum metabolic rates and aerobic scope across 84 shark and teleost species, while accounting for the effects of measurement temperature, measurement body mass, ecological lifestyle, and evolutionary history. Overall, we find a strong connection between metabolic rate and the fast-slow life history continuum, such that species with faster population growth (higher rmax) generally have higher maximum metabolic rates and broader aerobic scopes. Specifically, rmax is more important in explaining variation in maximum metabolic rate and aerobic scope compared to resting metabolic rate, which is best explained by age-at-maturity (out of the life history traits examined). In conclusion, teleosts and sharks share a common fast-slow physiology/life history continuum, with teleosts generally at the faster end and sharks at the slower end, yet with considerable overlap. Our work improves our understanding of the diversity of fish life histories and may ultimately improve our understanding of intrinsic sensitivity to overfishing.

The Gill Oxygen Limitation Theory (GOLT) posits that a mismatch in oxygen supply and demand stemming from geometric constraints on gill surface area limits metabolic rate and energy available for biological processes. This theory has been suggested to explain numerous phenomena observed with warming yet is based upon a relationship among maximum size, growth, and gill surface area established over 40 years ago. However, the metric used in this relationship to characterize gill surface area, gill area index, fails to capture the known variability in the scaling of gill surface area and is biased by the sizes at which gills were measured. Here, we revisit a central prediction of the GOLT, asking four key questions that examine limitations in the original relationship. We find that gill area index does indeed explain variation in growth performance across 132 species of fish and this relationship is strikingly similar to the original relationship across 42 species. Yet, we argue that gill area index is not an adequate measure of gill surface area because (1) it has a non-linear relationship with size and, thus, changes ontogenetically as an individual grows over time and (2) because it is based on mean estimates of both gill surface area and body mass. Indeed, we show that the value of gill area index for a given species is variable depending on how it is calculated. We therefore suggest a pathway forward for assessing whether gill surface area is an important factor in explaining variation in growth performance.

Life history theory suggests that maximum size and growth evolve to maximize fitness. In contrast, the Gill Oxygen Limitation Theory (GOLT) suggests that growth and maximum size in fishes and other aquatic, water-breathing organisms is constrained by the body mass-scaling of gill surface area. Here, we use new data and a novel phylogenetic Bayesian multilevel modelling framework to test this idea by asking the three questions posed by the GOLT regarding maximum size, growth and gills. Across fishes, we ask whether the body mass-scaling of gill surface area explains (1) variation in the von Bertalanffy growth coefficient (k) above and beyond that explained by asymptomatic size (W-8), (2) variation in growth performance (a trait that integrates the tradeoff between k and W-8) and (3) more variation in growth performance compared to activity (as approximated by caudal fin aspect ratio). Overall, we find that there is only a weak relationship among maximum size, growth and gill surface area across species. Indeed, the body mass-scaling of gill surface area does not explain much variation in k (especially for those species that reach the same W-8) or growth performance. Activity explained three to five times more variation in growth performance compared to gill surface area. Our results suggest that in fishes, gill surface area is not the only factor that explains variation in maximum size and growth, and that other covariates (e.g. activity) are likely important in understanding how growth, maximum size and other life history traits vary across species.