Colin A. Simpfendorfer

The reopening of the Maldivian gulper shark ( Centrophorus spp.) fishery highlights the need for precautionary management under substantial uncertainty. Gulper sharks are among the least productive and most vulnerable marine species, with extremely slow recovery following overexploitation. Although reopening without evidence of recovery poses clear conservation risks, the precautionary principle is insufficiently operationalised in a proposal to use Environmental DNA (eDNA) to inform management, lacking defined reference points, recovery thresholds, or harvest control rules. eDNA, as currently applied, cannot meet the evidentiary requirements of precautionary fisheries management, as it provides presence‐only information and cannot reliably indicate abundance, population structure, or recovery. eDNA should therefore complement, not replace, robust baseline data, species‐specific assessments and explicit decision rules.

The International Union for Conservation of Nature (IUCN) Red List of Threatened Species is a critical measure of global aquatic and terrestrial biodiversity status. It is also the basis for the Red List Index, which tracks extinction risk over time. Sharks, rays, and chimaeras (Chondrichthyes) have now been comprehensively assessed twice (1996–2011 and 2012–2021) with hindcast assessments from 1970 onward, yielding an unprecedented extinction risk trajectory for an aquatic vertebrate class. The three‐decade success of the IUCN Species Survival Commission (SSC) Shark Specialist Group (SSG) in providing updated and evidence‐based assessments stems from sustained and coordinated activities by SSG members. We examined how a community of dedicated experts organized to fill gaps in key information to inform Red List assessments. From this evaluation, we identified six key lessons related to membership, taxonomic changes, implementation of the precautionary approach, information prioritization, assessment standardization, and policy efforts. However, existing challenges, including resource constraints and assessment discrepancies at different spatial scales, need to be addressed to ensure Red List assessments stay on pace with advances in conservation. With the second global assessment of chondrichthyans completed, it is appropriate to reflect on the evolution of the SSG and its achievements over three decades to highlight new tools and approaches to red listing and to identify priorities for the immediate future that are also applicable to other aquatic taxa with limited data, slow life histories, and exposure to high levels of fishing.

Understanding migratory connectivity is important for the conservation of highly mobile marine species that face escalating threats across the globe. Establishing baseline information on migratory connectivity is therefore needed to identify regions of conservation focus. Despite efforts to track migratory sharks and rays, information on transboundary movements is limited and often inaccessible to managers and policymakers. Here, we synthesised multimethod movement data for migratory Australian shark and ray species, investigating which species require international engagement to support their population recovery. Based on data from a systematic literature review, we built connectivity networks from telemetry and mark-recapture studies that provide a first baseline for transboundary migratory connectivity for Australian sharks and rays. Of the 31 shark and ray species reviewed, we identified 6 species that link the Australian Exclusive Economic Zone to other national jurisdictions via multispecies migratory connections through the Tasman Sea to New Zealand, through the Tasman and Coral Sea to New Caledonia, and north across the Timor Sea and Torres Strait to Indonesia and Papua New Guinea. White sharks ( Carcharhinus carcharias ) and whale sharks ( Rhincodon typus ) were the most data rich, whereas 14 shark and ray species had no movement information. There is a grave deficiency in available information for endangered or critically endangered migratory shark and ray populations, with 76% having only one or no published studies. This work supports future conservation strategies for migratory sharks that require robust international collaboration and the adoption of integrated and dynamic management approaches.

Environmental DNA (eDNA) analysis is becoming a valuable conservation tool for detecting rare and threatened species in a variety of aquatic environments, but studies in freshwater and estuarine habitats with high levels of suspended sediment are still limited. This study used a large-scale eDNA survey to test for the presence of the Critically Endangered largetooth and smalltooth sawfishes Pristis pristis and P. pectinata in Costa Rica. Specifically, we used species-specific TaqMan quantitative PCR assays to test for the presence of both sawfish species in freshwater, estuarine, and marine habitats through a nationwide survey using standardized field and laboratory protocols developed by the Global Sawfish Search Project (James Cook University, Australia). A total of 558 samples were collected from 18 sites, 93 stations, and 6 geographic regions; 486 samples were used to test for P. pristis, 55 samples were used to test for P. pectinata, and 93 were included as negative controls. P. pristis was detected in 16 samples collected from the northern and north Caribbean regions of Costa Rica; however, there were no detections of P. pectinata. Our eDNA survey provides the first indirect evidence for the presence of P. pristis in fast-flowing freshwater habitats with high levels of suspended sediment in Costa Rica. Based on our findings, the San Juan-Colorado River basin, a natural border between Costa Rica and Nicaragua, is a key region in Central America to guide future conservation efforts for the recovery of P. pristis.

Human–wildlife conflicts (HWCs) are increasing globally and are some of the most pervasive problems for the conservation of terrestrial and marine species. Stakeholders often hold different values and concerns surrounding HWCs, and understanding these values and their relative importance among stakeholders allows for more effective decision‐making. We developed a multi‐objective decision analysis framework to compare and assist in determining preferred mitigation measures to reduce HWCs. We illustrate how this framework can be used to identify appropriate mitigation measures to reduce the risk of shark bites, which have been increasing worldwide and have led to ongoing controversy and debate between governments and other stakeholders. We combined expert assessment of shark‐bite mitigation measures against socio‐economic and environmental criteria, while accounting for subjective ranking of the importance of these performance criteria across stakeholders. Our flexible framework was tested to compare 15 mitigation measures for the Gold Coast region of Queensland, Australia, using 12 performance criteria. Results reiterated the societal shift towards non‐lethal measures and highlighted which mitigation measures or performance criteria lacked information, helping to identify knowledge gaps and research needs. The flexibility of our framework makes it applicable to a broad range of contexts and HWCs and allows the incorporation of location‐specific requirements and views that may vary between stakeholders. Read the free Plain Language Summary for this article on the Journal blog.

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.

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

The 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.