Previous studies have documented local overfishing of some populations of sharks and rays. But this is the first one to survey their status through out coastal seas and oceans. It reveals that one-quarter (249) of 1,041 known shark, ray and chimaera species globally fall under three threatened categories on the IUCN Red List.
A quarter of the world’s sharks and rays face extinction
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"We now know that many species of sharks and rays, not just the charismatic white sharks, face extinction across the ice-free seas of the world," says Dulvy. "There are no real sanctuaries for sharks where they are safe from overfishing."
Sharks and rays are at substantially higher risk of extinction than many other animals and have the lowest percentage of species considered safe. Using the IUCN Red List, the authors classified 107 species of rays (including skates) and 74 species of sharks as threatened. Just 23 percent of species were labeled as being Least Concern.
"In the most peril are the largest species of rays and sharks, especially those living in relatively shallow water that is accessible to fisheries. The combined effects of overexploitation -- especially for the lucrative shark fin soup market -- and habit degradation are most severe for the 90 species found in freshwater.
"A whole bunch of wildly charismatic species is at risk. Rays, including the majestic manta and devil rays, are generally worse off than sharks. Unless binding commitments to protect these fish are made now, there is a real risk that our grandchildren won't see sharks and rays in the wild."
The IUCN SSG is calling on governments to safeguard sharks, rays and chimaeras through a variety of measures, including the following: prohibition on catching the most threatened species, science-based fisheries quotas, protection of key habitats and improved enforcement.
Overfishing is the main threat to the species, according to the paper. Reported catches of sharks, rays and chimaeras peaked in 2003 and have been dominated by rays for the last 40 years. Actual catches are likely to be grossly under-reported.
The global market for shark fins used in shark fin soup is a major factor in the depletion of not only sharks but also some rays with valuable fins, such as guitarfish. Sharks, rays and chimaeras are also sought for their meat. Other products from these species include a Chinese tonic made from manta and devil ray gills and pharmaceuticals made from deep sea shark livers.
The results paint an ominous picture for the chondrichthyan fishes (sharks, rays, and chimaeras) around the world. Only 23% of these species are considered safe from extinction. This makes them the most threatened group of vertebrate animals. This is particularly alarming considering the huge ecological value of these predators, which play a crucial role in the functioning of marine food webs.
In November last year, the South African National Plan of Action for the Conservation and Management of Sharks was announced. This is essentially the national shark conservation guidebook. It provides information on the status of chondrichthyans in South Africa and examines how best to manage shark fishing and the trade of shark products in the South African context. Conservation plans like these, informed by Red List assessments, are crucial for the continued existence of sharks, rays and chimaeras and healthy functioning of marine ecosystems.
The risk of the extinction of these iconic animals not only jeopardizes the health of ocean ecosystems but those who rely on the sea for sustenance. According to the new study, fishing pressure has doubled and catches have tripled, amounting to an 18-fold increase in Relative Fishing Pressure (exploitation relative to the number of fish left). That means fish stocks are decreasing throughout most of the world and food security is no longer guaranteed for many. The authors all call for strict, enforceable regulations in all oceans including area-appropriate fisheries science recommendations and management. Enforcement is also needed for any targets or policies passed; for example, the UN Sustainable Development Goals and specific Aichi Biodiversity Targets (to reverse population declines and use marine resources sustainably) for the year 2020 were not met for these species.
Dr. Marshall said it best: we need to take immediate action to curb the various anthropogenic threats sharks and rays face. We are passing the point of no return and soon we may lose these important animals. Will our children or our grandchildren get to grow up in a world where they exist, or will they be just another extinct animal we see in a book?
Sharks and rays are key functional components of coral reef ecosystems, yet many populations of a few species exhibit signs of depletion and local extinctions. The question is whether these declines forewarn of a global extinction crisis. We use IUCN Red List to quantify the status, trajectory, and threats to all coral reef sharks and rays worldwide. Here, we show that nearly two-thirds (59%) of the 134 coral-reef associated shark and ray species are threatened with extinction. Alongside marine mammals, sharks and rays are among the most threatened groups found on coral reefs. Overfishing is the main cause of elevated extinction risk, compounded by climate change and habitat degradation. Risk is greatest for species that are larger-bodied (less resilient and higher trophic level), widely distributed across several national jurisdictions (subject to a patchwork of management), and in nations with greater fishing pressure and weaker governance. Population declines have occurred over more than half a century, with greatest declines prior to 2005. Immediate action through local protections, combined with broad-scale fisheries management and Marine Protected Areas, is required to avoid extinctions and the loss of critical ecosystem function condemning reefs to a loss of shark and ray biodiversity and ecosystem services, limiting livelihoods and food security.
Chondrichthyans (hereafter, sharks and rays) are a phylogenetically diverse and ecologically important megafaunal lineage on coral reefs. There are 30 families, 59 genera, and 134 species of reef-associated sharks and rays11,12, each with varying degrees of coral-reef association; from residents that spend their entire lives at one or a few reefs (e.g. Halmahera epaulette shark, Hemiscyllium halmahera12), partial residents that spend most of their time on reefs (e.g. Australian weasel shark, Hemigaleus australiensis13), and those transient passing through reef habitats (e.g. Javanese cownose ray, Rhinoptera javanica11). These species fill a range of ecological niches, including: filter feeders, benthic invertivores, resident piscivorous mesopredators, transient apex predators, and more14,15. As highly mobile predators, some species are important nutrient vectors and controllers of primary production16, while others influence primary production through fear-induced trophic cascades17. Here are four examples of nutrient vectoring and cycling. First, grey reef shark (Carcharhinus amblyrhynchos) derives >80% of its diet from pelagic fishes then transfers these nutrients onto reefs16. Similarly, reef manta rays (Mobula alfredi) feed primarily on pelagic zooplankton and transfer these nutrients onto the reef during the day, acting as vectors for horizontal and vertical nutrient transport18. Stingrays are important ecosystem engineers, bioturbating large stretches of soft sediment while feeding or burying themselves in sand19,20. Finally, larger transient apex predators, like the tiger shark (Galeocerdo cuvier) mediate ecosystem structure and function of seagrass beds through fear-induced changes in grazing behaviour of turtles and dugongs17,21, which may be a stronger effect than direct predation22.
Here, we answer this question with the recently completed International Union for Conservation of Nature (IUCN) Red List of Threatened Species reassessment of sharks and rays28. Specifically, we provide a comprehensive assessment of the extinction risk of all 134 coral reef associated shark and ray species and compare their status with all other 4918 coral reef species assessed using IUCN Red List Categories and Criteria. Second, we identify the key threatening processes using (i) the IUCN threat classification scheme28, combined with (ii) species-level29 and (iii) national-level trait-based vulnerability analyses30. Third, we develop an IUCN Red List Index to track the progress toward international biodiversity targets over the past half century31.
We found that the national attributes associated with variations in extinction risk differed between coral reef sharks and rays. For both sharks and rays, the national percentage of globally threatened species was associated mainly with abiotic factors related to population size [sharks: 50.2%, rays 46.6% of the summed average variable importance (AVI)], followed by fishing pressure (27.1% and 43.5%, respectively), and management capacity (22.6% and 9.9%, respectively; Fig. 3a, b; Supplementary Notes; Supplementary Fig. 3).
Sea surface temperature had the highest overall association with shark and ray extinction risk, with a greater importance for rays (32.4% AVI) than sharks (19.8% AVI; Fig. 3c), possibly indicating a latitudinal effect, where there are fewer threatened species in more tropical waters. Primary production was the second most important variable for sharks with a decreased extinction risk with increasing primary production (15.3% AVI), possibly due to increased population sizes resulting from carrying capacity and prey availability (Fig. 3f)26. National catch-per-unit-effort (CPUE) of reef-associated species was the second most important variable for rays (19.2% AVI) such that at very low CPUE, rays had a lower extinction risk and a slight increase in CPUE was associated with a rapid increase in extinction risk (Fig. 3d). The extinction risk of sharks was greatest in nations with larger coastal human populations, and this was the most important predictor for sharks from the fishing pressure variables (12.3% AVI), although it had little importance for rays (2.8% AVI; Fig. 3g). The level of marine protein consumption was moderately important for sharks and rays (9.1 and 6.4%, respectively), but had a counterintuitive relationship with their extinction risk; shark extinction risk decreased with an increase in marine protein consumption, whereas ray risk increased (Fig. 3i). World Governance Index (WGI) and Human Development Index (HDI) did not have strong influence on reef shark or ray extinction risk (Fig. 3j, n), indicating that even nations with higher governance capacity are not always translating this into conservation success for sharks and rays. 2ff7e9595c