Half a century of rising extinction risk of coral reef sharks and rays

Abstract

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.

Fig. 1. The percent of coral reef species in the IUCN Red List categories.

Red lines indicate the best estimate of threat assuming all Data Deficient (DD, grey shade) species faced a similar level of threat to the data-sufficient species in the taxon. Extinct (EX), Critically Endangered (CR), Endangered (EN), Vulnerable (VU), Near Threatened (NT), and Least Concern (LC). Source data are provided as a Source Data file.

Fig. 2. High extinction risk of coral reef sharks and rays due to exposure to overfishing and other threatening processes combined with sensitive life histories.

a IUCN Threat classification for coral reef species. Percent of coral reef shark and ray species in each IUCN category by b residency patterns, and c trophic positions. The effects of d maximum body size, e geographic range size (indexed by number of nations a species occurs in), and (f) lower depth limit on the probability that a data-sufficient reef shark or ray species is listed as either Critically Endangered (CR), Endangered (EN), Vulnerable (VU), Near Threatened (NT), or Least Concern (LC) based on cumulative link mixed-effects models. Source data are provided as a Source Data file.

Fig. 3. National attributes also explain extinction risk.

Variable importance for explaining proportion of threatened species of all covariates across 1,000 bootstrapped boosted regression tree models for a sharks and b rays. The marginal effect c–n of each variable on the proportion of threatened species for rays and sharks ordered by variable importance. Explanatory variables were all scaled and centred around zero for presentation purposes; raw values were used in the analysis. Explanatory variables include: c sea surface temperature, d catch-per-unit-effort (CPUE), e shelf area, f primary production, g coastal population, h Gross Domestic Product (GDP), i marine protein consumption, j World Governance Index (WGI), k fishing effort, l catch, m sightings-per-unit-effort (SPUE), and n Human Development Index (HDI).

Fig. 4. Global shark and ray species richness, threat, and proportion threatened by group.

a, e species richness by group. b, f number of threatened species by group. c, g threatened species as a proportion of total richness (for cells with >5 species) by species group. a–d sharks and e–h rays. Scale bar: 5000 km. d, h histograms represent the number of grid cells containing different percentages of threatened species.

Fig. 5. Increase in extinction risk of coral reef sharks and rays over the past half century.

Global Red List index (RLI) for the 125 data-sufficient reef sharks and rays combined, and each separately, estimated in 1970, 1980, 2005, and 2021, and compared to the RLI for all shark and ray species. An RLI value of 1 indicates that all species in the taxa are Least Concern and an RLI value of 0 indicates that all species are Extinct. Source data are provided as a Source Data file.