Several reef sharks at greater threat of extinction than thought, study shows

A new study found that five key reef shark species — gray, blacktip, whitetip and Caribbean reef sharks, and nurse sharks — declined by 60-73% worldwide.
It also indicated that all five species would qualify as endangered on the IUCN Red List.
Early results from the study were used to escalate the status of two of the five species to endangered, but the others are still considered to have a lower extinction risk.
The study also showed that well-governed or protected reefs had healthier shark populations.

New research has found that five key shark species found in reef habitats are at higher risk of extinction than previously thought, mainly due to overfishing.

Published in Science, the study indicates that gray reef sharks (Carcharhinus amblyrhynchos), blacktip reef sharks (Carcharhinus melanopterus), whitetip reef sharks (Triaenodon obesus), nurse sharks (Ginglymostoma cirratum) and Caribbean reef sharks (Carcharhinus perezi) declined by 60-73% across the world. As these sharks have disappeared from reefs, rays have begun to take over, except in places where both sharks and rays are being depleted, according to the study.

This research builds upon a 2020 study in Nature that found that sharks were “functionally extinct” from about 20% of the world’s coral reefs.

“That [Nature] study basically grouped all of the sharks that occur on coral reefs together in one group and looked at what was going on,” Colin Simpfendorfer, lead author of the new study and adjunct professor of marine and aquaculture science at James Cook University in Australia, told Mongabay. “What we’ve done with this study is we’ve actually broken it down into individual species so we could look at what is happening to communities of sharks and rays.”

A reef shark visiting a baited underwater video station in the Caribbean. Image by Global Fin Print.

Early results of the study were used to update the status of four of the shark species on the IUCN Red List: the gray reef shark and Caribbean reef shark are now listed as endangered, and the blacktip reef shark and the whitetip reef shark are listed as vulnerable. However, the study indicates that all five of the main shark species would actually qualify as endangered on the IUCN Red List.

“We’ll be continuing to work with [the IUCN] to see if we can get these other ones updated to endangered as well,” Simpfendorfer said.

The results of this study were based on 22,000 hours of video footage from baited underwater video stations at 391 reef locations in 67 nations and territories. The authors found that fishing was the main reason for declining reef shark species.

“Sharks have a very vulnerable life history,” Simpfendorfer said. “They don’t reproduce very quickly, and so when you start to fish them out, they decline very quickly and recover very slowly.”

While the study indicates a sharp decline in reef shark species, it also shows that reefs protected or governed with strong fisheries management had healthier shark populations. The study also notes that an overfished reef at one location doesn’t necessarily impact other reefs a short distance away.

“People need healthy coral reefs,” Mike Heithaus, co-author of the study and executive dean of the College of Arts, Sciences & Education at Florida International University, said in a statement. “We are seeing that when sharks disappear, that causes other changes in these ecosystems. Keeping shark populations healthy, or rebuilding them, is important for maintaining their roles for healthy reefs.”

Banner image caption: A blacktip reef shark swims among smaller fish in the Maldives. Image by Peter Smithson via Flickr (CC BY-NC-SA 2.0).

Elizabeth Claire Alberts is a senior staff writer for Mongabay. Follow her on Twitter @ECAlberts

Sharks are ‘functionally extinct’ in many global reef systems, study finds

Citations:

Simpfendorfer, C. A., Heithaus, M. R., Heupel, M. R., MacNeil, M. A., Meekan, M., Harvey, E., … Chapman, D. D. (2023). Widespread diversity deficits of coral reef sharks and rays. Science, 380(6650), 1155-1160. doi:10.1126/science.ade4884

MacNeil, M. A., Chapman, D., Heupel, M., Simpfendorfer, C. A., Heithaus, M., Meekan, M., … Cinner, J. E. (2020). Global status and conservation potential of reef sharks. Nature, 583(7818), 801-806. doi:10.1038/s41586-020-2519-y

Endangered, Endangered Species, Fish, Fisheries, Fishing, Marine Animals, Marine Conservation, Marine Ecosystems, Overfishing, Sharks, Sharks And Rays, Species