Reef sharks at much higher risk of extinction than previously thought

The five main shark species that live on coral reefs — grey reef, blacktip reef, whitetip reef, nurse and Caribbean reef shark - have declined by an average of 63 percent worldwide, according to the scientists after a five-year international study funded by the Paul G. Allen Family Foundation. The results were published last week in Science.

"This study provides a good picture of the population decline of reef sharks worldwide because of the very large number of reefs and countries examined," said Twan Stoffers, researcher within the Aquaculture and Fisheries group at Wageningen University & Research, and one of the many researchers who collaborated on this large-scale study. "The results of this study tell us that the problem for sharks on coral reefs is much bigger than anyone thought."

Results from this latest research, which includes 22,000 hours of video footage from baited underwater video stations across 391 reefs in 67 nations and territories, indicate that widespread overfishing is the main culprit driving reef sharks toward extinction.

Sharks and rays are originally common in tropical coral reefs. But as these reefs become more heavily fished, both shark and rays are lost, depending on the size of the fishery and the methods used. Often a reef with elevated fishing pressure is dominated by rays, which can lead to a disruption of the food web. Loss of sharks can also have serious impact on the overall health and function of coral reef ecosystems.

Although overfishing and poor reef management are associated with the absence of sharks and rays, they are still common in marine protected areas (MPAs) and on reefs where shark fishing was prohibited or highly regulated, this study shows. Stoffers clarifies: "We see this in the Caribbean Netherlands, among others areas, where the territorial waters and thus the reefs around Bonaire, Saba and St Eustatius are an MPA. It is precisely here that relatively high numbers of sharks and rays can still be found. Also, there has traditionally been little fishing for these species here. This may be another reason the Caribbean Netherlands still scores quite well in this study when it comes to the occurrence of sharks and rays."

Early results of the study were previously used to adjust the status of four of the listed shark species to more endangered categories on the International Union for the Conservation of Natures (IUCN) Red List. They were also presented at the most recent Conference of the Parties of the Convention at the International Trade in Endangered Species of Wild Fauna and Flora (CITES), helping world governments to make the groundbreaking decision to better regulate trade in these and more than 50 additional species of shark species.

"This means that trade should not take place from countries where fishing of the species poses a threat to its survival," Stoffers said. "Our study can be used to determine in which countries fishery of sharks would be harmful. We must act now to stop the global extinction of sharks."

More than 150 researchers, including Wageningen University & Research, and more than 120 institutes worldwide contributed to this study.