New research finds more than half of reef sharks and rays threatened with extinction

More than half of known species of coral reef sharks and rays are threatened with extinction, according to new research that underscores the urgent need for improved regional fisheries and marine protected areas management.

The study, published on January 17 in the journal Nature Communications, identified 79 of the world’s 134 coral reef-associated rays and sharks — also known as chondrichthyans — as being in one of the threatened categories on the IUCN Red List. Overfishing appears to be the biggest cause for the population decline, followed by climate change, habitat loss and degradation, residential and commercial development, and pollution, the study authors said.

“There are few policies that have been put in place to manage reef sharks and rays,” lead author Samantha Sherman, a postdoctoral research fellow at Simon Fraser University in Canada, told Mongabay in an email interview.
“These species are difficult to manage as they occur mainly in countries with very high coastal populations that rely on resources from the ocean for food and earning money to support their families,” she added. “These countries also tend to have large numbers of small boats and small markets spread throughout the coast, which makes implementation of any policies difficult.”

The authors, who according to Sherman are mostly members of the IUCN’s Shark Specialist Group, developed a Red List Index to track the progress toward international biodiversity targets over the past half century. They found 14 species fit the “critically endangered” category, making them nearly extinct in the wild; 24 species were “endangered,” which indicates population reduction of 50-70% in the past three generations; and 41 species belonged in the “vulnerable” status as their population had declined by around 20-50% in the past three generations.

The authors also reported that population trends were declining for 94 coral reef shark and ray species; of the two groups, rays were more threatened than sharks. “Despite this risk, there are very few limitations on the catch and landing of rays,” Sherman said.

The study identifies the coral reefs of northern Australia and Southeast Asia as having the richest population of both sharks and rays. Notably, the authors found that sharks faced the most threat in the western Atlantic, while rays were most vulnerable across Asia and southeast Africa. Locations like the Pacific islands, where reef sharks and rays are quite abundant, could serve as refuges for threatened, widespread species, making them key to regional and global conservation efforts, according to the study.

A gray reef shark (Carcharhinus amblyrhynchos). The species’ population has declined within Australia’s Great Barrier Reef Marine Park, largely due to illegal fishing. Image by Albert Kok via Wikimedia Commons (Public domain).

The extinction risk is highest for widely distributed large species, such as the bull shark (Carcharhinus leucas) and reef manta ray (Mobula alfredi), both found in the waters of more than 60 countries. The risk is also particularly pronounced in countries with higher fishing pressure and weaker governance, such as Brazil, Tanzania and Indonesia, according to the study.

Reef sharks and rays are typically caught for human consumption, and to a lesser extent for their body parts, which are used in making apparel or accessories. Other uses include as aquarium display, feed for domestic animals, and in traditional medicine.
The authors call for better control and management across all scales of fisheries to achieve population recovery, coupled with strong enforcement and effective marine protected areas at regional and global levels of government. In addition, improving education and diversification of rural livelihoods in regions with overexploited reefs could help reduce fishing pressure on threatened species.

“Lots of reef species occur in many countries, meaning conservation efforts require global cooperation,” Sherman said, also noting that international trade regulations for sharks and rays that are meant to protect them still lack effective implementation and thus fall short in tackling the problem of bycatch-related deaths.

Without broad-scale action to improve the status of reef sharks and rays, the authors say, their populations will continue to decline with increasingly dire consequences for the ecosystem health of coral reefs and coastal communities whose livelihoods depend on them.
“The findings are being communicated by all the co-authors and others that work in the field to relevant governments they already work with to make the case for greater action to conserve these species,” Sherman said.

Failure to address these threats immediately can already be seen in several reefs across the world where shark populations have declined to a level considered to be “functionally extinct” from these ecosystems. Sharks are apex predators that target sick and weak fish, leaving the stronger ones to reproduce, thus contributing to the maintenance of a healthy marine ecosystem.
“There are many interesting facts about sharks and rays, but I would like to highlight stingrays, as people don’t hear about them often,” Sherman said. “Stingrays act as ecosystem engineers because when they feed, they create pits in the sand called ‘feeding pits.’ When the tide goes out, some pits will hold water and provide a place for small fish and other animals to hide from bigger predators.”

Citation:

Sherman, C. S., Simpfendorfer, C. A., Pacoureau, N., Matshushiba, J. H., Yan, H. F., Walls, R. H. L., … Dulvy, N. K. (2023). Half a century of rising extinction risk of coral reef sharks and rays. Nature Communications. doi:10.1038/s41467-022-35091-x.

The author of this article, Basten Gokkon is a senior staff writer for Indonesia at Mongabay.
Find him on Twitter @bgokkon.
The original article has been published on Mongabay, a U.S.-based non-profit conservation and environmental science news platform, under a Creative Commons Attribution-NoDerivatives 4.0 International License, here: More than half of reef sharks and rays threatened with extinction, study shows.

The cover image, in the public domain, is a photo taken by Kevin Lino for the U.S. National Oceanic and Atmospheric Administration.