Tunas, Billfishes Recover Yet Sharks’ Extinction Risk Rises

Although some tunas and billfishes are recovering after decades of decline from overfishing, due in large part to successful fisheries management and conservation actions, shark biodiversity continues to decline, according to a new study evaluating yearly changes in these species’ extinction risk for the last 70 years. The findings simultaneously illustrate the value of conservation and management in protecting large ocean species and underscore the immediate need for these protections to be extended to sharks.

It’s estimated that intense fishing across the planet’s oceans has led to roughly half of all commercially harvested fish and invertebrate stocks becoming overfished during the 20^th century, including iconic large predatory fishes like tuna, billfishes, and sharks. However, while intense fishing activity has been increasingly monitored and managed, its overarching effects on ocean biodiversity are generally poorly understood.

Based on International Union for Conservation of Nature (IUCN) Red List categories and criteria, Maria José Juan-Jordá and colleagues created a continuous Red List Index (RLI) of yearly changes in extinction risk of oceanic tunas, billfishes, and sharks spanning the last 70 years to better understand the health of oceanic biodiversity as well as the overall impacts of fishing mortality and conservation efforts on these populations. Juan-Jordá et al. found that after more than half a century of increasing risk of extinction due to increasing fishing pressure, effective fisheries management and conservation strategies have allowed populations of tuna and billfish to recover over the past decade. However, the extinction risk for sharks, which remain largely undermanaged, continues to rise. The findings suggest that while target species are increasingly and successfully sustainably managed to ensure maximum catch, other functionally important species like sharks, which are often captured as bycatch in these fisheries, continue to decline because of insufficient management actions.

“The conservation statuses of threatened target species can be improved by managing the fishing industry, which can benefit the industry economically in the long run while allowing the threatened species to recover,” write Matthew Burgess and Sarah Becker in a related Perspective. “However, the protection of high-vulnerability bycatch and nontarget species is expected to be more difficult because they will require fisheries to invest in better fishing gear and targeting practices, or reduce fishing efforts, without directly benefiting from these changes.”

- This press release was provided by the American Association for the Advancement of Science