GLOBAL STUDY FINDS SAWFISHES SLIDING CLOSER TO EXTINCTION

Global study finds sawfishes sliding closer to extinction. Scientists examine risks to world’s largest rays, identify where they’re gone and where there’s still hope.

A ground breaking analysis published in Science Advances today offers a global assessment of the serious extinction risk facing the world’s sawfishes. These large, shark-like rays have been presumed locally extinct in more than half of their historical coastal range. Authors used dynamic geography theory to estimate extinction risk in 42 nations where status was uncertain and concluded that sawfish are extinct in nine. Another eight nations, which have the low fishing pressure and ample habitat needed to give sawfish a chance, are proposed as priorities for research and protections.

“Through the plight of sawfish, we are documenting the first cases of a wide-ranging marine fish being driven to local extinction by overfishing,” said co-author Nick Dulvy, professor at Simon Fraser University (SFU). “We’ve known for a while that the dramatic expansion of fishing is the primary threat to ocean biodiversity, but robust population assessment is difficult for low priority fishes whose catches have been poorly monitored over time. With this study, we tackle a fundamental challenge for tracking biodiversity change: discerning severe population declines from local extinction.”

Like other rays and closely related sharks, sawfishes are particularly vulnerable to over exploitation because of low reproductive rates. Once found in the coastal waters and rivers of more than 90 tropical and subtropical countries, all five species are now classified as Endangered or Critically Endangered on the IUCN Red List. Fishing is the main threat to sawfish. Their saws (“rostra”) are easily entangled in nets. Destruction of key habitats, particularly mangroves, also poses a threat.

“We estimate that sawfish are gone from 55 of the 90 nations where they were once found – completely and tragically lost from an area that amounts to nearly 60% of their former range,” said Helen Yan, lead author and researcher at SFU. “While the situation is dire, we hope to offset the bad news by highlighting our informed identification of eight priority nations with hope for saving sawfish in their waters. We also underscore our finding that it’s actually still possible to restore sawfish to more than 70% of their historical range, if we act now.”

Restrictions on fishing offer the greatest benefit to sawfishes. Minimising the mortality of sawfish due to fishing can reduce extinction risk by up to 20.7% globally. Doubling mangrove area can reduce extinction risk by 10.1%, though benefits vary by country. The authors urgently recommend national bans on killing and retaining sawfish as well as programmes to prevent sawfish catches, maximise post-release survival, and protect habitats, particularly mangroves.

“Because of decades of steadily increasing attention to sawfish from scientists and conservationists, public understanding and appreciation is way up. In too many places, however, we’re running out of time to save them,” said Sonja Fordham, co-author and President of Shark Advocates International, a project of The Ocean Foundation. “With new scientific and policy tools, the opportunities to turn the tide for sawfish are better than ever yet fleeting. We’ve highlighted the actions that can bring these extraordinary animals back from the brink. We mainly just need governments to step up, before it’s too late.”

Photo credit: Tonya Wiley