An alarming new study examining sawfish records has found that these shark-like rays have been lost in half of the world’s coastal waters and are on course to be wiped out, predominantly due to overfishing.
A team of researchers from Simon Fraser University in British Columbia, Canada, said the animals were once found along the coastlines of 90 countries but they are now among the world's most threatened family of marine fishes, and are presumed extinct from 46 of those nations.
There are 18 countries where at least one species of sawfish is missing, and 28 more where two species have disappeared.
There are five species of sawfish in total, and three of these are now critically endangered, while the other two are listed as endangered, according to the International Union for Conservation of Nature (IUCN) Red List of Threatened Species.
The species are named after their unusual long, narrow noses, called rostra, which are banded with an external wreath of teeth, bearing resemblance to a saw blade.
The fish are among the largest in the ocean with some species reaching lengths of about up to 7.6 metres (25 feet).
They use their saw to detect and monitor the movements of smaller prey by measuring the electric fields they emit, before then attacking using the saw either to lacerate victims, or pin them down on the seabed, before eating them.
However, the teeth on their rostra are easily caught in fishing nets. Sawfish fins are among the most valuable in the global shark fin trade and rostra are also sold for novelty, medicine and as spurs for cockfighting.
The current presence of all sawfishes world-wide is unknown, but SFU researcher Nick Dulvy warns complete extinction is possible if nothing is done to curb overfishing and to protect threatened habitats, such as mangroves, where sawfish can thrive.
“Through the plight of sawfish, we are documenting the first cases of a wide-ranging marine fish being driven to local extinction by overfishing,” Professor Dulvy said.
“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.”
He added: “With this study, we tackle a fundamental challenge for tracking biodiversity change: discerning severe population declines from local extinction.”
The study recommends that international conservation efforts focus on eight countries: Cuba, Tanzania, Columbia, Madagascar, Panama, Brazil, Mexico and Sri Lanka.
This is where the researchers suggest conservation efforts and adequate fishing protections could save the species.
The study said Australia and the United States, where “adequate protections already exist” and some sawfish are still present, should be considered “lifeboat” nations.
“While the situation is dire, we hope to offset the bad news by highlighting our informed identification of these priority nations with hope for saving sawfish in their waters,” said SFU research assistant Helen Yan.
“We also underscore our finding that it's actually still possible to restore sawfish to more than 70 per cent of their historical range, if we act now.”
The research is published in the journal Science Advances.
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