Science

Declining shark populations leave “growing hole” in ocean life

Overfishing has inflicted over 70% population losses of some sharks and rays over the past half century, leaving a “gaping and growing hole” in ocean life, according to a study released Wednesday.

The decline of some species, such as the hammerhead shark or manta ray, is remarkable. Among the most affected is the oceanic shark, which is on the verge of extinction.

Prized by fishermen for its fins, it is also a victim of non-selective fishing techniques. Its population has fallen by 98% in 60 years.

“It is a decline worse than that of most large land mammals, and close to or equal to that of the blue whale,” Professor Nick Dulvy, from the Department of Biological Sciences at Canadian Simon University, told AFP. Fraser.

His team collected and analyzed the data allowing them to draw up an overall status of 31 species of sharks and rays.

They conclude that three quarters of the species studied are threatened with extinction.

“We knew that the situation was bad in many places but it came from several studies and reports, so it was difficult to have an idea of ​​the overall situation”, explains to AFP the scientist Nathan Pacoureau, who co-signed the study published in Nature.

“We are showing sharp declines and a rapidly increasing risk of extinction for large species in the planet’s largest and most remote habitats, which are often believed to be protected from human influence,” AFP told AFP Mr. Pacoureau, also to Simon Fraser.

Significant decline in the number of sharks (AFP – John SAEKI)

The study points to overfishing and poor protection of these animals, calling for greater restrictions and better enforcement of existing rules.

Researchers note that species decline is not always irreversible if conservation efforts are undertaken.

The study focused on oceanic sharks and rays living primarily in the ocean, and found a clear trend: “Data reveals a yawning and growing hole in ocean life,” according to Pacoureau.

– Critical stage –

For 18 species for which they had more data, the researchers conclude that populations have fallen by more than 70% since 1970.

Dulvy believes that this figure was probably similar, if not worse, for other rays and oceanic sharks, but he could not say for lack of enough data.

These results even shocked experts, according to Mr. Pacoureau.

Three of their species are at a critical stage with a population having declined by more than 80%: the oceanic shark, the scalloped hammerhead shark and the great hammerhead shark.

Shark and ray populations are particularly at risk of collapse because these animals grow slowly and reproduce little.

According to the study, there has been a doubling in fifty years of the use of longlines and seine nets (a surface net) that capture marine life indiscriminately.

Regional bodies regulating international fishing companies “have not listed the protection of sharks and rays as a priority”, says Professor Pacoureau. By calling for a ban on the capture of endangered species and limits for those that are less.

“Protective measures can prevent a collapse of populations. And we know it works,” he said, using the example of the return of the great white shark to American waters after the application of protection rules.

According to Prof. Dulvy ordinary citizens can play a role in urging governments to respect their national and international commitments.

“Wherever you can, demand that your government watch out for sharks,” he said.

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