“Catastrophic” decline in shark and ray populations over the past fifty years

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Populations of sharks and ocean rays have declined by 70% over the past fifty years, according to a new study published in Nature. At issue: overfishing.

We know that overfishing is the main cause of the disappearance of marine species. However, the decrease and increase in the risk of extinction of individual species is still difficult to measure today, especially for large predators in the high seas.

In a recent study, researchers at Simon Fraser University (SFU) used two indicators to track progress made in recent years in marine biodiversity under the “Goals of”. Aichi ”. As a reminder, this is the “Strategic Plan for Biodiversity 2011-2020” for the planet adopted in 2010.

The first dataset used was the “Living Planet Index”, a measure of changes in abundance aggregated from 57 datasets for 18 species of sharks and ocean rays. The second was the Red List Index, a measure of the change in extinction risk calculated for the 31 oceanic species of sharks and rays.

-70% in 50 years

The results, of course, are not good. Analysis of these data has indeed revealed that the global abundance of sharks and ocean rays has decreased by 71% since 1970. Many species are affected, from hammerhead sharks to manta rays.

The most striking example is that of the longiman shark, also called oceanic shark. Targeted for their fins, these fish have seen their global population fall by 98% in the last sixty years. “This is a decline worse than that of most of the large populations of land mammals”, underlines to AFP Nick Dulvy, principal author of the study.

As a reminder, sharks and rays are particularly vulnerable to the collapse of the population, insofar as their reproduction rate is relatively low, and that they slowly develop.

Credit: Eychenne / Pixabay

The problem of overfishing

The reasons for these mass disappearances? An 18-fold increase in the relative fishing pressure, the authors point out. The study also notes a doubling over the past half-century in the use of longline and purse seine fisheries. The main disadvantage of these methods is that they trap bycatch in addition to the species normally targeted.

Still according to the researchers, the species affected by these declines could make a comeback, if and only if conservation efforts are made. Strict bans and precautionary science-based catch limits are urgently needed to help species recover.

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