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Monitoring the growing risk of extinction of sharks and rays


Our natural environment is declining globally at a rate unprecedented in our human history – with the increasing number of species extinctions, we are almost certain to see serious impacts not only on the health of ecosystems, but also on our quality of life (economies, livelihoods, food security and health).

A 2019 United Nations report showed that three quarters of the terrestrial environment and around 66% of the marine environment have been significantly changed by our actions. (On average, these trends have been less severe or avoided in areas owned or managed by Indigenous Peoples and local communities.) And while this biodiversity loss is increasingly observed and well understood on land, the trajectories of risk of extinction remain largely unknown in the ocean. . “I personally think it’s important that we try to understand the effects we are having on marine biodiversity before it’s too late to reverse them, because I naturally care about biodiversity loss, as a conservation biologist,” said Dr. Rachel HL Walls. “But another way of looking at it is that the oceans, if managed sustainably, could be an inexhaustible source of protein for us. In the face of food insecurity, it is in our interest to determine the extent of the decline caused by overfishing now before it is too late to reverse, so that we can more accurately calculate how to manage marine resources sustainably so that they can continue to sustain us for many years to come.

The International Union for Conservation of Nature (IUCN) Red List is a key indicator of the health of global biodiversity, with experts assessing the conservation status of species globally. Most species (including marine) that move between IUCN Red List Categories do so due to improved knowledge or revised taxonomy. This therefore means that it is impossible to determine meaningful trends in the “state” of biodiversity by simply looking at the number of threatened species between updates. This is why the Red List Index (RLI) was developed – it shows trends in the status of groups of species based only on genuine improvements or deteriorations in status of sufficient magnitude to qualify species for inclusion in the Red List categories of more or less threatened. .

The RLI shows trends in the overall risk of species extinction and is used by governments to track their progress towards targets for reducing biodiversity loss. But it’s not perfect. The IUCN Red List divides species into nine categories: Not Assessed, Data Deficient, Least Concern, Near Threatened, Vulnerable, Endangered, Critically Endangered, Extinct in the Wild, and Extinct. The RLI only includes species listed in six of these categories (Least Concern, Near Treated, Vulnerable, Endangered, Critically Endangered and Extinct). Specifically, the RLI excludes the Data Deficient category, into which species are placed if there is insufficient information to assess their risk of extinction based on distribution and/or population status.

While the RLI has primarily been applied to terrestrial species, including birds, mammals, and amphibians, it can also be used for marine ecosystems. “Our only understanding of the evolution of the RLI’s marine extinction risk so far comes from its application to hard corals, which reveals the threat of climate change to a key group of fundamental species in the tropical oceans,” they wrote. said scientists Dr. Rachel HL Walls and Dr. Nicholas K. Dulvy State in their new study. Using RLIs, scientists tracked the extinction risk of 119 Northeast Atlantic Chondrichthyan species and 72 Mediterranean species (sharks, rays and chimaeras) primarily threatened by our unsustainable fishing habits. “Their slower life cycles and consequently greater susceptibility to overfishing might consider them a ‘canary in the coal mine’ for other exploited marine species in general, when considering the effects of overfishing: a early warning of what could happen if we don’t slow things down,” Walls explained. “Europe has proven to be an extremely interesting case study because of the mismatch in fisheries management between the Northeast Atlantic and the Mediterranean Sea.

Chondrichthyes have the largest percentage of “threatened” (i.e. vulnerable, endangered, or critically endangered) species of any taxonomic class of marine organisms, with numerous populations in the world already locally or regionally extinct due to overfishing. However, these percentages do not include all globally data deficient species (which currently lack sufficient information on population size, trends, distribution and/or threats to assess them against the criteria for the Red List).

It should come as no surprise that sustainable harvesting underpins food security and human well-being. Yet Walls and Dulvy found profound and long-recognized differences between the management of Northeast Atlantic and Mediterranean fisheries and there have been few effectively implemented solutions to benefit sharks and rays. in this region, causing them to face high levels of extinction risk by 1980…and since then their condition has steadily worsened. The RLI is scaled from zero to one, where zero means all species are extinct and one means all species are of least concern. In the northeast Atlantic, researchers found that the RLI of sharks and rays fell from a retrospective value of 0.80 in 1980 to 0.74 in 2005 and then to 0.72 in 2015 (a drop of 8% of RLI).

“For me, the hardest part of this research was realizing how high the risk of extinction for sharks and rays is in the Mediterranean Sea,” Walls said. “We knew in the early 2000s that shark and ray populations were declining across Europe, but the lack of management action taken to improve things in the Mediterranean Sea has led to the complete disappearance of species from the basin. due to overfishing, and many other declines”.

“I like to think that our research [will] inform stricter management for sharks and rays. That’s why we chose to publish in an open access journal, so everyone can see what we found and hopefully someone chooses to do something about it,” Walls said, who went on to say that she wanted bycatch reporting to be mandatory. “The absolute ideal would be for fisheries managers to recalculate their definitions of ‘sustainable fishing’ to incorporate the slower life histories of sharks and rays, so that fishing effort is reduced to allow for the renewal of the population of longer-lived bycatch species.” Walls also explained how when fisheries managers calculate their maximum sustainable yields, or equivalent, they do not consider bycatch species, and no record of their bycatch is applied.

As for data-deficient species, Walls and Dulvy believe that they should be treated with caution in terms of protection and environmental impact assessment, and considered urgent priorities for investigation and research to elucidate their real status. Although many of these changes relate to the fishing industry, the public can do a lot to help! “I think the best thing [to do is] manage [your] own consumption of marine resources. For example, a lot of information is now available on the sustainability of different types of fishing. Even if the tuna steak you buy says it was fished sustainably, that label only refers to that species, it doesn’t mean the fishery is sustainable for sharks, rays, turtles sea, etc If the demand for unsustainably caught seafood declines, then perhaps the incentive to overfish will be reduced,” Walls commented.