More Than a Third of Shark Species Are Now Threatened With Extinction

Overfishing, habitat loss and climate change are behind the ‘desperate’ decline

A hammerhead shark
Hammerhead sharks have are considered critically endangered. Christa Rohrbach via Flickr under CC BY-NC-SA 2.0

More than one-third of the world's shark and ray species are now facing the threat of extinction, the International Union for the Conservation of Nature (IUCN) has declared in the latest update to its Red List of Threatened Species.

The update was prompted by new research published in the journal Current Biology that analyzed nearly 1,200 species of Chondrichthyes, a taxonomic class of fish with skeletons made mainly of cartilage, reports the Guardian's Karen McVeigh. Of those chondrichthyes, 37 percent were considered to be "vulnerable," "endangered" or "critically endangered."

“The widespread depletion of these fishes, particularly sharks and rays, jeopardises the health of entire ocean ecosystems and food security for many nations around the globe,” says marine ecologist Nicholas Dulvy, lead author on the new study.

Chondrichthyes have lived on Earth for roughly 420 million years and survived at least five mass extinction events. Three species have not been spotted in nature in several decades and may already be extinct, with many other species imperiled.

The largest threat the IUCN report and Current Biology study identified to the sharks and rays is overfishing, reports the Guardian. Though they are not commonly sought out by fishers, these animals often end up as "bycatch" in nets meant to capture other species, according to the study. Instead of being released, the sharks caught this way are usually kept and used for food or feeding livestock.

"The alarm bells couldn't be ringing louder for sharks and rays," says Andy Cornish, a shark expert at the World Wildlife Fund, to Helen Briggs of the BBC. "We are losing this ancient group of creatures - starting to lose it species by species right here, right now - we desperately need urgent action."

What makes overfishing of sharks and rays so harmful is the fact that they have a relatively low reproduction rate compared to other fish species, per the Guardian. Sharks, for example, usually give birth to only a few young at a time, and these newborn sharks take years to reach the age where they can reproduce.

Tropical and subtropical sharks and rays are staring down the greatest threats to existence, according to the IUCN, because highly populated coastal areas and a large amount of unregulated fishing are putting extreme pressure on their populations.

“The tropics host incredible shark and ray diversity, but too many of these inherently vulnerable species have been heavily fished for more than a century by a wide range of fisheries that remain poorly managed, despite countless commitments to improve," says marine biologist Colin Simpendorfer of James Cook University in an IUCN statement.

Per the Current Biology study, other factors pressuring sharks and rays include pollution, habitat loss and climate change-driven warming ocean waters.

Komodo dragons are also facing increased threats, as the IUCN shifted their status from "vulnerable" to "endangered," reports Katy Evans of IFLScience. Earth's largest lizard lives on just two islands in Indonesia, and they could lose significant amounts of their habitat to rising ocean levels in the coming decades, a study published last year in the journal Ecology and Evolution found.

“The idea that these prehistoric animals have moved one step closer to extinction due in part to climate change is terrifying," says Andrew Terry, conservation director at the Zoological Society of London, in an IUCN statement.

Not all of the updates announced during the IUCN's World Conservation Congress in France were negative, however, the BBC reports. Four species of heavily harvested tuna fish saw their classifications upgraded on the IUCN's Red List following efforts in recent years to limit illegal fishing and implement catch quotas.