The Caribbean reef shark is endangered by fisheries
Andy Mann
Ray numbers are growing in coral reef ecosystems around the world as overfishing wipes out shark populations.
The findings come from a global study that used thousands of underwater cameras to examine the prevalence of sharks and rays on 391 coral reefs in 67 countries.
It found far fewer sharks than would be expected, with populations of species such as blacktip reef sharks, whitetip reef sharks, nurse sharks and gray reef sharks completely disappearing from the reefs in some places.
The populations of five of the most common reef shark species were 60 to 75 percent below their expected abundance, based on a modeled scenario with no human pressure, the study found.
Colin Simpfendorfer at James Cook University in Townsville, Australia, who led the research, says the decline was likely due to overfishing. In remote reefs, or in areas where reefs were within effective marine protected areas (MPAs), the sharks are much more numerous, he says — and this was more likely to be the case in higher-income countries.
![KEKM53 Bluespotted Ribbontail Ray, Taeniura lymma, Fury Shoal, Red Sea, Egypt](https://images.newscientist.com/wp-content/uploads/2023/06/15134657/SEI_160344634.jpg?width=1200)
The bluespotted ribbontail ray is abundant in the Indo-Pacific coral reefs
WaterFrame/Alamy
In many reefs where shark numbers have declined, rays have increased in numbers, the study found. The numbers of yellow and southern stingrays in the Atlantic, and blue-spotted maskrays and blue-spotted ribbontail rays in the Indo-Pacific, were higher where one or more species of reef sharks had been depleted. “We go from very shark-dominated communities to ray-dominated communities,” says Simpfendorfer.
These trends have a “cascading” effect throughout reef ecology, he says. For example, without sharks to hunt them, the number of herbivorous fish is skyrocketing. “They eat algae, and so we’ve seen coral reefs that lose reef sharks have a lot less carbon sequestered in the algae,” says Simpfendorfer.
As a result of the reef surveys, at least one species – the gray reef shark – has been reclassified as endangered by the International Union for Conservation of Nature.
Simpfendorfer says countries with coral reefs should get more support to enforce MPAs. “One of the things that comes out very clearly is that MPAs that are properly maintained are able to restore reef shark populations quite quickly,” he says.
Subjects: