Research quantifies plastic risk to sharks and rays

Discarded fishing gear is the major culprit. Nick Carne reports.

An adult shortfin mako shark (Isurus oxyrinchus) caught in a fishing rope covered with barnacles in the Pacific Ocean.

Daniel Cartamil

Sharks and rays are becoming entangled in plastic waste in oceans across the world to a worrying extent – and social media helps us know that.

Researchers from the University of Exeter, UK, scoured Twitter, as well as existing published studies, and found reports of more than a thousand individual entanglements. They suspect the actual number is far higher.

Most involved lost or discarded fishing gear.

While such entanglements don’t pose a major threat to the future of sharks and rays, the researchers say, they do flag serious animal welfare issues.

"One example in the study is a shortfin mako shark with fishing rope wrapped tightly around it," says co-author Kristian Parton.

"The shark had clearly continued growing after becoming entangled, so the rope – which was covered in barnacles – had dug into its skin and damaged its spine.”

Colleague Brendan Godley says the issue of entanglement has perhaps gone under the radar due to a focus on direct over-fishing and “bycatch” – sharks and rays being accidentally caught with other species.

The review of academic papers found 557 reports of entanglements, spanning 34 species in the Atlantic, Pacific and Indian oceans. Almost 60% were either lesser spotted dogfish, spotted ratfish or spiny dogfish.

On Twitter, the researchers found 74 entanglement reports involving 559 individual sharks and rays from 26 species, including whale sharks, great whites, tiger sharks and basking sharks.

Both sources suggested "ghost" fishing gear (nets, lines and other equipment lost or abandoned) were by far the most common entangling objects. Other items included strapping bands used in packaging, polythene bags and rubber tyres.

Body shape appears to be a factor, the researchers say. In general, sharks are at greater risk than rays, and species with unusual features, such as manta rays and basking sharks, also are more likely to become entangled.

The findings are published in the journal Endangered Species Research.

The UK-based Shark Trust has created an online report form to gather reports of entanglements from anywhere in the world.

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