Conservation / Ocean Plastics

Scientists gather data on shark and ray entanglements

written by Oceanographic Staff

University of Exeter scientists have so far discovered more than 1,000 reports of individuals caught in marine debris.

The team has noted that the true number is likely to be far higher, as few studies have focussed on plastic entanglement among shark and rays. They have been working with The Shark Trust to create a public online reporting tool for entanglement sightings called the Shark and Ray Entanglement Network (Sh.a.R.E.N) in order to gather more much needed research.

The most recent paper published alongside this study, Global review of shark and ray entanglement in anthropogenic marine debris, outlines that while entanglement in marine debris and ‘ghost nets’ doesn’t pose as high a threat as commercial fishing to rays and sharks, it still causes a great deal of unnecessary suffering to a huge number of animals.

The team of scientists found reports of 1,116 rays and sharks caught up in plastic in the world’s oceans after scouring existing studies and social media.

sharks-and-rays-entanglements-in-plastic-marine-debris-exeter-univeristy

“Due to the threats of direct over-fishing of sharks and rays, and ‘bycatch’ (accidental catching while fishing for other species), the issue of entanglement has perhaps gone a little under the radar,” said Co-author Professor Brendan Godley. “We set out to remedy this. Our study was the first to use Twitter to gather such data, and our results from the social media site revealed entanglements of species – and in places – not recorded in the academic papers.”

The scientists’ review of numerous academic papers found 557 cases of sharks and rays entangled in plastic. This included a range of 34 species across the Atlantic, Pacific and Indian oceans. Approximately 60% of these animals were either lesser spotted dogfish, spotted ratfish or spiny dogfish.

The researchers found 74 entanglement cases involving 559 individual sharks and rays from 26 species including tiger, whale, great white, and basking sharks reported by individuals on Twitter.

“One example in the study is a shortfin mako shark with fishing rope wrapped tightly around it,” said Kristian Parton, of the Centre for Ecology and Conservation on Exeter’s Penryn Campus in Cornwall. “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.”

Both data sources found that lost or discarded fishing gear appeared to be the most common objects causing entanglements. Other items included strapping bands used in packaging, polythene bags and rubber tyres.

“Although we don’t think entanglement is a major threat to the future of sharks and rays, it’s important to understand the range of threats facing these species, which are among the most threatened in the oceans,” added Parton. “Additionally, there’s a real animal welfare issue because entanglements can cause pain, suffering and even death.”

Photograph by Daniel Cartamil.

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