Sharks and rays under threat from plastic pollution, study says

sharks and rays plastic entanglement
© iStock/Alessandro De Maddalena

A new study has found hundreds of sharks and rays have become entangled in plastic waste, most of it discarded fishing equipment.

The University of Exeter’s paper ‘A global review of shark and ray entanglement in anthropogenic marine debris’, published in the Endangered Species Research journal, is the first to focus specifically on sharks and rays. Researchers conducted a wide-ranging review spanning previously published studies and entanglement reports on Twitter; and found more than 1,000 reports of sharks and rays caught in discarded plastic.

Kristian Parton, of the University of Exeter’s Centre for Ecology and Conservation, said: “One example in the study is a shortfin mako shark with fishing rope wrapped tightly around it. 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. 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. Additionally, there’s a real animal welfare issue because entanglements can cause pain, suffering and even death.”

The study highlighted a number of risk factors which appeared to affect the safety of certain species of sharks and rays:

  • Body shape – sharks appeared to be more at risk of entanglement than rays, while unusually shaped species such as sawfish and manta rays also displayed higher levels of risk;
  • Habitat – plastic entanglement particularly affected species living on the sea floor, where discarded plastic sinks; and in the open ocean; and
  • Migration habits – the greater the distance travelled by a species, the higher its risk of becoming entangled.

Co-author Professor Brendan Godley, co-ordinator of the university’s marine strategy, said: “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. 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 researchers state further data is needed to build a coherent picture of the risk posed by plastic entanglement to sharks and rays; and have established an online reporting form in partnership with the Shark Trust.

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