Sharks and rays get tangled in plastic

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Sharks and rays get tangled in plastic

July 07, 2019 - 22:06
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Plastic is now being found in all sections of the water column, from the epipelagic zone at the surface to thedeep sea trenches of the hadopelagic zone, in all ofthe world’s oceans.

An adult shortfin mako shark entangled in fishing rope (biofouled with barnacles) in the Pacific Ocean, causing scoliosis of the back.

University of Exeter scientists scoured existing published studies and Twitter for shark and ray entanglements, and found reports of more than 1,000 entangled individuals.

And they say the true number is likely to be far higher, as few studies have focussed on plastic entanglement among shark and rays.

Sharks and rays generally display life history traits such as late maturation, low reproductive output and long life span, making them highly susceptible to a variety of anthropogenic threats.

Elasmobranchs are suggested to be less vulnerable to plastic pollution than other large marine species; however, this could be a consequence of a lack of studies rather than an inherently lower susceptibility. Entanglement can lead to starvation, suffocation, immobilisation and ultimately death

Entanglement of elasmobranchs in marine debris is relatively understudied within the scientific literature, with only a handful of studies investigating the problems elasmobranchs face regarding entanglement in plastic pollution. Of the studies which have been conducted on the topic of plastic ingestion, several have highlighted that large filter-feeding elasmobranchs may be particularly vulnerable to this threat. Only a few studies have touched on the categories of anthropogenic debris that may entangle elasmobranchs the most, with a particular focus on ghost fishing gear.

Ghost fishing gear

The researchers found that ghost fishing gear was responsible for over two-thirds of all the entanglement records in the published literature for sharks and rays. Alongside this, 60% of total entangled animals had their entire body trapped animals), as more often than not when animals are entangled in ghost fishing gear, they become twisted in the material, trapping their entire bodies in the process.

The scientists found entanglement of sharks and rays is likely underreported in the scientific literature and identify it as a clear animal welfare issue.

Shark finning is still a worse threat

The numbers of entangled elasmobranchs reported here are minimal in comparison to the numbers of elasmobranchs caught directly in targeted fisheries or indirectly as bycatch. Nonetheless, there is no doubt that entanglement in anthropogenic debris is an additional threat to sharks and rays.

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