Over 1,000 sharks and rays have become entangled in oceanic plastic waste in what researchers say is a “clear animal welfare issue,” according to a systematic review published in the journal Endangered Species Research.
To review how susceptible cartilaginous fishes such as sharks, skates, and rays are to entanglement, researchers analyzed existing data and research and collected reports of entanglements posted to Twitter. They found records of more than 1,000 entangled individuals in their study – a number they say is likely to be higher given the fact that few studies have focused on plastic entanglement in sharks and rays.
“One example in the study is a shortfin mako shark with fishing rope wrapped tightly around it," said study author Kristian Parton in a statement. "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.”
Across 47 published events in more than two dozen scientific papers, researchers found that 16 different families encompassing 34 different species from three major ocean basins are impacted by human waste. In particular, nearly three-quarters of those instances involved “discarded, lost, or abandoned fishing gear in the marine environment,” known as ghost fishing gear.
Nets, traps, pots, and other “derelict fishing gear” inadvertently traps animals and smothers habitats. More than one in 10 occurrences involved polypropylene strapping bands, heavy-duty straps used to bind together pallets and other products. Other materials include circular plastic debris, grocery bags, and rubber tires. Throughout the studies, entanglements were most commonly recorded in the Pacific and Atlantic Oceans, 49 percent and 46 percent respectively. Turning to Twitter, researchers logged 74 cases of entanglement across 14 families and 26 species. Again, ghost fishing gear was the most commonly reported, affecting nearly 95 percent of cases documented.
Even so, entanglement is a “far lesser threat” to sharks and rays than fisheries, which harvest both these fish and the prey they rely on.
"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,” said Parton.
The authors note that their work is symptomatic of an overall degraded marine environment, citing a need for standardization of how to report such occurrences in order to quantify entanglement risks and find hotspots. In that vein, the researchers teamed up with Shark Trust Record to create an online form that allows people to self-report sightings to record more information on entanglements.