Photo by Daniel Cartamil
As previously reported by WAN, plastic waste in our world’s oceans has become an epidemic that is leaving innocent marine animals entangled, injured, or worse, killed in their ocean homes.
According to a new study by University of Exeter in the UK, researchers scoured existing published studies and Twitter for shark and ray entanglements, and found reports of more than 1,000 entangled individuals; a number that is likely to be far higher, “as few studies have focused on plastic entanglement among shark and rays.”
As per the study, such entanglement, mostly involving lost or discarded fishing gear, is a “far lesser threat” to sharks and rays than commercial fishing; but the suffering it causes is a serious animal welfare concern.
“One example in the study is a shortfin mako shark with fishing rope wrapped tightly around it,” Kristian Parton, of the Centre for Ecology and Conservation on Exeter’s Penryn Campus in Cornwall, said 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.”
Parton noted that it is important for people to understand the range of threats facing these species which are among the most threatened in our oceans.
“Due to the threats of direct over-fishing of sharks and rays, and ‘bycatch’ which is the accidental catching while fishing for other species, the issue of entanglement has perhaps gone a little under the radar,” stated co-author Professor Brendan Godley, coordinator of the university’s marine strategy, who explained that the study was launched 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, that are not recorded in the academic papers.”
The review of academic papers found reports of 557 sharks and rays entangled in plastic, spanning 34 species in oceans including the Atlantic, Pacific and Indian. Almost 60% of these animals 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 data sources suggested “ghost” fishing gear, including nets, lines and other equipment that may have been lost or abandoned, were by far the most common entangling objects. Other items included strapping bands used in packaging, polythene bags and rubber tires.
The study identified factors that appear to put certain species more at risk:
Habitat – sharks and rays in the open ocean appear more likely to get entangled, as do those living on the sea floor, where materials such as nets loaded with dead fish sink and attract predators, which in turn get stuck.
Migration – species that cover long distances appear more at risk of encountering plastic waste.
Body shape – sharks seem to be at greater risk than rays. Species with unusual features, such as manta rays, basking sharks and sawfish, are also at greater risk.