North East Atlantic Sharks Contaminated With Microplastic and Fibres
Forty-six specimens containing a mixture of four species of demersal (living near the sea bed) shark were, collected as the result of bycatch by local fisheries, were examined. A sizeable majority contained at least one particle of microplastic or microplastic fibre, with one specimen containing 154 fibres of a blue plastic rope.
While the study acknowledges the 'modest' sample size, it also reports that the percentage of contaminated fish was consistent across the four different species analysed: 66.6% of small-spotted catsharks (Scyliorhinus canicula), 75% of starry smooth-hound (Mustelus asterias), 58% of spiny dogfish (Squalus acanthias) and 70% of the bull huss (Scyliorhinus stellaris) that formed the sample group were found to be contaminated.
The consistency between samples indicates that the level of microplastic contamination could reflect the demersal shark population in UK waters as a whole, and is perhaps, even on the low side.
In an e-mail to DIVE, Kristian Parsons, lead author of the study, said: 'I feel like [the levels of contaminants in the sampled sharks] could most definitely be extrapolated to demersal shark populations across the UK. It would be interesting to see whether sharks that live in perhaps slightly more polluted areas of the UK contain more ingested contaminants.
'I’d particularly be interested to see what these levels were for sharks inhabiting the English Channel and around the more populated English coastal cities. The North-East Atlantic (and Cornish waters) are thought to be relatively less-polluted so to find these fibres and other contaminants was surprising, but also interesting, and tells us more about the pervasive nature of this pollution.'
Microplastics exist in all regions of the ocean, from shallow coastal areas to the 11,000m depths of the Mariana Trench. The amount of research is growing, and the presence of microplastics has been identified in many small shellfish and crustaceans, bony fish and huge filter feeders such as whale sharks and manta rays, but there has been little research into the presence of microplastics in the general shark population.
The sharks are thought to have ingested the microplastics through consuming smaller creatures which are already known to have microplastics embedded in their flesh, or as a result of the sharks' method of feeding. All four species tend to suck their prey from the sea bed, where particles of sand and other inorganic material may be ingested as a result. Previous studies have already found that the sediment on the seafloor is contaminated by a range of man-made products, including plastic microbeads, which were banned in the UK for use in cosmetic products in 2018.
Whether or not the ingested plastic and fibres caused any damage to the shark, either physically or chemically, is not established by the study. Its presence, however, has implications not just for the sharks, but also for the human food chain.
'We may be unknowingly consuming these shark species across the country in fish and chip shops,' said Parsons. 'Often these shark species are sold under pseudonyms such as “rock salmon” or “rock eel”. If it is shown that these contaminants are in the flesh of these shark species, then we as humans may be consuming them. However, it is still important to note that as of currently we don’t know the impacts of plastic ingestion on humans. It should also be noted that there are several other seafood products that will be transferring more plastics to humans, for example, the extremely popular shellfish industry.'
The study is yet another indication as to the ubiquity of microplastics and plastic pollution, and the threat they pose to both the marine environment and the human population. Entanglement with abandoned, lost and discarded fishing equipment (ghost gear) is a serious danger for larger animals, and plastic bags can be mistaken as jellyfish, a food source for a number of different species. Microplastics, however, pose a hazard on a scale that is yet to be fully understood.
'If the plastic problem is left unchecked the consequences for the marine realm could be deadly,' said Parsons. 'Regarding the smaller, more obscure microplastics, the internal impacts on wildlife can be severe, with damage to stomach linings, problems associated with false satiation (feeling full when they’re not), and then a whole host of changes to internal body systems, including growth suppression, lowering of immune systems, changes in their reproductive systems.
'The potential for damage is extensive,' he added, 'so it is a problem we really need to address very soon.'
The complete study by Parton, K.J., Godley, B.J., Santillo, D. et al., 'Investigating the presence of microplastics in demersal sharks of the North-East Atlantic', Sci Rep 10, 12204 (2020) is published in the online journal Scientific Reports at https://doi.org/10.1038/s41598-020-68680-1