Alongside my work as a shark biologist, I am a volunteer for the charity Surfers Against Sewage. As part of this role I organise and participate in numerous beach cleans along the U.K. coastline, more often than not the bulk of rubbish that we remove during these cleans are plastic items. Now assuming you haven’t been marooned in outer space in recent years, you will be well aware of the mounting plastic crisis and the fact that particles of plastic can be found in just about everything, from the air we breathe to the water and food we consume.

The ingestion of plastic debris by marine animals has been documented across a variety of species

including; marine mammals, sea birds, sea turtles and some fish species. However fewer reports have described ingestion by sharks, and so for me it was a logical step to investigate whether a small shark species, commonly landed in the U.K. contained plastics. The small spotted catshark, more often referred to as the lesser spotted dogfish (cats… dogs… for the record they are catsharks, dogfish refer to another type of shark species), are often caught in bottom trawls and line gear, although technically bycatch the larger individuals are retained for human consumption, whilst the smaller ones are used for fish meal or pot bait.

I contacted a local fish merchant based in Fraserburgh on the Moray Firth Scotland, they kindly donated 20 sharks that had been captured in the North Sea and I set about investigating the contents of their gastrointestinal tracts, a polite way of saying I dug about and scrutinised their guts, recording any identifiable objects both natural and artificial.

Of the 20 sharks i sampled, all showed evidence of predation on natural prey sources prior to being trawl captured. Remains of hermit crab carapaces, squid beaks and fish bones were found. In addition to this 3 individuals were also found to contain plastic debris within their stomachs, one is a microplastic (defined as any particle less than 5mm) believed to be a micro-bead, the other two are macroplastics (>20mm); one is thought to be a broken and eroded tag and the other is composed of three fibres most likely originating as synthetic rope.

S. canicula are known to be opportunistic feeders that predate on a wide range of fauna, including shellfish, crabs, squid and small fish. It is unclear as to whether the plastics found within the stomachs of S. canicula had been ingested directly from the water column itself, or whether these items had been previously consumed by their prey. It remains unknown for now as to whether the ingestion of these plastics will negatively impact the individual sharks, however recent studies show that the potential effects on marine species from the uptake of microplastics include; reduced survival, inability to predate effectively, oxidative status and uptake of persistent organic pollutants. Current research is now investigating the effects of biomagnification and bioaccumulation of plastics and associated chemicals throughout freshwater and marine ecosystems.

S. canicula are considered an abundant shark species with an IUCN (International Union for the Conservation Nature) Red List status of “least concern”and yet with increasing environmental threats such as plastic ingestion, combined with the overfishing of other species, resulting in these sharks being used as market substitutes, it remains to be seen for how long this status will hold true.

My study reports the first evidence of plastic debris in the stomach of S. canicula, and yet I wasn’t surprised, heck I expected to find some evidence of plastics I just wasn’t sure how much. If this isn’t depressing and a sign of our times I don’t know what is. But with recent reports detailing that an estimated 75% of all the litter in our oceans is plastic, and with around 5 million tonnes of plastic waste entering the seas annually (Thompson, 2017), its no wonder I am not surprised only saddened that I am finding plastic in the guts of sharks.

What’s the link between beach cleans and shark guts?

Alongside my work as a shark biologist, I am a volunteer for the charity Surfers Against Sewage. As part of this role I organise and participate in numerous beach cleans along the U.K. coastline, more often than not the bulk of rubbish that we remove during these cleans are plastic items. Now assuming you haven’t been marooned in outer space in recent years, you will be well aware of the mounting plastic crisis and the fact that particles of plastic can be found in just about everything, from the air we breathe to the water and food we consume.

The ingestion of plastic debris by marine animals has been documented across a variety of species

including; marine mammals, sea birds, sea turtles and some fish species. However fewer reports have described ingestion by sharks, and so for me it was a logical step to investigate whether a small shark species, commonly landed in the U.K. contained plastics. The small spotted catshark, more often referred to as the lesser spotted dogfish (cats… dogs… for the record they are catsharks, dogfish refer to another type of shark species), are often caught in bottom trawls and line gear, although technically bycatch the larger individuals are retained for human consumption, whilst the smaller ones are used for fish meal or pot bait.

I contacted a local fish merchant based in Fraserburgh on the Moray Firth Scotland, they kindly donated 20 sharks that had been captured in the North Sea and I set about investigating the contents of their gastrointestinal tracts, a polite way of saying I dug about and scrutinised their guts, recording any identifiable objects both natural and artificial.

Of the 20 sharks i sampled, all showed evidence of predation on natural prey sources

prior to being trawl captured. Remains of hermit crab carapaces, squid beaks and fish bones were found. In addition to this 3 individuals were also found to contain plastic debris within their stomachs, one is a microplastic (defined as any particle less than 5mm) believed to be a micro-bead, the other two are macroplastics (>20mm); one is thought to be a broken and eroded tag and the other is composed of three fibres most likely originating as synthetic rope.

S. canicula are known to be opportunistic feeders that predate on a wide range of fauna, including shellfish, crabs, squid and small fish. It is unclear as to whether the plastics found within the stomachs of S. canicula had been ingested directly from the water column itself, or whether these items had been previously consumed by their prey. It remains unknown for now as to whether the ingestion of these plastics will negatively impact the individual sharks, however recent studies show that the potential effects on marine species from the uptake of microplastics include; reduced survival, inability to predate effectively, oxidative status and uptake of persistent organic pollutants. Current research is now investigating the effects of biomagnification and bioaccumulation of plastics and associated chemicals throughout freshwater and marine ecosystems.

S. canicula are considered an abundant shark species with an IUCN (International Union for the Conservation Nature) Red List status of “least concern”and yet with increasing environmental threats such as plastic ingestion, combined with the overfishing of other species, resulting in these sharks being used as market substitutes, it remains to be seen for how long this status will hold true.

My study reports the first evidence of plastic debris in the stomach of S. canicula, and yet I wasn’t surprised, heck I expected to find some evidence of plastics I just wasn’t sure how much. If this isn’t depressing and a sign of our times I don’t know what is. But with recent reports detailing that an estimated 75% of all the litter in our oceans is plastic, and with around 5 million tonnes of plastic waste entering the seas annually (Thompson, 2017), its no wonder I am not surprised only saddened that I am finding plastic in the guts of sharks.

Having visited 25 beaches in the past 6 months, along the U.K., French, Spanish & Portuguese coastlines and having found plastics on every single one of those beaches the consequences of our plastic mania will be felt far into the future. However the current wave of awareness about plastic pollution amongst the general public is encouraging, the more information and education that is provided via environmental charities such as Surfers Against Sewage and through TV Shows like Blue Planet 2 as well as on social media, will create positive change by allowing people not only to make more informed choices but also to lobby and campaign to bring about change, that is so desperately required.

References

Avio, C.J., Gorbi, S., Regoli, F., 2017. Plastics and microplastics in the oceans: From emerging

pollutants to emerged threats. Marine environmental research. 1-10.

Colmenero, A.I., Barria, C., Broglio, E., Garcia-Barcelona, S., 2017. Plastic debris straps on threatened blue shark Prionace glauca. Marine Pollution Bulletin. 115, 436-438.

Derraik, J.G.B., 2002. The pollution of the marine environment by plastic debris: a review. Marine

Pollution Bulletin. 44 (9), 842-852.

Mallory, M.L., 2008. Marine plastic debris in northern fulmars from the Canadian high Arctic. Marine Pollution Bulletin. 56, 1501-1504.

Putnam, A.R., Clune, A., Buksa, B., Hammer, C., VanBrockin, H., 2017. Microplastic biomagnification in Invertebrates, Fish and Cormorants in Lake Champlain. Centre for Earth and Environmental

Science. 37.

Smith, L.E., 2018. Plastic ingestion by Scyliorhinus canicula trawl captured in the North Sea. Marine Pollution Bulletin. 130. 6-7.

Thompson, R., 2017. A journey on plastic seas. Nature. 547, 278-279.