Plastic pollution causes horrific injuries to Cape fur seals in two Namibian colonies

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Entanglement in plastic pollution, mainly discarded fishing lines and nets, is causing horrific injuries to hundreds of Cape fur seals every year.

These are the first results from an ongoing project, which started in 2018, to investigate the effects of pollution on Cape fur seals in Namibia. The seals are the most common marine mammal observed around the coastline of South Africa and Namibia, where they are endemic.

The research was led by a team of researchers and conservationists from Stellenbosch University, the Sea Search-Namibian Dolphin Project and Ocean Conservation Namibia.

The findings, published in the scientific journal Marine Pollution Bulletin, show that rates of entanglement were about one per 500 animals and similar between the two colonies investigated at Walvis Bay and Cape Cross. 

Of the 347 entangled animals documented, the disentanglement team, led by Naudé Dreyer of Ocean Conservation Namibia, were able to successfully disentangle 191 individuals between 2018 and March 2020.

The results, says the team, “support the global view that the primary cause of entanglement in seals, particularly fur seals, is fishing material”. 

Pups and juveniles were most commonly affected, by being entangled around the neck by fishing line. Within the life cycle of Cape fur seals, there are periods in which interaction with marine waste is likely to be higher.

“Juveniles in this study exhibited the highest number of entanglements. This may be attributed to a more curious nature in younger seals, whereby they likely ‘play’ with waste material like they would with kelp,” according to the research. 

Immature seals, which do not yet have the dive capabilities of adults, are more likely to interact with waste close to their colony as they explore and develop their foraging skills, but they can also fit into material made of finer mesh because of their size.

It is clear, according to the paper, that the overlap between human habitation and either intense fishing activity or the accrual of marine debris through ocean currents “results in areas with high rates of entanglements”. 

Although the rate of entanglement observed at the colonies does not appear to be negatively affecting the global population size, which has remained relatively stable since the early 1990s, entanglement has a clear effect on individual animal welfare. 

“Most entanglements identified … were classified as ‘slight’ injuries, with no visible skin wounds. These milder injuries have the potential to progress into more severe injuries, especially as the animals grow, and should thus remain targets of disentanglement efforts,” the paper says. 

The relatively small number of “very severe” cases is likely because seals exhibiting these injuries are at a higher risk of mortality and may not be observed because of increased time at sea or “dying unseen”.

For now, entanglement material can only be identified to broad industry and not specific companies, but the information in the paper “provides a useful starting point to engage with the key industries to decrease pollution in the bay”, according to the authors.