A large number of affected animals were puppies and juveniles, which were mainly entangled around the neck by fishing lines.
Fishing lines and nets have a major impact on Cape fur seals (Arctocephalus pusillus pusillus), the most common marine mammal observed around the coasts of South Africa and Namibia, where they are endemic.
While their population is considered healthy, plastic pollution, and especially fishing lines and nets, causes horrific injuries and can lead to slow and painful deaths.
These are the first results of an ongoing project, launched in 2018, to study the impact of pollution on Cape fur seals in Namibia. The project involves researchers and environmentalists from the University of Stellenbosch, the Sea Search-Namibian Dolphin Project and Ocean Conservation Namibia.
The team is monitoring seal entanglement rates and Ocean Conservation Namibia has unraveled many affected animals. The first results of the project were published this week in the scientific journal Marine Pollution Bulletin.
Volunteers from the non-profit organization Ocean Conservation Namibia chasing young Cape fur seals to untangle those affected from fishing line injuries around their necks. Credit: Ocean Conservation Namibia
The study found that a large number of affected animals were puppies and juveniles, which were mainly entangled around the neck by fishing lines. The entanglement rates were approximately 1 per 500 animals and were similar between the two colonies studied at Walvis Bay and Cape Cross. Of the 347 documented entangled animals, the untangling team, led by NaudÃ© Dreyer of Ocean Conservation Namibia, successfully untangled 191 individuals between 2018 and March 2020.
Working in Africa with limited recourse, the team also compared low-cost data collection methods. They found that colony photographic scans were a fast and accurate method of collecting data on entangled individuals and the materials in which they were trapped.
Dr Tess Gridley, Co-Director of the Namibia Dolphin Project and Extraordinary Lecturer in the Department of Botany and Zoology at Stellenbosch University, says plastic pollution and especially lost and discarded fishing nets have a significant impact on the marine life: âOnce entangled, these seals face a very painful and uncertain future: finding food becomes more difficult and the wounds can become deep and debilitating, possibly causing death in many cases. Policy changes could help, such as financial incentives to recover lines, safe disposal of mosquito nets, and sustainable alternatives to plastics. “
Stephanie Curtis, Namibian Dolphin Project research student and lead author, says the impact of plastic pollution in the oceans is devastating: âSeals shouldn’t have to suffer this way because of our neglect with litter.
According to Dr Simon Elwen, co-director of the Namibian Dolphin Project and also associated with the League’s Department of Botany and Zoology, fur seals are particularly vulnerable to entanglement: âThey are very curious and playful animals and they will investigate objects in the water, but their thick, rear-facing fur that keeps them warm at sea easily snags lines and straps and prevents it from falling.
NaudÃ© Dreyer of Ocean Conservation Namibia says the project is underway: âAs of the start of 2021, we have already unraveled over 600 fur seals in just two colonies. This is the tip of the iceberg. It is imperative that studies like this highlight the consequences of plastic litter on marine animals and bring about change for the better. “
Reference: ‘Cape Fur Seal Entanglement (Arctocephalus pusillus pusillus) to the colonies of central Namibia âby S. Curtis, SH Elwen, N. Dreyer and T. Gridley, 4 August 2021, Marine Pollution Bulletin.
DOI: 10.1016 / j.marpolbul.2021.112759