Investigating interactions of South African longline fisheries with orcas and Cape fur seals

• Increase understanding of the risks to orcas (killer whales) and Cape fur seals during depredation
• Use existing fisheries observer data to quantify depredation rates over the past 20 years
• Inform management decisions around minimising marine mammal interactions and improving hake stock assessments

Improving fishing practices though data collection

The South African hake longline fishery is verified as part of the In-Transition to MSC Program and is aiming for certification to the MSC Fisheries Standard. As part of the assessment process the fishery must demonstrate it is minimising its impacts on Endangered, Threatened and Protected (ETP) species, habitats and the wider ecosystem. It must also ensure its target stocks are at sustainable levels, and it is harvesting within well-defined catch limits derived from accurate stock assessments.

Fishing for two species of hake: Deep-water Cape hake (Merluccius paradoxus) and shallow-water cape hake (Merluccius capensis), the vessels deploy longlines and baited hooks and, like most commercial fisheries of this type, its catch is subject to depredation by marine mammals.

Depredation is a frequent phenomenon that occurs when predators such as marine mammals, feed directly from fishing gear. For the South African longline fishery this can result in unintended interactions with orcas and Cape fur seals. It also makes it hard for fisheries to calculate whether they are fishing within sustainable catch limits, as large amounts of the catch are not landed. The depredated catch is considered “lost” and therefore stock assessments cannot fully measure abundance and results are incomplete.

Informed decisions to minimise interactions

To meet the MSC Standard the fishery is currently working with scientists at Stellenbosch University to improve its sustainability performance indicators. OSF Student Research Grant recipient, Lindiwe Makapela, is a master’s student from the university, whose research project will support the fishery.

By analysing existing scientific observers’ data from the last twenty years, the project will compare and contrast the depredation behaviours of the mammals, and the fishery’s operational methods to better understand how to mitigate and minimise interactions. Additionally, it will investigate and quantify true catch values, after depredation effects.

The research outputs will close data gaps and will inform management recommendations to change fishing methods that minimise the fishery’s impact on ETP species.