Whale entanglements in South African trap fisheries and their potential mitigation through ropeless fishing techniques

• Main Author: Daniel, Michael Talbot
• Other Authors: Attwood, Colin
• Format: Master Thesis
• Language: English
• Published: Faculty of Science 2022
• Subjects: Ocean Sciences; Humpback Whale; Megaptera novaeangliae; Southern Right Whale
• Online Access: http://hdl.handle.net/11427/37055; https://open.uct.ac.za/bitstream/11427/37055/1/thesis_sci_2022_daniel%20michael%20talbot.pdf

The increasing frequency of whale entanglements in fishing gear is a global concern. In South African waters, the west coast rock lobster (WCRL), south coast rock lobster (SCRL) and octopus fisheries are responsible for whale entanglements in trap fishing gear. To better understand the interactions between whale species and fishing gear, a study was conducted in which whale entanglement and fishing effort data were analysed. Annual whale entanglements increased since 2006, despite an overall decrease in trap fishing effort. Entanglement hotspots corresponded with fishing hotspots. The WCRL fishery was responsible for 68% of all entanglements between 2006 and 2020. Of particular concern was zone D of the WCRL fishing area, where 90% of whale entanglements in the fishery occurred; the same area where 92% of fishing effort took place. Entanglements in SCRL fishing hotspot, near the remote southern tip of the Agulhas Bank, are likely to be underreported. Humpback (Megaptera novaeangliae), southern right (Eubalaena australis) and Bryde's (Balaenoptera brydei) whales accounted for 64%, 25%, and 11% of entanglements, respectively. Species and area specific GLMs showed that humpback whale entanglements increased over the whole South African coastline and in all trap fisheries. This increase was attributed to the aggregation of humpback whales in ‘super-groups' off the west coast during summer months over the past decade. Consequently, a primary seasonal peak in entanglements occurred between January and March. Southern right whale entanglements decreased since 2006 over the whole South African coastline and in the WCRL fishery. This decrease was attributed to a northern shift in foraging by this species over the past decade. Bryde's whale entanglements increased since 2006 across the South African coastline, and most strongly in the octopus fishery. Since all Bryde's entanglements occurred in the past six years, a change in distribution of the species is suspected. Bryde's whale entanglements are of high concern due to ...