Evidence of deep-sea interactions between toothed whales and longlines

• Main Authors: G Richard, J Bonnel, P Tixier, John Arnould, A Janc, C Guinet
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2020
• Subjects: Science & Technology; Technology; Life Sciences & Biomedicine; Engineering; Environmental; Environmental Sciences; Environmental Sciences & Ecology; Bio-logging; Demersal longlines; Depredation; Killer whales; Patagonian toothfish; Sperm whales; SPERM-WHALES; PHYSETER-MACROCEPHALUS; MARINE MAMMALS; ORCINUS-ORCA; PSEUDORCA-CRASSIDENS; FORAGING BEHAVIOR; FISHING PRACTICES; TOOTHFISH; 060205 Marine and Estuarine Ecology (incl Marine Ichthyology); 060201 Behavioural Ecology; 970106 Expanding Knowledge in the Biological Sciences; 830199 Fisheries - Aquaculture not elsewhere classified; MD Multidisciplinary; 3103 Ecology; Southern Ocean; Orca; Orcinus orca; Patagonian Toothfish; Physeter macrocephalus; toothed whales
• Online Access: http://hdl.handle.net/10536/DRO/DU:30121509; https://figshare.com/articles/journal_contribution/Evidence_of_deep-sea_interactions_between_toothed_whales_and_longlines/20758642

Toothed whales (odontocetes) feeding on fish caught on hooks in longline fisheries is a growing issue worldwide. The substantial impacts that this behaviour, called depredation, can have on the fishing economy, fish stocks and odontocetes populations, raise a critical need for mitigation solutions to be developed. However, information on when, where and how odontocete depredation occurs underwater is still limited, especially in demersal longline fisheries (fishing gear set on the seafloor). In the present study, we investigated depredation by killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus) on demersal longlines in the French Patagonian toothfish fishery (Southern Ocean). Using a combination of animal-borne behavioural and longline-attached data loggers, we demonstrated that both species are able to depredate longlines on the seafloor. This study, therefore, suggests that odontocetes whales-longline interaction events at depth may be unrecorded when assessing depredation rates from surface observations during hauling phases only. This result has implications for the management of fisheries facing similar depredation issues as underestimated depredation rates may result in unaccounted fish mortality in fish-stock assessments. Therefore, while further research should be conducted to assess the extent of deep-sea whale-longline interaction events during soaking, the evidence that depredation can occur at any time during the whole fishing process as brought out by this study should be considered in future developments of mitigation solutions to the issue.