Commercial fishing patterns influence odontocete whale-longline interactions in the Southern Ocean
Résumé
The emergence of longline fishing around the world has been concomitant with an increase indepredation-interactions by odontocete whales (removal of fish caught on hooks), resulting insubstantial socio-economic and ecological impacts. The extent, trends and underlying mechanismsdriving these interactions remain poorly known. Using long-term (2003–2017) datasets from sevenmajor Patagonian toothfish (Dissostichus eleginoides) longline fisheries, this study assessed the levelsand inter-annual trends of sperm whale (Physeter macrocephalus) and/or killer whale (Orcinus orca)interactions as proportions of fishing time (days) and fishing area (spatial cells). The role of fishingpatterns in explaining between-fisheries variations of probabilities of odontocete interactions wasinvestigated. While interaction levels remained globally stable since the early 2000s, they variedgreatly between fisheries from 0 to >50% of the fishing days and area. Interaction probabilities wereinfluenced by the seasonal concentration of fishing effort, size of fishing areas, density of vessels, theirmobility and the depth at which they operated. The results suggest that between-fisheries variationsof interaction probabilities are largely explained by the extent to which vessels provide whales withopportunities for interactions. Determining the natural distribution of whales will, therefore, allowfishers to implement better strategies of spatio-temporal avoidance of depredation.