The role of social transmission in the use of a new behaviour by killer whales in response to fisheries

Human exploitation profoundly impacts ecosystems but can also provide novel feeding opportunities to which animals may respond by learning new foraging behaviours. Among these, feeding on fisheries catch or byproduct, a behaviour termed ‘depredation’, has been observed in many large marine predator species globally. However, for social species, how social transmission influences both the acquisition of and the level of engagement in such behaviour by individuals within populations remains poorly understood. In this study, we analysed 18 years (2005–2022) of photo-identification data, with a combination of both social and diffusion models, to assess the role of social transmission in the acquisition of depredation by social units of the killer whale population of the Crozet Islands, as well as the extent to which social units engaged in this behaviour once acquired. We found that an increasing number of social units acquired depredation behaviour over time and that they did so through learning from other units and independent learning. We also demonstrate that during the years following this acquisition, their level of engagement in depredation was influenced by social preferences, with closely associated units showing similar levels of depredation and certain units acting as structural key nodes facilitating the transmission of depredation within the network. However, past the year when the entire population had acquired depredation, we found that factors other than social transmission came into play to explain heterogeneity in depredation levels observed across social units. Together, these findings highlight the role of social dynamics in shaping species' response to human-induced changes in their environment and in leading to intrapopulation behavioural heterogeneity that can have major implications for the long-term conservation of top marine predator populations.