Behaviour and population structure of baleen whales in the Northeastern Pacific Ocean

Understanding the behaviour and population structure of baleen whales is essential for their conservation in an era of escalating anthropogenic pressures. This thesis combines behavioural ecology and population genomics to investigate humpback whales (Megaptera novaeangliae) and fin whales (Balaenoptera physalus) in the Northeastern Pacific, focusing on populations in British Columbia, Canada. I situated this work with a positionality and reflexivity statement, establishing an anti-colonial research praxis as integral to conducting ethical marine mammal science. First, I examined the diffusion of bubble net feeding (‘bubble netting’), a specialised foraging tactic in humpback whales, using two decades of photo- identification data in Gitga’at First Nation territory. Network-based diffusion analyses revealed strong support for social learning of the behaviour using static social networks, however the cooperative nature of bubble netting prevented homophily from being fully excluded. Nonetheless, the rapid population-wide uptake of bubble netting suggests this behaviour has contributed to the recovery of the population. Second, I demonstrate that exhaled respiratory vapour, or ‘blow’, samples from baleen whales can yield whole low-coverage nuclear genomes and high-coverage mitochondrial genomes. Using this non-invasive approach, I generated the first population-level genomic dataset for North Pacific humpback whales and applied this to explore population structure. Finally, I assessed population structuring of fin whales in British Columbia using 116 whole genomes, collected between 1998 and 2023. Although standard tests suggest panmixia, I extended a Hill numbers–based genetic diversity framework to whole-genome data and revealed signals for substructure. Levels of genomic differentiation indicate that British Columbian fin whales may represent a demographically independent unit from the wider eastern North Pacific. Together, these studies advance understanding of baleen whale sociality and population structure, while introducing novel genomic tools and datasets. This integrative approach underscores the need to combine behavioural ecology, genomics, and ethical research practices for holistic conservation of cetaceans in rapidly changing oceans.