Fin Whale (Balaenoptera physalus) Diel Dive Patterns in a Shallow Fragmented Foraging Habitat

Predators select foraging habitats to maximise energetic gains. However, habitat fragmentation can lead to increased costs from disturbances in high traffic urban environments. Understanding behavioural drivers of movement ecology is crucial for minimising conflict between evolutionarily selected foraging behaviours and novel anthropogenic stressors. In this study, 27 high-resolution biologging tags were deployed on fin whales in a shallow inner-shelf habitat south of the US east coast, where water depth can be less than the body length of the animal. The vertical movement patterns of the whales from diving overlapped with major shipping traffic. The whales spent > 67% of their time at depths shallower than the drafts of large ships (~10 m). The whales fed primarily during the day and remained very shallow at night (mean 5 m) while resting and travelling, possibly due to diel changes in vertical prey distribution. This natural behavioural pattern has become maladaptive with the introduction of anthropogenic traffic and puts them at extreme risk of injury and mortality in commercial shipping lanes at night, when mariners have limited visibility to detect them. These results underscore the importance of understanding baseline vertical movement patterns and behavioural trends to inform conservation efforts in fragmented environments.