Context-driven communication during deep-sea foraging in a social toothed whale

Social deep-diving odontocetes face the challenge of balancing
near-surface proximity to oxygen and group members with foraging in the
deep sea. Individuals rely on conspecifics for critical life functions,
such as predator defence, but disperse during foraging to feed
individually. To understand the role of social acoustic mediation during
foraging in deep-diving toothed whales, we investigated the context of
social burst-pulse call production in Risso’s dolphin (Grampus griseus)
using biologgers. Dolphins produced context-specific burst-pulses
predominantly during daytime foraging, preceding or following foraging
dives and in the early descent of daytime deep dives. Individuals applied
differential short and long burst-pulse calls intended for either
near-surface receivers (horizontal transmission) or deep-foraging
receivers (vertical transmission). Our results show that deep-diving
toothed whales are reliant on acoustic communication during certain
foraging contexts, to relay information, including foraging conditions or
an individual’s location. Moreover, they accentuate the importance of
maintaining acoustic contact with conspecifics, specifically when
dispersed during deeper foraging. It also signifies that our oceanic top
predators may be specifically vulnerable to the current strong increase in
anthropogenic noise. Potential masking of the signals from group-members
communicating at a distance could undermine their social cohesion, and
hence their capacity to maintain vital life functions.