Short-finned pilot whales modulate surfacing and breathing patterns more strongly in response to dives than in anticipation.

Diving marine mammals must allocate time between respiring at the surface and foraging underwater. Previous studies of optimal diving theory have attempted to predict such patterns, but the amount of time divers must spend at the surface before and after dives of varying durations remains difficult to assess. Here, we examined the surfacing and breathing patterns of short-finned pilot whales (Globicephala macrorhynchus) from biologger data to examine their use of anticipatory versus reactive strategies. We used linear mixed-effects models to examine the effect of dive characteristics on surface interval (SI) durations and breathing rate. Pilot whales increased SI duration before dives of increasing duration and after dives of increasing activity. Instantaneous breathing rates (fRs) of pilot whales demonstrated little anticipation but rather a strong reactive pattern seen by the modulation of fR in response to the previous rather than upcoming dive. During typical SIs, fR was predicted by time since previous dive, duration of the previous dive, time until upcoming dive, and activity of the previous dive. Short-finned pilot whales in our study area exhibit both benthic and pelagic foraging, which may compel anticipation when prey capture is predictable and reaction when prey capture is difficult to predict. The observed surfacing and breathing patterns therefore likely reflect a balance of the needs for blood gas homeostasis, aerobic metabolism, and the variability of foraging opportunities. An improved understanding of how animals make decisions about diving is critical for informing predictions of how they will contend with changing ocean landscapes.NEW & NOTEWORTHY A new study reveals how short-finned pilot whales balance the conflicting demands of foraging underwater with breathing at the surface. Using data from digital tags, scientists found that pilot whales rely more on surfacing strategies that react to the effort of a dive rather than anticipate. Their use of such strategies may reflect variation in the ability to predict prey capture in benthic and pelagic habitats.