Does optimal foraging theory predict the foraging performance of a large air-breathing marine predator?

Optimal foraging theory (OFT) suggests that air-breathing diving animals should minimize costs associated with feeding under water (e.g. travel time, oxygen loss) while simultaneously maximizing benefits gained from doing so (e.g. foraging time, energy gain). Humpback whales, Megaptera novaeangliae, foraging along the Western Antarctic Peninsula appear to forage according to OFT, but the direct costs and benefits in terms of their behaviours (e.g. allocation of time) have not been examined. We compared the foraging behaviour of humpback whales in this region inferred from multisensor high-resolution recording tags to their behaviour predicted by OFT time allocation models assuming the following currencies were being maximized: (1) the proportion of time spent foraging, (2) the net rate of energetic gain and/or (3) the ratio of energy gained to energy expended (i.e. efficiency). Model predictions for all three currencies were similar, suggesting any of these OFT models were suitable for comparison with the observed data. However, agreement between observed and optimal behaviours varied widely depending on the physiological and behavioural values used to derive optimal predictions, highlighting the need for an improved understanding of cetacean physiology. Despite this, many of the theoretical OFT predictions were supported: shallow dives (i.e. <100 m), which were short and executed most frequently, yielded the highest proportions of foraging time, and the greatest net rates of energy gain and were the most efficient. In addition, dive and foraging times increased in duration rapidly with increasing maximum dive depths to approximately 100 m and then at lower rates with deeper dives. Our findings offer a thorough examination of the applicability of time allocation OFT models to the behaviours of a large, air-breathing, diving predator and provide insights into the foraging ecology and physiology of humpback whales in the Western Antarctic Peninsula.

Duke Scholars

Author Douglas Nowacek Marine Science and Conservation