Kinematics of gray whale ( Eschrichtius robustus ) foraging on infaunal ghost shrimp ( Neotrypaea californiensis )

Emergent technologies and integrative approaches have transformed our ability to understand organismal behavior, physiology and evolutionary ecology. Baleen whales (Mysticeti) have evolved the largest body sizes by filter feeding on dense aggregations of prey in diverse ocean ecosystems. Although the wide range of foraging modes and prey capture abilities among mysticetes has been well documented, the functional morphology underlying these relationships remains poorly understood. Gray whale (Eschrichtius robustus) morphology and ecological niche contrast starkly with those of closely related lunge-feeding rorqual species (Balaenopteridae), with gray whales foraging closer to the coastline using longer skulls and flatter mandibles in comparison to most rorquals. We used video and motion-sensing biologging tags to quantify the kinematics of gray whales feeding on infaunal ghost shrimp (Neotrypaea californiensis) in the shallow waters of the northern Puget Sound, Washington, USA. Tag-based kinematics were integrated with 3D models and morphological dimensions of the skull to calculate the skull area in contact with the seafloor during each feeding roll, resulting in an average minimum benthic contact area of 4.9±1.1 m2. Daily rates of feeding events (mean±s.d. 292±153) were comparable to those of lunge-feeding rorqual species despite using an average of 47.3% (weighted by deployment length) of the available high-tide feeding window. We posit that the paddle-like mandibles of gray whales reflect an adaptation for infaunal prey capture that may facilitate benthic suction filter feeding in shallow coastal habitats, potentially opening a unique coastal foraging niche among mysticetes.