Abstract
The feeding kinematics, suction and hydraulic jetting capabilities of captive harbor seals (Phoca vitulina) were characterized during controlled feeding trials. Feeding trials were conducted using a feeding apparatus that allowed a choice between biting and suction, but also presented food that could be ingested only by suction. Subambient pressure exerted during suction feeding behaviors was directly measured using pressure transducers. The mean feeding cycle duration for suction-feeding events was significantly shorter (0.15±0.09 s; P<0.01) than biting feeding events (0.18±0.08 s). Subjects feeding in-water used both a suction and a biting feeding mode. Suction was the favored feeding mode (84% of all feeding events) compared to biting, but biting comprised 16% of feeding events. In addition, seals occasionally alternated suction with hydraulic jetting, or used hydraulic jetting independently, to remove fish from the apparatus. Suction and biting feeding modes were kinematically distinct regardless of feeding location (in-water vs. on-land). Suction was characterized by a significantly smaller gape (1.3±0.23 cm; P<0.001) and gape angle (12.9±2.02°), pursing of the rostral lips to form a circular aperture, and pursing of the lateral lips to occlude lateral gape. Biting was characterized by a large gape (3.63±0.21 cm) and gape angle (28.8±1.80°; P<0.001) and lip curling to expose teeth. The maximum subambient pressure recorded was 48.8 kPa. In addition, harbor seals were able to jet water at food items using suprambient pressure, also known as hydraulic jetting. The maximum hydraulic jetting force recorded was 53.9 kPa. Suction and hydraulic jetting where employed 90.5% and 9.5%, respectively, during underwater feeding events. Harbor seals displayed a wide repertoire of behaviorally flexible feeding strategies to ingest fish from the feeding apparatus. Such flexibility of feeding strategies and biomechanics likely forms the basis of their opportunistic, generalized feeding ecology and concomitant breadth of diet.
Highlights
Adapted aquatic tetrapods represent an evolutionarily interesting experiment in organismal adaptation
Food items that projected from a hole were usually consumed first using suction, but food items were removed by grasping the food with the mouth and teeth, and removing the fish from the apparatus
Fish placed within the recessed cylinders initiated hydraulic jetting behavior, which was often alternated with suction generation, but could be used independently
Summary
Adapted aquatic tetrapods (e.g., marine turtles, penguins, and marine mammals) represent an evolutionarily interesting experiment in organismal adaptation. The terrestrial ancestors of marine mammals are thought to have exhibited a raptorial-type feeding mode [6] Part of their transition back to the sea likely involved an independent and secondary emergence of new mechanisms for underwater feeding. Our knowledge regarding these adaptations to underwater feeding and the feeding repertoire of aquatic mammals is limited to only a few species and much work needs to be conducted to understand feeding adaptations of marine mammals from a comparative perspective. The lack of feeding performance data for secondarily aquatic tetrapods is due to the fact that they spend considerable time at depth foraging and direct observation of prey capture is rare
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
