Feeding kinematics, suction and hydraulic jetting capabilities in bearded seals (Erignathus barbatus)

Christopher D. Marshall,Christian Lydersen,Kit M. Kovacs

doi:10.1242/jeb.009852

Christopher D. Marshall, Christian Lydersen + Show 1 more

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https://doi.org/10.1242/jeb.009852

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Abstract

Feeding kinematics, suction and hydraulic jetting capabilities of bearded seals (Erignathus barbatus) were characterized during controlled feeding trials. Feeding trials were conducted both on land and in water, and allowed a choice between suction and biting, but food was also presented that could be ingested by suction alone. Four feeding phases, preparatory, jaw opening, hyoid depression and jaw closing were observed; the mean feeding cycle duration was 0.54+/-0.22 s, regardless of feeding mode (P>0.05). Subjects feeding on land used biting and suction 89.3% and 10.7% of the time, respectively. Subjects feeding in water used suction and hydraulic jetting 96.3% and 3.7% of the time, respectively. No biting behavior was observed underwater. Suction feeding was characterized by a small gape (2.7+/-0.85 cm), small gape angle (24.4+/-8.13 degrees ), pursing of the rostral lips to form a circular aperture, and pursing of the lateral lips to occlude lateral gape. Biting was characterized by large gape (7.3+/-2.2 cm), large gape angle (41.7+/-15.2 degrees ), and lip curling to expose the teeth. An excavation behavior in which suction and hydraulic jetting were alternated was used to extract food from recessed wells. The maximum subambient and suprambient pressures recorded were 91.2 and 53.4 kPa, respectively. The inclusion of suction data for phocids broadens the principle that suction feeding kinematics is conserved among aquatic vertebrates. Furthermore, bearded seals support predictions that mouth size, fluid flow speed, and elusiveness of prey consumed are among a suite of traits that determine the specific nature of suction feeding among species.

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

Introduction

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

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