Feeding Kinematics, Suction, and Hydraulic Jetting Performance of Harbor Seals (Phoca vitulina)

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

Experimental Feeding Platform.

<p>A. Feeding platform in place in the enclosure. B. Harbor seal feeding from feeding apparatus.</p

Experimental Subjects.

<p>Body length follows American Society of Mammalogists standards <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0086710#pone.0086710-American1" target="_blank">[77]</a>.</p>*<p>This subject lacks the small tail in between the hind flippers (average tail length: 8 cm).</p

Summary of Kinematic Variables.

<p>Values are means ± S.D., N = 5, 91 feeding events, GAOV = Gape Open Angle Velocity, GACV = Gape Angle Close Velocity.</p

Pressure Traces of Subambient Pressure Data.

<p>A series of six suction events of varying magnitude.</p

Pressure Traces of Suprambient Pressure Data.

<p>A series of seven hydraulic jetting events.</p

Loadings for Principal Components Axes 1–3.

<p>Log₁₀ transformed data, N = 5, 91 feeding events, GAOV = Gape Open Angle Velocity, GACV = Gape Angle Close Velocity.</p

Representative Kinematic Profiles of Suction vs. Biting.

<p>A. Frame from video during in-water suction feeding trial with overlaid spatial model stick figure. B. Plot of Gape (cm) for a single suction feeding trial. C. Plot of Gular Depression (cm) for a single suction feeding trial. D. Plot of Maximum Gape Angle (degrees) for a single suction feeding trial. E. Plot of Gape Angle Velocity (degrees/s; opening and closing) for a single suction feeding trial. F. Frame from video during on-land biting feeding trial with overlaid spatial model stick figure. G. Plot of Gape (cm) for a single biting feeding trial. H. Plot of Maximum Gape Angle (degrees) for a single biting feeding trial. I. Plot of Gular Depression (cm) for a single biting feeding trial. J. Plot of Gape Angle Velocity (degrees/s; opening and closing) for a single biting feeding trial.</p