MARSHALL, CD; KOVACS, KM; LYDERSEN, C ; Texas A&M University at Galveston, USA ; Norwegian Polar Institute, Troms�, Norway; Norwegian Polar Institute, Troms�, Norway: Suction and Hydraulic Jetting Forces Produced by Feeding Bearded Seals (Erignathus barbatus)

Bearded seals are thought to use suction as their primary feeding mode. This suggestion was, until recently, based only on anecdotal data. However, recent studies have confirmed that both suction and hydraulic jetting are important feeding behaviors of this species; the magnitude of these forces remained unknown. This study characterized suction and hydraulic jetting behaviors of bearded seals, and measured their magnitudes using a Millar MPC 350 pressure transducer inserted into a feeding apparatus. Pressure data from 70 feeding trials were collected with a portable electrophysiological recording system. Feeding behavior was videotaped and synchronized with physiological data using a pair of flashing LED lights whose optical pattern corresponded to a generated square wave pattern recorded as a separate channel. Bearded seals (N=2) used both suction and hydraulic jetting when feeding from the apparatus. The mean suction force recorded was -47.1 kPa (S.D.+ 25.7) and ranged from -3.2 to -108 kPa (N=392 suction events). The mean hydraulic jetting force recorded was 8.9 (S.D.+ 5.45) and ranged from 3.2 to 37 kPa (N=63 hydraulic jetting events). The mean duration of suction events (0.29 s, S.D.+ 0.12) was significantly greater (p <0.001) than the mean duration of hydraulic jetting events (0.13 s, S.D.+ 0.07). Suction events were often preceded by a small increase in pressure (preparatory phase) followed by relatively large negative pressures (suction phase). Suction capability of bearded seals are comparable to walruses, and validate anecdotal data that bearded seals are suction foragers. However, hydraulic jetting is an important component of the feeding repertoire of bearded seals.