Society of Integrative and Comparative Biology Abstract 2005

Behavioral Performance of Feeding in Kogia and Tursiops (Odontoceti: Cetacea): Ram vs. Suction Feeding Strategies

BLOODWORTH, B.E. Texas A&M Univ., Galveston,
MARSHALL, C.D. Texas A&M Univ., Galveston

The feeding performance of two bottlenose dolphins (Tursiops truncatus) and one juvenile pygmy and dwarf sperm whale (Kogia breviceps and K. sima) was compared during controlled feeding trials. Feeding behavior was characterized and a Ram-Suction Index (RSI) measured. The feeding behavior of both genera was composed of four phases: preparatory (Phase I), jaw opening (Phase II), gular depression (Phase III) and jaw closing (Phase IV). The mean Kogia total feeding cycle duration (533 ms; SD±150) was shorter than the mean for Tursiops (847 ms; SD±349). The mean maximum gape angle was greater for Kogia (56.6º; SD±3.3) than for Tursiops (25.5º; SD±8.5). The mean Kogia RSI (-0.04; SD±0.378) was significantly less (p<0.001) than the mean Tursiops RSI (0.71; SD±0.14), indicating a suction and ram-based strategy for Kogia and Tursiops, respectively. The significantly shorter (p<0.05) Kogia jaw opening phase (172 ms; SD±75) supports the RSI results. Tursiops displayed two feeding behaviors, a Type I in which the mandibles open near to a food item and a Type II in which gape was near maximum while the subject was greater than one meter away from food. Total feeding cycle duration and RSI of Type I behavior (693 ms; SD±273 and 0.65; SD±0.15) were significantly different (p<0.001) from Type II behavior (1135 ms; SD±297 and 0.79; SD±0.05). Significant differences in RSI also existed between Kogia (-0.04; SD±0.378), Type I (0.65; SD±0.15) and Type II (0.79; SD±0.05) feeding behaviors. The results suggest odontocetes demonstrate a wide range of feeding strategies along the ram-suction continuum not previously characterized. Variability among individuals can be high and multiple feeding behaviors are possible even within a single genus (i.e., Tursiops).

Suction and Hydraulic Jetting Forces Produced by Feeding Bearded Seals (Erignathus barbatus)

Marshall, C. D. Texas A&M University at Galveston, USA;
Kovacs, K. M. Norwegian Polar Institute, Tromsø, Norway
Lydersen, C., Norwegian Polar Institute, Tromsø, Norway

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.