Hopkins Marine Station Student Paper

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(full paper is archived in the Miller Library)

Title: Inter-individual variation and effect of wave height on foraging upon mussels by the California Sea Otter, Enhydra lutris
Student Author(s): Randle, Steven W.
Faculty Advisor(s): Watanabe, James
Pages: 32
Location: Final Papers Biology 175H
Date: June 1996
Abstract: Foraging on intertidal mussels by the California sea otter, Enhydra lutris, was examined to determine its effects on the mussel beds around Point Cabrillo, Pacific Grove, CA. Frequencey of success for foraging on mussels and foraging on other types of prey were observed, as well as the mean number of mussels removed and eaten by otters. The average duration of individual feeding bouts and the average number of dives per minute were measured in order to discover the mean number of mussels removed a day. These data were analyzed comparing individual otter eating habits. Frequency of success for mussel (94.53%) and non-mussel foraging (69.05%) and were significantly different (p<<0.001). There was also significant inter-individual variance in mean number of mussels removed (p<<0.001) and mean number of mussels eaten (p<<0.001) among different otters. Foraging on mussels in relation to increasing wave heights showed a significant decrease in number of mussels removed (p<0.005) and mussels eaten (p<0.001) as wave height increased. Success ratio also decreased as wave height increased (p<0.01). In addition, the frequency of foraging on mussel beds increased with tidal height and was more prevalent in the early evening compared to the other times of the day.
Because otters have such a high metabolic rate, they must eat up to 25% of their body weight daily. Using previously published data (Costa, 1978), mean number of mussels per dive, and average number of dives per minute, a sea otter would have to forage for mussels for approximately 294 minutes per day to obtain sufficient kilocalories.