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First published online May 21, 2007
Journal of Experimental Biology 210, 1960-1970 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02767

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Diving and foraging energetics of the smallest marine mammal, the sea otter (Enhydra lutris)

Laura C. Yeates^*, Terrie M. Williams and Traci L. Fink

Department of Ecology and Evolutionary Biology, 100 Shaffer Road, University of California, Santa Cruz, CA 95060, USA

View larger version (7K): [in this window] [in a new window]   Fig. 1. Frequency distribution for the duration of foraging dives by wild and captive sea otters. For wild otters (white bars), dive durations were recorded during 24-h observation periods to assess daily activity budgets as well as during focal foraging bouts. For captive otters (black bars), dive durations were recorded during forage diving in a water tower.

View larger version (8K): [in this window] [in a new window]   Fig. 2. Rate of oxygen consumption during rest and activity by sea otters. Height of each bar represents the mean value for each behavioral state; vertical lines denote + 1 s.d. Numbers in parentheses indicate sample sizes. Note that foraging and grooming oxygen consumption rates were measured in post-prandial otters. The remaining rates were measured in post-absorptive otters. All rates measured in this study were statistically different (see text). Data represented by gray bars are from Williams (Williams, 1989) and were not included in statistical comparisons.

View larger version (5K): [in this window] [in a new window]   Fig. 3. Total oxygen consumed during controlled single dives in relation to dive duration for captive adult sea otters. Each point represents a single dive by the otter. The thin line is the least squares curvilinear regression through the points as described in the text. Note that the values are the amount of oxygen used for performing a dive above that required for maintenance costs.

View larger version (7K): [in this window] [in a new window]   Fig. 4. Total cost of foraging (bar height) in relation to prey type for adult sea otters. Each bar is subdivided into the energy expended for maintenance costs based on resting metabolic rate (black), locomotor costs calculated from the difference between single dive costs and resting costs (gray), and foraging/prey handling costs (white). The latter was calculated from the difference between total measured foraging metabolism and the two other costs, and includes the energy expended for locating, carrying and consuming the prey items as well as heat increment of feeding. Vertical lines above bars represent +1 s.d. The numbers in parentheses are the number of trials.

View larger version (4K): [in this window] [in a new window]   Fig. 5. Field metabolic rate (FMR) in relation to body size for marine mammals. Points represent male and females of each species where available. Marine mammals include sea otters from the present study (triangles), and phocid seals (squares), otarids (diamonds), and odonticetes (circles) from Williams et al. (Williams et al., 2004a). The thin line through the points is the least squares allometric relationship and is described by FMR=1367.7mass0.76 (N=24, r2=0.949, P<0.001) from Williams et al. (Williams et al., 2004a).