CALKINS: FEEDING BEHAVIOR OF ENHYDRA LUTRIS 



Table l.— Bottom-dwelling invertebrates of Montague Strait, 

 Alaska, and the percent of occurrence in the diet of sea otters. 



'Each of these pelecypods was identified as a dietary item one or more times, 

 but the relative frequency of use was not determined. 



''Observations were made on two different occasions of otters feeding on 

 mussels. The small mussels averaged around 2 to 3 cm each. This plus the fact 

 that the observation distance was up to 100 m made it impossible to get an 

 exact count. 



Shells of the snail Nucella ( = Thais) lamellosa; 

 cockle, Clinocardium nuttallii; and the rock oyster 

 or jingle, Pododesmus macroschisma, were abun- 

 dant in the study area. Tests of sea urchins were 

 rare. 



Octopuses consumed by otters ranged from 30 

 cm to 1 m across the tips of the tentacles. Crabs 

 (Telmessus cheiragonus) eaten ranged from 5 to 15 

 cm across the carapace. The clams consumed (Mya 

 truncata, Macoma inquinata, and M. incongrua) 

 were approximately 2 to 3 cm long, with Pro- 

 tothaca staminea andS. gigantea ranging from 2 to 

 10 cm long. Mussels (Mytilus edulis ) were 2 to 3 cm 

 long. Sea cucumbers measured 15 cm long and sea 

 stars (Evasterias troschelii) 20 to 30 cm across the 

 rays. 



From the 30 stations occupied along the inter- 

 tidal transects, a total of four clams (two Macoma 

 spp., oneS. gigantea, and one P. staminea) and 56 

 mussels were collected. 



Feeding Behavior 



Otters usually rose vertically so that the shoul- 

 ders were above the water surface before diving 

 (also see Limbaugh 1961). In water depths <4 or 5 

 m otters usually sank to shoulder level before roll- 



ing forward into a dive. In deeper water they ordi- 

 narily dove from the highest position of 

 emergence, presumably to provide greater down- 

 ward thrust. During the beginning of a dive, the 

 forelimbs were kept close to the body. One otter 

 often dove backward from a supine floating posi- 

 tion by kicking its hind flippers and arching its 

 back. The duration of feeding dives (average 66 s; 

 Table 2) was approximately the same as that ob- 

 served for sea otters in California (60-90 s; Lim- 

 baugh 1961). 



Otters in Montague Strait ate crabs as described 

 by Fisher ( 1939) for California otters and by Ken- 

 yon ( 1969) for Aleutian otters. Otters removed the 

 legs with one paw while clasping the crab to the 

 chest with the other paw. Kenyon (1969:116) re- 

 ports that "in the Aleutians the carapace was not 

 among the stomach contents," whereas Fisher 

 (1939:28) noted for California otters "when the 

 legs are finished, the body is eaten." While holding 

 otters in captivity prior to translocation from the 

 Montague Strait area during 1965 and 1966, the 

 animals were fed commercially available crabs 

 (Cancer magister) (Ed Klinkhart, Alaska Depart- 

 ment of Fish and Game, pers. commun.). The ot- 

 ters consistently ate the chelipeds first and then 

 the walking legs. Next the carapace was removed 

 and the body eaten. Finally the carapace was gen- 

 erally licked prior to discarding. Unconfined sea 

 otters occasionally bit the carapace but usually 

 discarded it after finishing the legs. Two crabs 

 were often taken during one dive. 



Otters dug out clams with their forepaws while 

 maintaining a head downward position (see Lim- 

 baugh 1961 for similar shallow-water feeding be- 

 havior of California otters). Holes or craters from 

 15 to 45 cm across and up to 50 cm deep, made by 



Table 2.— Results of 673 timed feeding dives of sea otters in 

 Montague Strait, Alaska, listed by depth. 



'Average depths for combined observations. 



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