Doroff and DeGange: Prey composition and foraging success of Enhydra lutris 



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(class Ascidiacea), and kelp (primarily kelp hold-fasts 

 with small unidentified invertebrates attached). Uni- 

 dentified prey constituted 4—6% of prey per area. 



The proportion of forage dives resulting in the cap- 

 ture of clams, mussels, and crabs did not differ among 

 study areas for adults. For all study areas combined, 

 adult and juvenile sea otters differed in the propor- 

 tion of forage dives capturing clams (x 2 =13.35, df=l, 

 P<0.001) and mussels (x 2 =10.40, df=l, P=0.001) but 

 not crabs {% 2 =3.22, df=l, P=0.07). The median pro- 

 portion of dives resulting in the capture of clams 

 ranged among study areas from 0.62 to 0.85 for adults 

 and from 0.00 to 0.52 for juveniles. Conversely, me- 

 dian values for mussels ranged from 0.00 to 0.93 for 

 juveniles and was zero for adults. Crabs were cap- 

 tured infrequently and the median proportion of dives 

 capturing crabs was zero for both age classes. 



Forage success did not differ among study areas 

 (F=0.52, df=2, P=0.59) nor among sex classes (P=2.22, 

 df=2, P=0.12) within areas for adults; the interac- 

 tion between sex class and area was not significant 

 (P=0.50, df=4, P=0.74). Mean forage success for all 

 study areas combined was 89% for adults and 90% 

 for juveniles and did not differ significantly (<=-0.59, 

 df=107,P=0.56) (Table 1). 



Mean number of prey captured per dive by adults 

 in established, intermediate, and frontal areas dif- 

 fered among areas (l.&tl.O, 1.1±0.4, and 1.2±0.8, 

 respectively) (P=3.88, df=2, P=0.02) but not among 

 sex class (P=0.98, df=2, P=0.38); the interaction be- 

 tween sex class and area was not significant (P=1.00, 

 df=4, P=0.41). Juvenile sea otters, did not differ in 

 the mean number of prey captured per dive among 

 study areas (P=0.55, df=2, P=0.59) (Table 1). 



In the established area, 92% (rc=526) of the clams 

 captured by sea otters were small (<5 cm), and 8% 

 were medium (5-9 cm). In intermediate and frontal 

 areas, however, only 27% (n=943) and 38% («=1,039) 

 of all clams captured were small and the majority 

 were medium sized. The mean caloric content of 

 Saxidomus captured by adult otters per forage dive 

 in established, intermediate, and frontal areas was 

 estimated to be 10 kcal, 21 kcal, and 21 kcal, respec- 

 tively (Table 2). 



Discussion 



The composition of the diet was similar for sea ot- 

 ters in the Kodiak Archipelago among forage areas 



