FISHERY BULLETIN: VOL. 76, NO. 1 



the otters in this process, were abundant in inter- 

 tidal and subtidal areas with gravel or sand bot- 

 toms. 



A male otter was observed feeding on clams 

 about 3 to 5 cm long; 38 clams were consumed in 35 

 min (1.08/min). A female and a large pup, ob- 

 served at the same location, fed on clams of the 

 same size range as those eaten by the male. Only 

 the female successfully brought up clams al- 

 though the pup dove with her. Together, they con- 

 sumed 56 clams in 65 min (0.86/min). Both adults 

 brought up as many as three clams per dive. 



Generally, clams 3 to 5 cm long were eaten in- 

 tact including the shell. The otter pushed each 

 clam into its mouth, crushed the shell, and swal- 

 lowed the entire clam immediately. Larger clams 

 (5 to 10 cm long) were cracked with the cheek 

 teeth, usually breaking one valve in half (see Mil- 

 ler et al. 1975). This has also been observed in 

 Monterey Bay (H. Feder pers. commun.). Valves 

 were then forced open by a rotating motion or were 

 pulled apart with the paws, and the soft parts 

 scooped or bitten out with the incisor teeth. 



Large males were occassionally able to crack 

 clams >10 cm with their cheek teeth and pull the 

 valves apart with their paws. However, they typi- 

 cally opened larger clams by pounding them 

 against each other or against a rock until the shell 

 was fractured and the valves forced open. The size 

 of the rocks ranged from 7 to 15 cm long but there 

 was no preference for shape. 



Otters often used stones as tools for opening 

 hard shelled invertebrates such as clams (Fisher 

 1939; Limbaugh 1961; Hall and Schaller 1964). 

 With the stone lying on the otter's chest, the clam 

 was struck against it with several quick, hard 

 blows until the shell or the hinge was broken. 

 Otters were typically nonselective when striking 

 the clam against a rock; however, one otter consis- 

 tently struck the hinge area which usually sepa- 

 rated after three or four blows. A rock was not used 

 more than once. Each rock was always discarded 

 immediately by allowing it to slip off the chest. 



Otters obtained mussels by pulling up holdfasts 

 of Laminaria sp. to which the bivalves were at- 

 tached. The animal then floated with the algal 

 frond across the body and picked individual mus- 

 sels off with its forepaws and ate them whole. 

 Otters never consumed algal material. 



Octopuses were eaten completely. One female 

 consumed an octopus (60 cm across the tips of the 

 tentacles) in slightly more than 6 min. The otter 

 held the body of the octopus in its paws and bit into 



an arm or the body while pulling away with its 

 head and pushing away with its paws. This left a 

 piece of octopus in the mouth, which was pushed in 

 while the remainder was held in the otter's axilla 

 or against the chest. This procedure was repeated 

 until the entire octopus was eaten. Pieces dropped 

 during the feeding process were retrieved. 



Sea stars were not a preferred food. According to 

 Kenyon( 1969: 119), "the otter usually tears off and 

 eats one or two arms of a sea star . . . and discards 

 the remainder." Otters in Montague Strait fed in a 

 similar manner. Kenyon (1969) reported several 

 species of sea stars are eaten by otters in the Aleu- 

 tians. Only one sea-star species (Evasterias tros- 

 chelii) was taken by otters in the present study, 

 although others were available (Dermasterias im- 

 bricata and Pycnopodia helianthoides). 



Sea cucumbers were rarely eaten and were also 

 apparently of minor importance to Aleutian otters 

 (Kenyon 1969). Sea cucumbers were torn open, a 

 portion of the viscera and part of the body wall 

 eaten, and the remainder discarded. 



Feeding periods ranged from 25 to 147 min, av- 

 eraging 84.5 min. Elapsed times for eating at the 

 surface during the 14 feeding periods ranged from 

 17 s for a clam to 6 min for an octopus, with a mean 

 value of 38 s for all foods (see Table 2 for diving 

 times and Table 3 for average consumption times 

 of each food item). 



Table 3. — Range and mean of feeding times for individual food 

 items measured in seconds for sea otters in Montague Strait, 

 Alaska. 



DISCUSSION 



The sea otter is an opportunistic feeder 

 throughout its range. It generally feeds on bot- 

 tom-dwelling invertebrates, but may select fishes 

 if the invertebrate supply is depleted (Kenyon 

 1969 in Table 4). Mollusks were the most impor- 

 tant food of otters in California and Montague 

 Strait, echinoderms are apparently most impor- 

 tant in the Commander Islands, and fishes most 

 important in the Aleutians (Table 5). Crustaceans 

 were second in importance at Pico Creek, Calif., 



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