THE SEA OTTER IN THE EASTERN PACIFIC OCEAN 111 



than those subsisting primarily on invertebrates. Also, the bones 

 of ''fish-eaters" are white but the bones of those otters utilizing 

 invertebrates — including many sea urchins — are stained purple 

 by the biochrome polyhydroxynaphthoquinone (Scott, in Fox, 1953, 

 footnote p. 195). 



Much indigestible material is swallowed incidentally in the con- 

 sumption of nourishing food. Part of the test of almost every sea 

 urchin eaten is crushed by the postcanines and swallowed. Many 

 stomachs contain scraps of red and brown algae. Seaweeds, as 

 Barabash-Nikiforov (1947) and Fisher (1939) indicate, cannot be 

 considered an otter food. This material appears in the feces un- 

 altered in appearance, except for the wear and abrasion en- 

 countered during passage. I have often seen such scraps of kelp 

 eaten when entangled among the spines of sea urchins. Its occur- 

 rence in stomachs is accidental. 



Small pebbles, gravel, and bits of hard clay occurred in 14 per- 

 cent of 475 stomachs from Amchitka. One stomach contained 325 

 small stones. Stones are also commonly found in the stomach of 

 fur seals and sea lions (Eumetopias and Zalophus) and no sure 

 explanation of their presence is known. Although the "gastroliths" 

 of pinnipeds are usually waterworn or smooth, the stones we 

 found in sea otter stomachs often looked as if they had been 

 freshly broken apart; they were seldom waterworn or smooth. 

 No reason for the swallowing of this indigestible material is 

 known. 



After food has been selected from the substrate, it is stored for 

 transportation to the surface in folds of loose skin (fig. 11) which 

 extend from the axilla across the chest (see Kirkpatrick et al., 

 1955; Barabash-Nikiforov, 1947). If only enough food is gathered 

 to fill the pouch on one side, it is stored under the left foreleg and 

 paw. If a large quantity is gathered, it may be stored and carried 

 in the chest pouches under both forelegs. 



When an otter captures a large octopus or fish and satisfies its 

 appetite before it consumes the entire organism, it often sleeps on 

 the water's surface with the remains of such an uneaten meal 

 clasped to its chest. After sleeping for awhile, the otter awakens 

 and continues to eat. Uneaten food, however, is not retained for 

 an extended period. After the animal has nibbled its food inter- 

 mittently for perhaps 2 hours, and then begins to groom, the food 

 is forgotten and allowed to sink. Captives retrieve discarded food 

 and again eat after grooming and resting. 



On occasions when we have pursued otters with an outboard 

 motor-powered dory we have interrupted their feeding. When this 



