126 



NORTH AMERICAN FAUNA 68 



Table 17. — Analysis of 75 fecal samples from the Shumagin Islands 



[15 samples were taken at Simeonof Island, 5-9 June 1960 and 60 at Eagle Harbor, Nagai 



Island on 16 June 1960] 



Food organism 



Number of 

 occurrences 

 (frequency) 



Percent of 

 fecal samples 

 having item 



Arthropoda : 



Crabs (Crustacea) 



MoUusca: 



Snails ( Gastropoda ) - 



Horse mussel Volsella volsella 



Mussel Mytilus edulus 



Clam (Pelecypoda) 



Subtotal 



Echinodermata : 



Sea urchin Strongylocentrotus drobachiensis. 

 Chordata : 



Fish 



Total. 



71 



94 



such as high winter mortality, indicates that the sea otter popu- 

 lation has approached its maximum size in the Shumagin Islands 

 as it has at Amchitka. It might therefore be concluded, in the 

 light of all available evidence (see Relative Values of Sea Otter 

 Foods), that the sea otters of Amchitka consume a large number 

 of sea urchins because other food resources have been depleted. 

 In areas where otter populations have not yet approached maxi- 

 mum size, food species more nourishing than sea urchins are 

 still abundant and the sea urchin may be eaten to a minor degree. 



The fecal analyses presented here give useful qualitative in- 

 formation on food habits. They show that the food habits of otters 

 in a crowded population differ from those in areas where crowding 

 is not a factor. It is, however, evident that stomach analyses are 

 necessary to reveal the food habits in their proper perspective. A 

 discussion of the method of ingestion of each group of food 

 organisms indicates in more detail why fecal examinations are of 

 only limited use in food habits studies of the sea otter. 



Food Quantities Required 



The food requirement of the sea otter is great. Captive juveniles 

 held on Amchitka Island during the 1957-59 study periods re- 

 quired from 25 to 30 percent of their body weight of food per day. 



The quantity of food consumed by captive adult otters did not i 

 vary according to season. The required amount for an adult male i 

 and female was similar, about 20 to 23 percent of the body weight 

 per day. The data are discussed in the section on the sea otter 

 "In Captivity." 



