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NORTH AMERICAN FAUNA 68 



appear in recognizable form at all in droppings because shells are 

 not swallowed and the bones of some fish (Cyclopterichthys) are 

 soft and are digested. On the other hand, when sea urchins are 

 eaten some part or all of the test may be swallowed. The important 

 quantities of high protein food contained in mollusks and fish can- 

 not be evaluated by the examination of feces. 



It has been wrongly assumed that sea urchins held first-rank 

 importance as a sea otter food. Barabash-Nikiforov (1947) be- 

 lieved that sea urchins were essential to survival. There can be 

 no question but that where and when mature gravid sea urchins 

 are available they are an important food source. That they are not 

 essential to sea otter existence is demonstrated by: (1) A captive 

 sea otter was given no sea urchins for a period of 4 years and 

 remained in good health; (2) numerous captives held on Amchitka 

 refused to eat urchins after being introduced to a diet of fish; 



(3) each winter many juvenile sea otters (apparently incapable 

 of obtaining fishes) died of enteritis (probably induced by shock 

 or stress accompanying starvation) and were found to have the 

 remains of considerable numbers of sea urchins in the intestines ; 



(4) feces and stomachs of sea otters taken, for example, in the 

 Shumagin Islands, contained few, if any, sea urchin remains (al- 

 though sea urchins occur there). 



My conclusion is that sea urchins may, during their season of 

 reproduction in areas of abundance, rank high in importance as 

 a sea otter food source. Where an abundance of mollusks and 

 fish may be obtained, however, the sea urchin is at no time an 

 essential food species. The food value of the sea urchin may vary 

 from poor to good, depending on maturity and the season of re- 

 production. Mollusks and fish, however, when available and to 

 those animals able to obtain them, furnish an adequate and con- 

 sistently nourishing diet. Mollusks (37 percent) and fish (50 per- 

 cent), relatively high in calories, account for 87 percent by volume 

 of the sea otters' food at Amchitka. 



