FISHERY BULLETIN: VOL. 76, NO. 1 



Table 5. Frequency of occurrence of major food items in the diet of sea otters in Montague Strait, Alaska, compared with other 



locations. Organisms from the Commander Islands study are shown according to relative abundance as indicated by plus signs, 

 increasing plus signs indicate increasing abundance. 



Prior to this study, little use of rocks as tools for 

 opening clams had been observed in Alaska. Ken- 

 yon (1969) did not observe this phenomenon in the 

 wild, but saw a captive Alaskan otter pound a clam 

 against the side of its cement pool. Schneider 

 (pers. commun.) observed otters using rocks near 

 Amchitka, but considers this behavior uncommon. 

 Kenyon (1969) compared rock-pounding behavior 

 in the sea otter to the use of gravity by gulls (Larus 

 sp.) and ravens iCorvus corax). He also suggested 

 that tool-using behavior is derived from "chest 

 pounding, frustration behavior" (Kenyon 1969). 

 Otters will often pound clams on their chest when 

 the clams are particularly difficult to open (also 

 see Hall and Schaller 1964). 



Limbaugh (1961) noted that otters used the 

 same rocks on successive dives in California. This 

 was not observed in Montague Strait. 



Although Kenyon (1969:123) felt that "clams 

 which are buried are not dug from the bottom" and 

 that only those exposed to view or with exposed 

 parts are taken by the otters, otters in Montague 

 Strait frequently and successfully dug clams. 

 Saxidomus gigantea and Protothaca staminea are 

 found at depths of 8 to 45 cm along the North 

 Pacific coast (Fitch 1953: Quale and Bourne 1972: 

 Paul and Feder'*). Miller et al. (1975) presented 



"Paul, A. J,, and H. M. Feder. 1976. Clam, mussel and oyster 

 resources of Alaska. Univ. Alaska I.M.S. Rep, 76-4, Sea Grant 

 Rep, 76-6, 41 p. 



evidence which suggests California otters have 

 dug pismo clams, although no direct observations 

 have been made. 



When otters dig in soft sediments characteristic 

 of clam habitats, they undoubtedly locate clams by 

 touch due to obscured vision and, in fact, Kenyon 

 (1969) has shown that otters can locate food by 

 tactile sense alone. One blind captive otter located 

 food successfully and another normal individual 

 used only forepaws in the selection of a preferred 

 food (Mytilus edidis ) from a bucket of turbid water 

 that also contained small crabs iPachygrapsus), 

 and pebbles of various sizes. 



It is apparent that sea otters are able to subsist 

 on a wide variety of bottom-dwelling inverte- 

 brates and some fishes. Although they seem to 

 have local preferences, they tend to exploit what- 

 ever is available. As otter populations increase 

 they can effect drastic changes in bottom com- 

 munities. 



ACKNOWLEDGMENTS 



This study was made possible by funds provided 

 under Federal Aid in Wildlife Restoration, 

 Alaska, Project W-17-3, administered through the 

 Alaska Cooperative Wildlife Research Unit. I am 

 extremely grateful to Howard M. Feder, Univer- 

 sity of Alaska, for his advice and assistance and 

 tireless critical review of the manuscript; I thank 



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