Hopkins Marine Station Student Paper

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Title: Underwater observations of sea otter foraging behavior
Student Author(s): Mackey, Fallon
Faculty Advisor(s): Pearse, John
Pages: 51
Location: Senior Thesis UC Santa Cruz
Date: August 1982
Abstract: It hasn't been long since the 'rediscovery' of a relict population of sea otters (Enhydra lutris) on the Big Sur coast in California first captivated the scientific community (Bolin 1938). Since that time California sea otters have reoccupied 200 miles of coastline and presently number less than 2,000 animals.
They are listed as threatened speces, primarily because a potential oil spill from increased tanker traffic and offshore oil reserve development within the sea otter's range could have fatal consequences. A lumber spill in waters off central California during the winter of 1978 spread through most of the otter's range within 4 weeks. The movement rates of the lumber were similar to those of oil slicks observed elsewhere and indicated that a major oil spill could expose signicicant numbers of sea otters to oil contamination (Van Blaricom and Jameson 1982). The U.S. Fish and Wildlife Service has implemented a recovery plan which includes a possible translocaton of animals to San Nicolas Island in the hopes of establishing a second viable population.
Unlike most marine mammals that have a layer of insulationg blubber, sea otters rely on their fur, the thickest of any mammal, to protect them from the cool marine environment. In order to fuel their high metabolism, sea otters consume as much as 25% of their body weight in food per day (Kenyon 1969 Costa 1978).
The sea otter is a unique member of the family Mustelidae, a nocturnal and secretive clan, in that its foraging behavior can be esaily observed. The majority of research has been based on 'shoreside' observations utilizing binoculars or spoting scopes, and very few investigators have used SCUBA in an attempt to observe sea otters engaged in the pursuit of prey. This is not surprising since sea otters can easily evade divers. Attempts to gain enough underwater observtions to draw any definite conslusions beyond those which can be made from shore observations should expect a low success rate. This study, carried out from 6 September to 22 November 1980, obtained about three hours of actual underwater observation of sea otters for 84 hours of field time when water visibility was acceptable (+ 6 m/20 ft.) and we were prepared to dive. Field time includes time spent in an inlfatable raft seeking out approachable subjects as well as unsuccessful activity in full suite above and below the waters' surface. This can be expressed as a success rate of 3.8%.
This paper has several purposes: 1) to review prior investigations of sea otter foraging; 2) to give the results of shore observations carried out at Point Cabrillo, Pacific Grove; 3) to report underwater observations; 4) tp present suggestions for future work, including the value of underwaer food transfer.