Doroff and DeGange: Prey composition and foraging success of Enhydra lutris 



705 



prey populations (Kvitek et al., 1992) 

 and an opportunity to assess changes 

 in sea otter foraging characteristics 

 (prey composition, forage success, prey 

 size and biomass) as they relate to the 

 duration the habitat had been occupied. 

 We describe the foraging characteristics 

 of sea otters in relation to the length of 

 habitat occupancy along the Kodiak Ar- 

 chipelago. 



Methods 



Study area 



Study areas in the Kodiak Archipelago 

 were chosen in regions that differed in 

 the number of years since sea otters had 

 reoccupied the habitat (Fig. 1). We cat- 

 egorized the areas following Kvitek et 

 al. (1992) as established (occupied for 

 >25 years), intermediate (occupied for 

 5-15 years), and frontal (occupied for 

 <5 years) based on sea otter surveys 

 (Lensink, 1962; Kenyon, 1969; Schnei- 

 der 1 ; Simon-Jackson 23 ; and interviews 

 with local inhabitants). Established 

 study sites were on southern Shuyak 

 and northern Afognak islands, interme- 

 diate study sites were located between 

 southern Afognak and northern Kodiak 

 islands, and frontal study sites were 

 southeast of Afognak and Raspberry is- 

 lands. Study sites had broad expanses 

 of shallow water (<20 m) with prima- 

 rily sand and gravel sediments support- 

 ing infaunal bivalve assemblages 

 (Kvitek et al., 1992). 



Foraging observations 



Observations of foraging sea otters were made from 

 shore with the aid of lOx binoculars and 40-80x tele- 

 scopes (Questar Corp., New Hope, PA). Foraging data 

 were collected by focal animal sampling (Altmann, 

 1974). Repeated dives were recorded for a focal ani- 

 mal while the animal remained in view and contin- 

 ued to forage (Calkins, 1978). All observations were 

 made on unmarked animals that were within ap- 

 proximately 1 km of shore. Data were collected dur- 

 ing June— October 1987 and during March, June, and 

 September of 1988 during daylight hours and dur- 

 ing various tidal states. 



Data for each recorded dive included sex and age 

 class of otter, presence of a pup, number of prey items 



ESTABLISHED 



INTERMEDIATE 



Figure 1 



Study areas for observations of foraging sea otters, Enhydra lutris, 

 in established (occupied >25 yr), intermediate (occupied 5-15 yr) and 

 frontal (occupied <5 yr) areas during 1987 and 1988 in the Kodiak 

 Archipelago, Alaska. 



obtained, identification of prey (classified to lowest 

 possible taxon), and categorization of prey size (small 

 <5 cm, medium 5-9 cm, and large >9 cm). Size class 

 of prey was estimated relative to the mean forepaw 

 width ( 4.5 cm ) and mean skull width ( 10 cm) for adult 

 sea otters (Johnson 6 ). Adult otters were classified as 

 male, female, female with pup, or unknown sex. Ju- 

 veniles that were estimated to be <2 years of age 

 were differentiated from adults by their small body 

 size (estimated to be <18 kg) and dark pelage. For- 

 age data on pups still associated with their mother 

 were not collected. Forage dives were classified as 

 successful (prey captured), unsuccessful (no prey 

 captured), or of unknown success (observer could not 

 determine if prey were captured). 



Johnson, A. M. 1987. Sea otters of Prince William Sound, Alaska. 

 U.S. Fish and Wildlife Service, Alaska Fish and Wildlife Re- 

 search Center, Anchorage, Alaska. Unpubl. rep., 87 p. 



