y 



PRINCE 

 V^ «• i 5^ W I L L I A 



GULF OF ALASKA 



Figure l. — Montague Strait sea otter study area located in 

 Prince William Sound, Alaska. 



at least 50 km of the coast within the study area 

 seemed suitable for sea otters. The animals did not 

 frequent the areas with sandy beaches or shallow 

 estuaries. 



Feeding habits were studied at three main loca- 

 tions at Montague Island: a small lagoon (Ook- 

 shilk Lagoon, see de Laguna 1956) on the south 

 side of Stockdale Harbor, the area outside Ook- 

 shilk Lagoon to the north and west, and Port 

 Chalmers south of Stockdale Harbor. Ookshilk 

 Lagoon had water depths from 5 to 7 m and rock 

 and mud beaches grading to subtidal sand which 

 supported stands of eel grass, Zostera sp., and 

 rockweed, Fiicus sp. The area outside Ookshilk 

 Lagoon was characterized by water depths of 5 to 

 16 m, rock beaches and sand with reef shoals sub- 

 tidally, and Fucus sp. beach and subtidal flora. 

 Port Chalmers had water depths of 14 to 26 m with 

 rock beaches and subtidal sand with reefs and 

 shoals. Beach and subtidal flora in the Port Chal- 

 mers area consisted of Fucus sp. and kelp, 

 Nereocystis lutkeana. 



FISHERY BULLETIN: VOL. 76, NO. 1 



METHODS 



All observations on feeding habits were made 

 from advantageous locations on land. Spotting 

 telescopes with magnification of 15 to 60 x were 

 used to identify food organisms. Observation dis- 

 tances ranged from 20 to 500 m. The dimensions of 

 the organisms were estimated relative to the ot- 

 ters paws, which were estimated to average 4 cm 

 wide. Dimensions of octopuses were estimated 

 across the tips of the tentacles, relative to the 

 otter's body, and all sizes are reported in this man- 

 ner. No identification of organisms was attempted 

 beyond 100 m, but it was often possible to classify 

 food items by categories such as clam, crab, sea 

 star, etc., up to 500 m away. Dive and surface 

 feeding times for a total of 14 feeding periods were 

 measured with stopwatches. Timing of feeding 

 periods began when other activities ceased and the 

 otter dived for food and ended when the last bit of 

 food was eaten and some other activity began. 



Prey species were collected at low tide, and 

 taken to the University of Alaska for identifica- 

 tion. Clams were collected on a gravel beach in 

 Ookshilk Lagoon where otters fed. Work was 

 confined to 1 h before until 1 h after low tide ( —0.86 

 m). Ten transects were dug 25 m apart with each 

 transect running from the extreme high-tide mark 

 to the water's edge. Sample holes of approximately 

 0.25 m^ were dug at 5-m intervals along each 

 transect. Sample holes were dug to a depth of 25 

 cm. 



In areas where extensive observations were 

 made, water depths were measured using a 

 weighted line graduated at 25-cm intervals. 



RESULTS 



Types of Organisms Eaten 



All food organisms were bottom-dwelling in- 

 vertebrates from three major groups of organisms: 

 molluscs, crustaceans, and echinoderms. The per- 

 centage occurrence of prey organisms in the diet is 

 shown in Table 1. Five species of clams are found 

 in this area (Table 1), and all were eaten. Empty 

 shells and observations of feeding otters suggest 

 that Saxidomus gigantea is the clam most com- 

 monly eaten by otters. 



Several species were present in the area but 

 never observed to be eaten by otters (Table 1). 

 Each had been previously identified as food of sea 

 otters (Barabash-Nikiforov 1947; Kenyon 1969). 



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