PITCHER; PREY OF THE STELLER SEA LION 



RESULTS AND DISCUSSION 



Prey items were found in 153 of 250 sea lion 

 stomachs examined. Fishes made up 95.7%, 

 cephalopods 4.2%, decapod crustaceans <0.1%, 

 shelled gastropods <0.1% , and mammals <0.1% of 

 the volume of stomach contents (Table 3). Fishes 

 included 14 species representing 11 families. 

 Gadidae composed 59.7% of the total stomach con- 

 tents and occurred in 82.4% of the stomachs with 

 food. Walleye pollock was by far the dominant prey 

 composing 58.3% of the total volume of stomach 

 contents and occurring in 66.7% of the stomachs 

 with food. Cephalopod remains occurred in 36.6% 

 of stomachs with contents but made up only 4.2% 



Table 3. 



Prey 



-Stomach contents of 153 Steller sea lions collected in 

 the Gulf of Alaska. 



Occurrence' 



Volume 



No. 



95% C. I- 



ml 



Gastropoda: 



Snails 

 Cephalopoda 



Octopus. Octopus sp. 



Squids, Gonatidae 



Unidentified cephalopods 

 Decapoda 



Shrimps 



Snow crab. Chionoecetes sp. 



Spider crab. Hyas sp. 

 Unidentified invertebrates 

 Rajldae: 



Skate. Raja sp. 

 Clupeidae: 



Pacific herring, Clupea h. 

 pallasi 

 Salmonidae; 



Salmon, Oncorhynchus spp. 

 Osmeridae: 



Capelin, Mallotus villosus 

 Gadidae 



Saffron cod, Eleginus 

 gracilis 



Pacific cod, Gadus 

 macrocephalus 



Pacific tomcod, Microgadus 

 proximus 



Walleye pollock, Theragra 

 chalcogramma 



Unidentified gadid 

 Zoarcidae: 



Eelpout, Lycodes sp. 

 Scorpaenidae: 



Rockfishes. Sebastes spp. 

 Cottidae, sculpins 

 Agonldae: 



Sturgeon poacher, Agonus 

 acipenserinus 

 Tnchodontidae: 



Pacific sandfish, Tri- 

 chodon Irichodon 

 Pleuronectidae. flatfishes 

 Unidentified fishes 

 Harbor seal, Phoca v. 



nchardsi 



Total volume 



2 



56 



20 



35 



1 



11 



8 



2 



1 



1 



16 



16 

 126 



19 



102 

 2 



1.3 0.1-4.5 



36,6 29.5-45.0 



13.1 8.2-19.2 



22.9 16.7-30.4 



.7 .1-4.5 



7.2 



5.2 



1.3 



.7 



.7 



3.6-12.2 

 2.2-9.7 



.1-4.5 

 1-4.5 

 .1-4.5 



.1-4.5 



20 



15,777 



250 



15,507 



20 



130 



100 



20 



10 



10 



960 



10.5 5.8-15.8 76,920 



3.9 1.5-8.4 19,160 



10.5 58-15.8 27,755 



82.4 75.1-87.6 222,772 



1.3 .1-4.5 815 



12.4 7.4-18.1 3,471 



7 .1-45 680 



66.7 59.1-74.3 217,746 



13 1-4.5 60 



.7 



,1-4.5 



10 



2.6 1.0-7.1 3,030 



3 9 15-8.4 4,960 



.1-4.5 



60 



1.3 .1-4.5 300 



4.6 2.2-9.7 1,030 



2.6 1.0-7.1 40 



.1-4.5 



250 

 373,184 



<0.1 

 4.2 



<.1 

 4.2 

 <.1 

 <.1 

 <.1 

 <.1 

 <.1 

 <.1 



206 



5.1 



7.4 

 59.7 



.2 



.9 



2 



58.3 

 <.1 



<.1 



.8 

 1.3 



<.1 



<.1 



.3 



<.1 



<.1 



'Number of stomachs in which a prey item occurred. 



^Number of occurrences-'total number of stomachs with food (153). 



^95% confidence interval. 



"Total volume of a prey item/total volume of stomach contents. 



of the total volume of stomach contents. This ap- 

 parent disparity was probably the result of reten- 

 tion of cephalopod beaks in stomachs (Pitcher 

 1981) and the volumetric measurement was prob- 

 ably the most accurate measure of importance of 

 cephalopods in the sea lion diet. Invertebrates 

 other than cephalopods were found in 9.2% of the 

 stomachs with food but composed <0.1% of total 

 volume. Remains of two harbor seals were found in 

 one stomach. Major prey were ranked (Table 4) 

 using CRI. 



Table 4. — Rankings by combination rank index iCRI, see 

 Methods) of the 10 top-ranked prey of Steller sea lions collected 

 in the Gulf of Alaska. 



Rank 



CRI 



Prey 



Percentage 

 occurrence 



Percentage 

 volume 



1 

 2 

 3 

 4 

 5 

 6 

 7 

 8 

 9 

 10 



1 

 10 

 11 



16.5 

 28 

 38 

 51 

 57 

 76 

 88 



Walleye pollock 



Squids 



Pacific herring 



Capelin 



Pacific cod 



Salmon 



Octopus 



Sculpins 



Flatfishes 



Rockfishes 



66.7 



22.9 



10.5 



10.5 



12.4 



3.9 



13.1 



3.9 



4.6 



2.6 



58.3 



4.2 



20.6 



7.4 



.9 



5.1 



<.1 



1.3 



.3 



.8 



Predation on salmon, Oncorhynchus spp., and 

 capelin, Mallotus villosus, appeared to be largely 

 limited to spring and summer. Salmon occurred in 

 6 (12%) and capelin in 15 (30%) of 50 stomachs 

 containing food collected from April through Sep- 

 tember. Salmon was not encountered and capelin 

 was found only once (1%) in 103 stomachs contain- 

 ing food collected from October through March. 

 This likely reflected seasonal, nearshore distribu- 

 tion associated with spawning in these species 

 (Hart 1973; Jangaard 1974). I found a similar sea- 

 sonal pattern of harbor seal predation on salmon 

 and capelin in the Gulf of Alaska (Pitcher 1980). 



Pacific herring, Clupea harengus pallasi, and 

 squids were extensively used by sea lions in Prince 

 William Sound but appeared to be relatively un- 

 important in other areas. Fifteen of 16 stomachs 

 containing Pacific herring and 30 of 35 stomachs 

 containing squids were from Prince William 

 Sound both highly significant deviations {-^ = 

 12.30 and 16.61, P<0.001) from expected values 

 based on the distribution of stomachs containing 

 food (73 of 153 were from Prince William Sound). 

 Harbor seals also appeared to utilize more squids 

 and Pacific herring in Prince William Sound than 

 in other areas of the gulf, which was attributed to 

 differing water depths and bottom topography 

 (Pitcher 1980). 



469 



