Table 4. — Major prey of harbor seals from seven geographic 

 areas in the Gulf of Alaska. Prey ranked in order of modified 

 Index of Relative Importance (IRI, see text footnote 3). Only prey 

 with IRI ^2 are included. [Occurrences = Percentage of 

 occurrences ± 95% confidence limits.] 



Area and prey 



IRI 



Occurrences 



Volume 



(%) 



Northeastern Gulf of Alaska (stomachs with contents 17: occurrences 39; 



volume 2,420 ml) 

 Walleye pollock 640 28.2±15.4 22.7 



Surf smelt 196 10.3±10.8 19.0 



Capelm 143 23.1 ±14.5 6.2 



Shrimps 131 2.6± 6.3 50.4 



Copper River Delta (stomachs with contents 14; occurrences 15; volume 



8.115 ml) 

 Eulachon 8,826 93.3 ±17.4 94.6 



Salmon 36 6.7±17.4 5.4 



Prince William Sound (stomachs with contents 83; occurrences 122; volume 



28,290 ml) 



Walleye pollock 

 Pacific herring 

 Squids 

 Octopus 

 Salmon 

 Capelin 

 Pacific tomcod 

 Pacific cod 

 Saffron cod 

 Eulachon 



1,375 



166 



77 



75 



33 



16 



5 



4 



3 



3 



29. 5± 



14.8± 



13. 1± 



13.9± 



3.3± 



4.1 ± 



1.6± 



4.9 ± 



2.5± 



1.6± 



8.5 

 6.7 

 6.4 

 6.6 

 3.6 

 3.9 

 2.7 

 4.2 

 3.2 

 2.7 



46.6 

 11.2 

 5.9 

 5.4 

 10.0 

 3.8 

 3.3 

 0.9 

 1.3 

 1.9 



Kenai coast (stomachs with contents 30; occurrences 52; volume 7,225 ml) 



Walleye pollock 

 Pacific herring 

 Pacific sandfish 

 Capelin 

 Pacific tomcod 



1,503 



247 



44 



19 



4 



40.4±14.3 



11. 5± 

 7.7± 

 5.8 ± 

 3.8± 



9.6 

 8.2 

 7.3 



6.2 



Lower Cook Inlet (stomachs with contents 17; occurrences 23; 



5.412 ml) 



Octopus 1.697 39.1 ±23.4 



Eulachon 532 17.4 ±18.6 



Shrimps 501 21, 7± 20.0 



Capelin 17 8.7±14.4 



Kodiak Island (stomachs with contents 102; occurrences 



42.685 ml) 



192; 



Octopus 



Capelin 



Walleye pollock 



Flatfishes 



Pacific cod 



Pacific sand lance 



Pacific herring 



Shrimps 



Salmon 



Sculpins 



Eulachon 



631 



323 



70 



63 



55 



9 



9 



8 



6 



3 



2 



21.4 = 



10. 9± 



12.0± 



10.9± 



8.3± 



8.3± 



2.1 ± 



3.6± 



2.1 ± 



4.2± 



0.5± 



6.1 

 4.7 

 4.9 

 4.7 

 4.2 

 4.2 

 2.3 

 2.9 

 2.3 

 3.1 

 1.3 



37.2 



21.5 



5.7 



3.3 



1.0 

 volume 



43.4 



30.6 



23.1 



1.9 



volume 



29.5 

 21.3 

 5.8 

 5.8 

 6.6 

 1.1 

 4.2 

 2.2 

 2.9 

 0.7 

 4.6 



Alaska Peninsula (stomachs with contents 6; occurrences 9; volumes 8,185 ml) 

 Octopus 929 33.3±41.8 27.9 



Walleye pollock 824 22.2±37.5 37.1 



Pacific sandfish 342 11.1 ±29.7 30.8 



Pacific cod 40 22. 2± 37.5 1.8 



Sculpins 26 11.1 ±29.7 2.3 



occurrences and volumes which was nearly twice 

 the percentages in other areas. 



Chi-square analyses of prey occurrences for 

 Kodiak Island and Prince William Sound indi- 

 cated that in Prince William Sound more walleye 

 pollock (P<0.01) were eaten than in Kodiak 

 (Table 5). In Kodiak there was higher utilization 

 (P< 0.05) of capelin than in Prince William Sound. 

 Octopus and Pacific cod were not utilized at 

 significantly different rates {P> 0.05). While sam- 

 ples were inadequate for statistical testing, it 

 appeared that more squids and Pacific herring and 



Table 5. — Comparison of occurrences of principal prey (N^4) 

 of harbor seals collected in Prince William Sound and the 

 Kodiak Island area. Statistical comparisons were made by 

 chi-square analysis. [% = Percentage ± 95% confidence limits; 

 — = Inadequate sample for statistical testing.] 



Kodiak 



Prince William Sound 



Prey 



No. 



% 



No. 



% 



>0.05 



< 0.05 

 >0.10 

 <0.01 



Octopus 41 21.4 + 6.1 17 13.9±6.5 



Squids 2 1.0±1.7 16 13.1±6.4 



Shrimps 7 3.6±2.9 1 0.8±2.0 



Pacific herring 4 2 1 ±2 3 18 14.8±6.7 



Salmon 4 2.1 ±2.3 4 3.3±3.6 



Capelin 21 10.9 ±4.7 5 4.1 ±3 9 



Pacific cod 16 8.3±4.2 6 4.9±4.2 



Walleye pollock • 23 12.0±4.9 36 29.5±8.5 



Sculpins 8 4.2±3.1 0.0 



Pacific sand lance 16 8.3±4.2 0.0 



Flatfishes 21 10.9±4.7 1 0.8±2.0 



Total occurrences 1 92 1 22 



fewer Pacific sand lances, flatfishes, and sculpins 

 were eaten in Prince William Sound than in 

 Kodiak. 



Salmon were found in the diet of harbor seals 

 from both Prince William Sound and the Kodiak 

 Island area only during the summer (Table 6). In 

 the Kodiak area, feeding on Pacific sand lance 

 appeared to be greatest in the fall while use of 

 capelin seemed to peak in the spring. Use of 

 Pacific herring by harbor seals appeared greatest 

 in the spring in Prince William Sound. 



Prey items were found in the stomachs of 13 

 harbor seal pups 2.5-11 mo of age and included 

 shrimps, capelin, Pacific tomcod, walleye pollock, 

 and Pacific sand lance. All items were <15 cm 

 total length. 



Discussion 



The high ranking of walleye pollock in the 

 harbor seal diet may have been a direct function of 

 its abundance. Pereyra and Ronholf* found that 

 walleye pollock was the dominant fish species in 

 the Gulf of Alaska, composing 459c by weight of 

 total fish stocks. Octopus, the second-ranked prey, 

 appears to be an important food of harbor seals 

 throughout the eastern North Pacific as nearly all 

 food studies have found them to be a major 

 component of the diet (Scheffer and Sperry 1931; 

 Imler and Sarber 1947; Fisher 1952; Wilke 1957; 

 Spalding 1964; Kenyon 1965; Bishop 1967). Five 

 of the six, top-ranked prey were off-bottom, school- 

 ing fishes. Use of this type of prey may minimize 



"Pereyra, W. T, and L. L. Ronholt. 1976. Baseline studies 

 of demersal resources of the northern Gulf of Alaska shelf 

 and slope. U.S. Dep. Commer., NOAA Processed Rep. NMFS 

 NWFC, 281 p. 



547 



