STOMACH CONTENTS AND FECES AS 



INDICATORS OF HARBOR SEAL, 



PHOCA VITULINA, FOODS IN 



THE GULF OF ALASKA 



Traditional methods of investigating pinniped 

 feeding liabits have involved examination of 

 stomach contents from collected animals (Imler 

 and Sarber 1947; Spalding 1964; Fiscus and 

 Raines 1966). Recently, several scientists (Ainely 

 et al.^; Calambokidis et al.^) have used scats col- 

 lected from haulouts to study prey utilization of 

 the California sea lion, Zalophus californianus , 

 and the harbor seal, Phoca vitulina. This 

 technique may be valuable in situations where 

 killing animals is not feasible or desirable. No 

 comparative information has been available for 

 relating the results of scat analysis to stomach 

 content analysis. Between 1975 and 1978 I iden- 

 tified food remains in stomachs and in feces from 

 351 harbor seals collected along the Gulf of Alaska 

 coast from Yakutat Bay to Kodiak Island and was 

 able to compare the data resulting from both 

 sources. The sample of seals included both sexes 

 and spanned all age-classes. Seals were collected 

 during all months except December and January. 



Methods 



Seals were collected by shooting. Stomach con- 

 tents were removed in the field, wrapped in muslin 

 and preserved in a 10% Formalin^ solution. Fecal 

 material from large intestines was washed 

 through nested sieves (2.00 and 0.84 mm^) and 

 identifiable materials were recovered and pre- 

 served in 70% ethanol. Identifications of prey from 

 both stomach contents and feces were based 

 primarily on fish otoliths, cephalopod (squid and 

 octopus) beaks and shrimp exoskeletons; occa- 

 sionally vertebrae, preopercular bones, and intact 

 specimens found in stomachs also were used. All 

 otolith identifications were verified by John E. 



'Ainley, D. G., H. R. Huber, R. R. Le Valley, and S. H. Morrel. 

 1978. Studies of marine mammals at the Farallon Islands, Cal- 

 ifornia, 1976-77. Final report for MMC contract MM6AC027. 

 Available National Technical Information Service, 5285 Port 

 Royal Road, Springfield, VA 22151 as PB-286 603, 48 p. 



^Calambokidis, J., K. Bowman, S. Carter, J. Cubbage, R Daw- 

 son, T. Fleischner, J. Schuett-Hames, J. Skidmore, and B. Tay- 

 lor. 1978. Chlorinated hydrocarbon concentrations and the 

 ecology and behavior of harbor seals in Washington State wa- 

 ters. The Evergreen State Coll., Processed Rep., 121 p. 



^Reference to trade names does not imply endorsement by the 

 National Manne Fisheries Service, NOAA. 



FISHERY BULLETIN: VOL. 78, NO. 3, 1980. 



Fitch, California Department of Fish and Game, 

 Long Beach. 



Findings were compared by percentage of occur- 

 rences (number of stomachs or large intestines in 

 which a prey species was found) in the stomach 

 and fecal samples. 



Results and Discussion 



Spearman rank correlation analysis showed a 

 significant positive correlation (r^. = 0.79,P<0.01) 

 between the rankings of prey occurrences from 

 stomach contents and feces (Table 1 ). The greatest 

 discrepancy in rankings was for cephalopods 

 which were ranked second in the analysis of 

 stomach contents and ninth in the fecal analysis. 



Occurrences of individual prey categories from 

 stomach contents and feces showed good agree- 

 ment when analyzed with contingency tables (Ta- 

 ble 1). Only one significant statistical difference 

 (P<0.01) was found among 10 testable categories. 

 Cephalopods occurred more frequently (P<0.001) 

 in stomach contents than in feces. The x^ value for 

 cephalopods was so high (34.76) that rejection of 

 the null hypothesis seemed justified even in light 

 of potential type I errors resulting from multiple 

 tests. 



Cephalopods were identified primarily by their 

 chitinous beaks in both stomach contents and 

 feces. Beaks that were recovered in fecal material, 

 although sometimes fragmented, were easily rec- 

 ognized. Apparently most beaks were regurgi- 

 tated rather than passed through the intestinal 

 tract. Captive northern fur seals, Callorhinus ur- 

 sinus, which had been fed squid were observed 

 regurgitating beaks (Miller'*). Miller observed 

 that the beaks appeared to be "trapped" in the 

 stomach and were regurgitated at about 2-d inter- 

 vals. This is probably also true in harbor seals as I 

 have occasionally seen "wads" of beaks packed into 

 the pyloric ends of stomachs. This would tend to 

 exaggerate utilization of cephalopods in stomach 

 contents if the beaks persisted longer than re- 

 mains of other prey Therefore cephalopods are 

 apparently substantially underrepresented in 

 feces and probably somewhat overrepresented in 

 stomach contents. 



••Miller, L. K. 1978. Energetics of the northern fur seal in 

 relation to climate and food resources of the Bering Sea. Final 

 report for MMC contract MM5AC025. Available National Tech- 

 nical Information Service, 5285 Port Royal Road, Springfield. VA 

 22151asPB-275 296,32p. 



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