Trites et al Diets of Eumetopias jubatus in Southeast Alaska 



239 



groups per scat) were compared by using analysis 

 of variance. 



Associations between prey groups recovered from 

 individual scats were identified by calculating partial 

 correlation coefficients for each pair of prey groups 

 by using presence and absence data with each scat 

 as a replicate (Zar, 19961. This analysis was per- 

 formed for all scats collected at the three rookeries 

 during the summer and for all scats collected at the 

 haulouts during autumn-spring. Partial correlations 

 were considered significant at P=0.05. Prey associa- 

 tions were illustrated by using the hcliist function of 

 S-Plus 2000 (Mathsoft Inc., Seattle, WA) and using 

 the "average" clustering method and the distance 

 between two prey groups as equal to 1 minus the 

 partial correlation coefficient of those two prey. 



Results 



A total of 61 species of prey were identified from all 

 of the scats examined. The most common prey (i.e., 

 those that occurred in more than 5% of all the scats 

 examined) in order of frequency were walleye pol- 

 lock. Pacific herring, sand lance, salmon, arrowtooth 

 flounder (Atheresthes stomias), rockfish [Sebastes spp.), 

 skates (Rajidae), squid, and octopus (Fig. 2, Table 2). 

 Species of salmon, rockfish, squids, and octopus could 

 be identified only to family, and other species, such as 

 Pacific herring or walleye pollock, could be identified 

 to species. Unfortunately not all recovered hard parts 

 could be identified to the species level. 



Steller sea lion diets at the Forrester Island rook- 

 eries were significantly different from one another in 

 1994 and 1998 (P<0.001), but the differences between 

 the diets at Forrester Island and those at Hazy Island 

 in 1993 and 1999 were not significant (P=0.06, 0.36, 

 respectively; Fig. 3). At White Sisters, mature females 

 consumed primarily forage fish followed by gadids; 

 whereas at Hazy Island, gadids were the dominant 

 prey. Further south at Forrester Island, the diet was 

 more evenly distributed between forage fish, salmon, 

 and gadids. Scats were collected in multiple years at 

 Forrester Island and Hazy Island and showed little dif- 

 ference in diet over time within each site (P=0.30, 0.11, 

 respectively). 



Outside of the breeding season, the diet of Steller sea 

 lions in Southeast Alaska was dominated by gadids (pri- 

 marily pollock; Figs, 4 and 5, Table 3). The abundance of 

 salmon in the diet dropped from summer to fall (Fig. 4, 

 Table 3) when the runs of salmon presumably passed 

 into the river systems. Forage fish were found in 37% of 

 the scats collected in the fall (Sep-Nov), in 43% of scats 

 in the winter, 47% in spring, and in 62% of scats in the 

 summer (Fig. 4). Squid and octopus were more important 

 in fall and winter (22% on average) than during summer. 

 Rockfish were consumed relatively frequently during the 

 summer but were largely absent in the diet from fall to 

 spring, presumably because they were not present or ac- 

 cessible in significant numbers. "Other" fishes (primarily 



Forrester 



Hazy 



White Sisters 



100 



50 





 100 



50- 





 100 



~ 50- 





 100 



50 





 100 



50 





 100 



60- 





 100 



1993 



1994 



1995 



1996 



1997 



1998 



1999 



FSGRFIOCH FSGRFIOCH FSGRFIOCH 



Figure 3 



Frequency of occurrence of prey types in Steller sea lion 

 (Eumetopias jubatiis'i scats by year from three Southeast 

 Alaskan rookeries (Forrester, Hazy, and White Sisters) in 

 summer I Jun-Augl. Types of prey consumed were F = forage 

 fish, S = salmon, G = gadids, R = rockfish, Fl = flatfish, 

 O = other, C = cephalopods, and H = hexagrammids. Data 

 were pooled across months. Sample sizes shown in each 

 panel indicate number of scats. 



skates, see Fig. 2) rose in importance from summer to 

 fall (13%; to 24%> respectively), peaking at 50%c in winter 

 (Fig. 4). Gadids, forage fishes, and other fishes were the 

 dominant prey during winter. In terms of diet diversity 

 (dd), Steller sea lions consumed the most diverse range 

 of prey categories during summer at rookeries (dd=5.34 

 on a scale of 1-8), and the least diverse during fall while 

 at haulouts (dd=3.53). 



Most scats contained at least two prey groups, and one 

 scat contained remains from all eight groups (Fig. 6). 

 The mean number of prey groups per scat ranged from 

 2.1 to 2.6 depending on season (Fig. 6). In general, the 

 distributions were skewed towards fewer prey groups 

 occurring together in a single scat in fall and spring, 

 and were more normally distributed in summer and 

 winter. The number of prey types per scat was not sig- 

 nificantly different between fall and spring or between 

 summer and winter (P>0.05; Tukey-Kramer test) but 

 did differ significantly between these seasonal pairings. 

 Those scats with only a single identifiable prey type 



