Tntes et al : Diets of Eumetopias jubatus in Southeast Alaska 



241 



Table 3 



Split-sample frequency of occurrence of prey types in Steller sea lion {Eumetopias jubatus) scats from Southeast Alaska. Samples 

 were from rookeries (Forrester, Hazy, and White Sisters) in summer (Jun-Augl 1993-99 and from haulouts in fall (Sep-Nov) 

 1993 and 1995-96, winter (Dec-Feb) 1996-1997, and spring (Mar-May) 1996. The rookery data (summer) were pooled across 

 months (and sites within the Forrester complex) but averaged across years and rookeries (weighted by pup counts). Haulout data 

 were pooled across months and sites, but were averaged across years. 



Prey category {%) 



Season 



Cephalopods Flatfish Forage fish Gadids Hexagrammids Other Rockfish Salmon 



Winter (Dec-Feb) 8.1 



Spring (Mar-May) 5.0 



Summer (Jun-Aug) 0.8 



Fall (Sep-Nov) 7.0 



7.6 

 7.6 

 6.4 

 6.2 



13.5 

 21.0 

 21.9 

 12.5 



49.1 

 52.5 

 27.3 

 62.2 



0.0 

 0.0 

 0.4 

 0.1 



from rookeries (r=-0.16) and with forage fish from scats 

 collected at haulouts (r=-0.10). 



Plotting our estimate of dietary diversity for Southeast 

 Alaska during summer with values recalculated for oth- 

 er regions of Alaska revealed a significant relationship 

 between diet diversity and the rate of population change 

 during 1990-94 (Fig. 9). High rates of population decline 

 correlated with low levels of diet diversity. 



Discussion 



The Southeast Alaska population of Steller sea lions 

 grew considerably since the first census of 100 animals 

 was made at Forrester Island in the 1920s (Rowley, 



1929). Subsequent counts were 350 sea lions (nonpups) 

 in 1945 (Imler and Sarber, 1947), and 2500 in 1957 

 (Mathisen and Lopp, 1963). The total population in 1992 

 (including pups) was estimated at 10,003 (Trites and 

 Larkin, 1996), and an annual growth rate of 6% was 

 estimated (1979-97; Calkins et al., 1999). Steller sea 

 lions were first noted breeding on White Sisters (3 pups) 

 and Hazy Island (30 pups born) in 1979. In 1997, 205 

 pups were counted at White Sisters, 1157 were counted 

 at Hazy, and 2798 were counted at Forrester Island. 

 Small numbers of pups have since been noted at Graves 

 Rocks and Biali Rocks (Pitcher et al., 2007). 



It is not clear why Steller sea lion populations grew 

 through the 20'^' century in Southeast Alaska. One 

 possible explanation is that predation by killer whales 



