NOTE Merrick et al.: Eumetopias jubatus pup masses 



755 



Table 1 



Steller sea lion, Eumetopias jubatus, mean pup masses (kg) by date, sex, and rookery, collected during 1987-94. n indicates 

 number of pups weighed, and SD indicates standard deviation of the mean value. T-value represents the Student's t calculated for 

 the comparison of male and female masses for the site and year combination. All <-tests were significant at P<0.01. 



Site 



Weighing date 



Oregon 



Rogue Reef 



30Jun 1987 



29Jun 1888 



7 Jul 1990 



SE Alaska (Forrester Island Complex) 



North Rock 28 Jun 1990 



Cape Horn Rock 

 and Lowrie 29 Jun 1990 



56 

 46 

 20 



56 

 64 



23 

 89 

 29 

 19 

 27 

 24 



28 

 25 

 15 

 20 

 23 

 27 

 25 



Female mass 



Male mass 



Mean (kg) 



SD 



Mean (kg) SD f-value 



Alaska Department of Fish and Game (ADF&G 5 ) in 

 1965 and 1975 (Table 2; ADF&G). To our knowledge, 

 these are the only data on pup size that have been 

 collected prior to our study. 



Variation in mean pup mass within the 26 June- 

 8 July weighing period was analyzed for Oregon, the 

 Gulf of Alaska, and the Aleutian Islands by using a 

 linear regression of the natural log of mean mass 

 from a weighing against weighing day. Significance 

 and equality of slopes of the regressions were tested 

 with a Student's ^-statistic. 



Mean pup masses collected for the 26-30 June 

 period were compared for the Oregon, Southeast 

 Alaska, and Gulf of Alaska regions by using Student's 

 ^-statistic. Means and standard errors were calcu- 

 lated for each area's weighings by treating each 

 weighing as a separate strata; calculations were per- 

 formed by methods of stratified random sampling 



5 Alaska Department of Fish and Game, 333 Raspberry Road, 

 Anchorage, AK 99518. Unpubl. data, 1976. 



(Cochran, 1977). Mean pup masses obtained from the 

 Gulf of Alaska and Aleutian Islands were compared 

 by using an analysis of covariance (with weighing 

 day as the covariate) because of the 14-day spread 

 in weighing days at these locations. Note that to use 

 an analysis of covariance, the slopes of the regres- 

 sion of mass against weighing date were first com- 

 pared for the Gulf of Alaska and Aleutian Islands to 

 ensure homogeneity of slopes. 



Results 



Male pups ( x =30.5 kg, standard error [SE]=0.3) were 

 significantly heavier (£=318.8, P<0.01) than female 

 pups ( £=26.2 kg, SE=0.212) for all sites combined. 

 Males were also significantly heavier at all individual 

 rookeries in all years sampled (Table 1; P<0.01). 



The only significant interannual variation in mean 

 pup masses for 1987-94 was for female pups at 

 Ugamak Island (F-4. 15, P=0.04). No significant inter- 



