24 



NORTH AMERICAN FAUNA 68 



Scheffer (1955) concluded that a reduction in body size was 

 correlated with increasing population or crowding in the northern 

 fur seal ( Callorhinus ur sinus ) . The data presented below indicate 

 that adult sea otters from a crowded population weigh less than 

 animals from a sparse population. The length of adult otters from 

 sparse populations fell within the length range of otters from the 

 crowded Amchitka population (tables 2 and 3). However, an 

 insufficient number of animals from sparse populations were 

 available to demonstrate a statistically significant difference at the 

 conventional level of 0.05. 



Although few adult sea otter specimens (five males and four 

 females) are available from areas where sea otter populations are 

 sparse, the differences in body weight between these animals and 

 the Amchitka collection are noteworthy. Among 79 adult males 

 that were killed at Amchitka, the mean weight was 62.5 lb. (28.3 

 kg.), and the heaviest weighed 85 lb. (38.6 kg.). Among five that 

 were killed in sparsely populated areas, however, the mean weight 

 was 87.1 lb. (39.5 kg.) and the heaviest weighed 99 lb. (44.9 kg.). 

 The difference between the mean weights of these two samples is 

 24.6 lb. (11.2 kg.). This indicates that adult males in a sparse 

 population may average about 28 percent heavier than those in 

 crowded populations. The difference is significant at the 0.1 per- 

 cent level. The mean weight of four females from sparsely popu- 

 lated areas was about 16 percent greater than the mean weight 

 of 254 Amchitka females. When the animals were collected in 

 sparsely populated areas, no effort was made to select large 

 individuals. 



The lesser body weights of the Amchitka animals appear to 

 confirm conclusions drawn from food habits and mortality studies 

 that a large population there has created ecological conditions 

 which are below the optimum. Because the sample of adult otters 

 from sparsely populated areas is small, a more thorough statistical 

 evaluation of the apparent differences in mean body weight be- 

 tween crowded and sparse populations must be delayed until more 

 data are gathered. 



Most of the sea otters killed at Amchitka were taken during 

 the late winter to early spring period of environmental stress when 

 many of the otters were dying. Thus, it appears appropriate to 

 compare the animals killed at this season with others taken at 

 Amchitka in the fall when body condition would be expected to 

 be optimum. Unfortunately, the only fall (1962) sample of adults 

 is small, consisting of 3 males and 16 females. Comparison of the 

 mean weights of these animals with those taken in the late winter 



