REPRODUCTION 



Sex Ratio 



Because sea otters segregate themselves according to sex, the 

 raw data from samples killed, captured, or found dead on beaches 

 at Amchitka Island must be carefully evaluated before drav^ing 

 any conclusions concerning the sex ratio among different age 

 classes. 



PRENATAL SEX RATIO 



Three samples of fetal sea otters are available from females 

 killed in 1962 and 1963. The data are summarized in table 41. The 

 smallest fetus in v^hich sex w^as positively determined v^eighed 

 8.80 g. Among the 58 fetuses in which sex was determined, the 

 ratio was 45 percent males : 55 percent females. The fact that the 

 two 1963 samples show a nearly 50 : 50 ratio indicates that until a 

 larger sample is available the prenatal sex ratio may, for practical 

 purposes, be considered to be about 1 : 1. 



JUVENILE SEX RATIO 



Data on the sex ratio of juvenile otters were gathered during 

 tagging studies when sea otters were netted, tagged, and released. 

 This work was done mostly before the period in which high 

 mortality occurred. The young otters were in the areas frequented 

 primarily by females with young. Many of the young that were 

 captured for marking were still in company of their mothers or 

 recently separated from them. Mortality among young in company 

 with their mothers is not knov^ but apparently is low or moderate. 



Table 41. — Prenatal sex ratio at Amchitka Island 



Number Ratio (percent) 



Date taken 



Males 



Females 



Total 



Males 



Females 



22 Jan .-9 Mar. 1962- 



4 



9 



13 



31 



69 



17-31 Mar. 1963 



18 



19 



37 



49 



51 



31 July-3 Aug. 1963 



4 



4 



8 



50 



50 



Total .... 



26 



32 



58 



45 



55 



206 



