230 



NORTH AMERICAN FAUNA 68 



It can thus be said that the female sea otter does not mature sex- 

 ually until after 2 years of age. 



The mean weight of 39 pregnant females was 50 lb. (22.7 kg.) 

 (extremes 36 and 70 lb.). Among 21 primiparous females, the mean 

 weight was 43 lb. (19.5 kg.) (extremes 35 and 52 lb.). If the 

 marked 33-lb., 2-year-old had continued to grow during her third 

 year at the rate she did in her second, her weight would have ap- 

 proximated the mean weight of the primiparous females. This 

 suggests that the female may become sexually mature at 3 years of 

 age. 



Among northern fur seals on the Pribilof Islands, the pregnancy 

 rate in 4-year-olds is about 3 percent and in 5-year-olds about 40 

 percent (Fiscus and Kajimura, 1967). If we assume a somewhat 

 similar condition in the sea otter, it is indicated that a small per- 

 centage of females may become pregnant after attaining 3 years of 

 age, i.e., in the fourth year, and that animals 5 or more years of age 

 constitute the important reproducing segment of the population 

 (see also 'Implication of Other Observations," p. 245-246). 



PREGNANT FEMALES 



Table 47 and figure 91 summarize data from 178 females show- 

 ing evidence of pregnancy. Among pregnant animals, unimplanted 

 pregnancy reached maximum frequency (100 percent) in the fall 

 sample. Implanted pregnancy increased in spring and reached 

 maximum frequency (69 percent) in summer. The high frequency 

 of large (weight class 5) fetuses in summer (50 percent, table 50) 

 and concurrent low frequency of unimplanted pregnancies (31 

 percent, table 47) indicate, as do the field counts of dependent 

 young, that parturition reaches a peak in summer. Although the 

 fall sample of tracts is small, it demonstrates that parturition in 

 the fall and winter accounts for a minority of births. 



Among 137 pregnant females from two samples for which data 

 are available (table 48), it is indicated that annually 17 percent 

 of the pregnant animals became pregnant for the first time and 

 that 83 percent are multiparous. 



Location of pregnancy 



A record of the uterine horn of pregnancy is available for 97 

 animals. Although the sample is small, it was gathered unselec- 

 tively and demonstrates that pregnancy occurs with equal fre- 

 quency in the right and left uterine horns (table 49). The location ■ 

 of implantation of the conceptus is usually within the center one- 

 third of the uterine horn. 



