Table 2. --Monthly records of age and sex of fur seals off California 



[Combined data for 1958, 1959, 1961, and 1964] 



1/ 



— Data for 1958, 1959, and 1961 are from North Pacific Fur Seal Commission Report on 

 Investigations from 1958 to 1961. 



and September were recorded. No mature 

 follicles, ruptured follicles, or forming corpora 

 lutea were noted in 2-year-old nulliparous 

 animals. In a sample of 27 3-year-olds, the 

 ovaries of 3 had either a ruptured follicle or 

 a developing corpus luteum; 4 had at least one 

 follicle greater than 5 mm. in diameter; and 

 the ovaries of 20 contained follicles less than 

 5 mm. in diameter. We judge, therefore, that 

 at least 3 and possibly 7 of the animals might 

 have given birth to pups at age 4. Only one 

 pregnant 4-year-old was collected. 



Pregnancy rate . --The pregnancy rate of 

 female seals collected in 1958-64 is shown 

 in table 4. The rate in 1964, by area and 

 month, and a comparison of these rates with 

 the combined data for 1958-63 are given in 

 appendix table 18. Several age classes of seals 

 collected off California--particularly 4, 5, and 

 6--had lower pregnancy rates than seals of the 

 same ages from other areas. A probable ex- 

 planation of the difference in rates is that 

 young nulliparous females and nonpregnant 

 older females linger at the southern end of 

 the migration range and fornn a greater pro- 

 portion of spring collections than of winter 

 collections. 



In Bering Sea nulliparous females of ages 

 1 to 6 made up about equal percentages (23.3 

 and 23.7) of the collections in 1963 and 1964. 

 In July, however, nulliparous females of these 

 ages composed 39 percent of the 1964 catch 

 as compared with 20 percent of the 1963 catch. 

 Pregnancy rates for ages 3 to 6 were 0, 2.7, 

 33.3, and 74.6 in 1964 and 0, 7.1, 43.8, and 

 74.4 in 1963. The pregnancy rate of 4-year- 

 old females varied in 1958-63 from a low of 



1.0 to a high of 7.1; the rate among 5-year-old 

 females varied from 20.6 to 56.1. These 

 variations, which apparently are the result of 

 sampling and distribution differences, are not 

 known to be important. 



The segregation of sexes demonstrated in 

 the 1964 collections calls attention again to 

 the problem of obtaining representative 

 samples for determining pregnancy rates used 

 in making population estinnates. Year-to-year 

 changes in rates can best be estimated from 

 samples taken in the same area at the same 

 time of year. Samples that vary in area and 

 date of collection in different years cannot 

 be compared safely. 



Uterine horn of pregnancy and fetal sex 

 ratio. - -Data collected since 1958 indicate that 

 pregnancies occur in the left uterine horn 

 more often than in the right. In 1964, 55 per- 

 cent of all pregnancies were in the left uterine 

 horn. In 1962, 1963, and 1964, 53, 51, and 53 

 percent of the primiparous animals carried a 

 pup in the left uterine horn in their first 

 pregnancy. 



Males and females were about equally 

 represented among fetuses in 1958-64. In 

 1964, 51 percent were male. 



Anomalies 



Gooseneck barnacles and algae ^ are fre- 

 quently attached and growing on the guard 

 hairs of fur seals . Barnacles and algae appeared 



5 Algae were identified by Ann Helander, and barnacles 

 by Dora P. Henry, Department of Oceanography, Uni- 

 versity of Washington, Seattle, Wash. 



