shows the percent age composition of female 

 seals sampled from the kills on the Pribilof 

 Islands from 1958 to 1963. 



Reproduction 



The genital tracts of 3- and 4-year-old 

 females taken in the kill were classified in 

 the laboratory according to whether the female 

 had given birth to none, one, or two or more 

 pups in her lifetime. Presence of a placental 

 scar (site of umbilical cord attachment) in 

 one uterine horn confirmed birth of a pup in 

 1963. The fresh ovaries were examined for 

 Graafian follicles, then sectioned to detect 

 developing corpora lutea and to measure 

 follicles 5 mm. or larger in diameter. A 

 developing corpus luteum presumably indi- 

 cates that ovulation and conception have oc- 

 curred. Graafian follicles, if present, suggest 

 that the female is sexually mature and is 

 nearly ready to ovulate. According to Craig, 1 

 the ovaries of immature females "are struc- 

 tureless, containing no corpora lutea, corpora 

 albicantia, or Graafian follicles. A female 

 preparing to ovulate for the first time will 

 usually have equal numbers of follicles in each 

 ovary." Craig classifies the latter as "ma- 

 turing" females. Of "maturing" females, Craig 

 states that "Graafian follicles are first seen 

 in March, and increase in size and number 

 until the time of ovulation in late August or 

 early September, 1 to 2 months later than 

 subsequent ovulations." 



1 Allison M. Craig. 1963. Key to the reproductive con- 

 dition of female fur seals (Callorhinus ursinus) and the 

 reproductive cycle of mature female fur seals. Fisheries 

 Research Board of Canada, Biological Station, Nanaimo, 

 B.C. [Manuscript report.] 



The results of examining 310 pairs of 

 ovaries from known-age 3- and 4-year-old 

 females taken on St. Paul Island in 1963 are 

 summarized in table 9. Two of the 170 4-year- 

 old females were primiparous and had given 

 birth to their first pup in 1963; all (140) of 

 the 3-year-old females examined were nulli- 

 parous. 



Both ovaries of all but 3 of the 310 females 

 examined contained developing follicles or 

 follicles that were resorbing as a result of 

 ovulation. If the presence of follicles in both 

 ovaries usually results in ovulation the same 

 year, many of the 3- and 4-year-old females 

 either do not conceive or a large proportion 

 of the fetuses die early in life or both. For 

 example, of 295 5-year-old females examined 

 in 1962, 94 or 32 percent had given birth to 

 pups that year; only 13 or 3 percent of 398 

 4-year-old females had given birth. The dif- 

 ference between the observed pregnancy rates 

 of 4- and 5-year-old females examined in 

 1962 and the potential pregnancy rates of 3- 

 and 4-year-old females examined in 1963 may 

 also be influenced by unrepresentative sam- 

 pling and year to year variation in fecundity. 



The ovarian tissue of 3- and 4-year-old 

 females examined in 1963 differed in texture, 

 presumably as a result of hormones asso- 

 ciated with ovulation or conception. Ovaries 

 with developing corpora lutea were firm; 

 ovaries of females that had never ovulated 

 were soft and fragile. The ovaries of older 

 females are firm and, in addition, are laced 

 with connective tissue formed by corpora 

 albicantia. 



The reproductive conditions of Soviet- 

 tagged females taken in the kill on St. Paul 

 Island are given in table 10. 



Table 9. --Ovarian activity of 3- and 4-year-old female fur seals, St. Paul Island, 1963 



1 Evidence of ovulation based on a developing corpus luteum in one ovary. 



2 One or more Graafian follicles each 5 mm. or larger in diameter. Measurements were taken 

 after the ovaries were sectioned. 



3 Both ovaries with Graafian follicles, all less than 5 mm. in diameter. 



4 One or both ovaries without Graafian follicles. 



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