i 19 20 21 22 23 Z4 25 26 



AGE (YEARS) 



Figure 3.— Comparison of lengths by age of 4,074 pregnant, 

 2,353 nonpregnant, and 1,528 post partum female fur 

 seals collected by U.S. research vessels in eastern 

 Pacific. 1958-63. 



X= 1972 c? FETUSES 

 • = 2065 ? FETUSES 



NOV DEC JAN FEB MAR APR MAY JUN JUL AUG 



Figure 4. —Lengths of 4,037 fur seal fetuses plotted by 

 10-day periods, U.S. research vessel collections in 

 eastern Pacific, 1958-63. 



X = 1978 <f FETUSES 

 • = 2071 ? FETUSES 



FEB MAR APR MAY JUN JUL AUG 



Figure 5.~Weights of 4,049 fur seal fetuses plotted by 

 10-day periods, U.S. research vessel collections in 

 eastern Pacific, 1958-63. 



caption at age 4 in 1962. Of 92 4-year-old 

 nulliparous females, 25 had ovaries contain- 

 ing a ruptured follicle or a forming corpus 

 luteum. These results support conclusions 

 made previously that more females in the 

 Pribilof herd reached sexual maturity at age 

 4 than at any other age. The pregnancy rate 

 increases to 87.3-91.0 percent for the year 

 classes 8 through 13, and gradually declines 

 thereafter. 



The average pregnancy rate of 84.1 percent 

 for females 6 years and older is remarkably 

 uniform for the 6 collection years. The rate 

 decreased to 71.9 percent when 3-, 4-, and 

 5-year-old females are included. 



Reproductive conditions .- -The reproductive 

 conditions of females collected in the Bering 

 Sea are shown in table 7 by age and month, 



Nulliparous, primiparous, and multiparous 

 females were taken regularly throughout the 

 season and uniformly over the collection area. 

 A ruptured follicle or a developing corpus 

 luteum was observed in the ovaries of 6 of 36 

 3-year-old nulliparous females collected. Five 

 primiparous and three multiparous 4-year- 

 olds were the youngest pregnant females 

 taken. The latter three had apparently reached 

 some stage of pregnancy at age 3. 



Nonpregnant, multiparous females iwere col- 

 lected consistently through July ajid August. 

 The majority of them were 12 years old or 

 older. The pattern of sexual maturity and 

 pregnancy rates shown by data collected in 



