THE SEA OTTER IN THE EASTERN PACIFIC OCEAN 241 



by young do not enter estrus. (2) Even if the pup is lost, estrus 

 may be delayed until after evidence of parturition (lactation, pla- 

 cental scar, or corpora albicantia) has disappeared or nearly 

 disappeared. (3) In fall there is a maximum number of nonpreg- 

 nant animals in the population, since many females are accom- 

 panied by young born in spring and summer. (4) Because the 

 percentage of proestrous and estrous animals in the nonpregnant 

 population is small, it is indicated that impregnation takes place 

 soon after the onset of follicular activity. 



With the probability of a sampling bias toward a high frequency 

 of pregnant animals in mind, it may be considered that more than 

 one-third and probably at least half of the sexually mature female 

 population is always nonpregnant (fig. 91). This coincides with 

 general observations that the mother sea otter cares for her pup 

 for about a year. When she separates from her young, she may 

 become pregnant and give birth again about 2 years after the 

 prior parturition (see analysis by Chapman that follows). 



The period between normal separation of the mother from the 

 young and the onset of estrus is unknown. If this period is long, 

 the period between births may be longer than 2 years. That the 

 period between separation from the young and the onset of estrus 

 may be extended is indicated by the observation that ovaries were 

 inactive in females which were multiparous but not lactating or 

 accompanied by a pup and showed questionable evidence (indistinct 

 recent corpus albicantia tissue and slight uterine discoloration) 

 of having been post partum for a long time. 



Rate of reproduction 



The counts recorded in table 52 were made in an area favored 

 by females (see Segregation of Sexes). Data obtained from ani- 

 mals killed in the Constantine Harbor to the Kirilof Bay areas 

 reveal that among 91 animals 19 (21 percent) were males (Segre- 

 gation of Sexes, table 43). 



It was shown that for general purposes the sea otter sex ratio 

 may be considered 50:50 (see Sex Ratio). If 21 percent of the 

 animals in the field counts were males (from table 52: 2,114 X 

 0.21 = 444 males, 2,114 — 444 = 1,670 females; males and females 

 in total population = 1,670 X 2 = 3,340 independent male and 

 female ; 



3,340 + 537 young = 3,877; ^^\^rj^^^ = 14 percent, i.e., young 



to independent animals 14 percent dependent young) then the 

 mean annual percent of young in the entire population is 14 



