THE SEA OTTER IN THE EASTERN PACIFIC OCEAN 247 



10. Caudal and cephalic presentation of the fetus occurs with 

 about equal frequency. 



11. Twinning is possible but rare, and if twins are bom there 

 is no evidence to show that both survive. 



12. Females accompanied by young or showing positive evi- 

 dence of parturition do not normally enter estrus. 



13. Low frequency of estrous and proestrous females among 

 nonpregnant females at all seasons indicate that impregnation 

 occurs soon after the onset of follicular activity. 



14. Annually 17 percent of the pregnant animals are pregnant 

 for the first time and 83 percent are muciparous. 



15. Pregnancy occurs with equal frequency in each uterine 

 horn. 



16. The annual rate of reproduction in the total population is 

 estimated to be about 14 to 15 percent (i.e., about 16 young born 

 per 100 independent animals of both sexes and all ages). 



17. It is estimated that the female sea otter reaches sexual 

 maturity at age 4 years (3 years after becoming independent). 



Reproduction in the Male 



Observations of courtship behavior in all seasons and the occur- 

 rence of newborn young in all months indicate that male sea otters 

 may be sexually active at any season. 



A preliminary histological study of testes was made of 40 sea 

 otters taken in the January to April period in 1958, 1959, and 1962. 

 These specimens indicate that spermatozoa are produced when 

 the testes attain a weight of about 13 to 14 g. Spermatozoa are 

 probably not produced by animals having a body weight of less 

 than 50 lb., but most of those weighing 55 lb. and all of those 

 weighing 60 lb. or over may produce spermatozoa. 



Dr. Edward C. Roosen-Runge, Department of Biological Struc- 

 ture, University of Washington Medical School, Seattle, kindly 

 examined the histological specimens of sea otter testes and con- 

 tributed the following information concerning the adult: 



No quantitative evaluation was attempted. Spermatogenesis was evaluated 

 by the stages of germ cells present. The last stage of spermatogenesis is that 

 in which the late spermatids (with dense and elongate heads) are lining the 

 lumen of the tubule. If an appreciable number of tubular sections were found 

 containing this stage or stages immediately preceding it, it was assumed that 

 many spermatozoa were liberated at this time from this testis. If many stages 

 of spermatogenesis were found, but few of the very late ones, it was assumed 

 that there was a slowing down or a standstill somewhere in the development 

 of germ cells or that some periodicity occurred in the liberation of sperm. 



