THE SEA OTTER IN THE EASTERN PACIFIC OCEAN 261 



strated when both sexes were held captive under the same con- 

 ditions. A similar situation was suggested in the northern fur 

 seal. Chapman (in Abegglen, Roppel, and Wilke, 1960) estimated 

 that in the first 3 years of life females outsurvived males by a 

 ratio of 2 to 1. Studies since then indicate that the ratio may be 

 only 1.25 to 1 in favor of females (Chapman, unpublished manu- 

 script). 



MORTALITY FACTORS 



Physical characteristics and food supply 



The terminal conditions observed in a high percentage of otters 

 found dead on Amchitka beaches are emaciation and hemorrhagic 

 enteritis. Enteritis may, however, occur in the final hours before 

 death after other conditions have doomed the animal. 



Sea otters found dead on beaches during the late-winter and 

 early-spring period of high mortality may be divided into two 

 primary groups: (1) Those whose death was apparently caused 

 by an injury in rough seas, or disease, and (2) those which showed 

 evidence of starvation and finally exhibited symptoms of enteritis. 

 Many dead animals cannot be placed positively into one group or 

 the other, ^-.n emaciated and weakened animal is more subject to 

 injury by large breakers than a strong one. An animal obviously 

 killed by an injury might have died soon of starvation. 



The actual cause of death of many animals cannot be determined 

 because of decomposition. Table 57 lists observed conditions which 

 may have caused death of otters that might be considered to be in 

 group (1) above. The section "Parasites and Miscellaneous Dis- 

 eases" gives additional data on mortality recorded by Dr. Robert L. 

 Rausch in 1952 and more detailed information on several speci- 

 mens that were examined in the laboratory. 



The dead animals which fall into the second group are of the 

 greatest interest from the point of view of population studies. 

 Most of these may be separated into two age groups : (1) Juveniles, 

 many of which approach subadulthood and, (2) old animals having 

 worn teeth and often showing other indications of advanced age, 

 such as gray pelage about the head, chest, and abdomen, and im- 

 paired vision caused by injuries or senile cataracts. In the 1959 

 study period a particular effort was made to record pertinent 

 data from 83 individual otters found dead on beaches. The infor- 

 mation is summarized in table 58. 



Juveniles and old adults had two characteristics in common at 

 death. Both lacked body fat and both showed a high incidence of 

 defective teeth. In the case of the young animals, 50 percent ex- 



