Ocean mortality, which accounts for the re- 

 maining three-quarters, can be measured 

 only by the return of survivors to the com- 

 mercial kill. It is now believed that each age 

 class suffers its heaviest mortality during 

 its first winter at sea. 



An understanding of mortality factors and 

 a means of measuring their influence on sur- 

 vival of the year classes are needed for 

 making accurate kill forecasts. The approaches 

 to parts of this problem that have been tried 

 are given in other parts of the report. 



Mark C. Keyes, a veterinarian, joined the 

 staff of the Marine Mammal Biological Lab- 

 oratory on 9 July 1962 to study mortality 

 causes in fur seals. He was on St. Paul 

 Island from 15 August to 10 September to (1) 

 become familiar with fur seal management 

 practices and their relation to mortality stud- 

 ies, (2) survey existing laboratory facilities 

 on St. Paul Island and determine what modi- 

 fications and supplies would be needed for con- 

 tinued research on mortality, (3) make post- 

 mortem examinations of recently dead or 

 moribund seal pups, (4) evaluate the influence 

 of tagging practices on pup mortality, (5) collect 

 specimen material from seals for histopath- 

 ologic study, and (6) become familiar with 

 hookworm biology investigations being carried 

 on by O. W. Olsen and E.T.Lyons of Colorado 

 State University. Some preliminary results 

 of work done in 1962 are given below and on 

 page 53. A detailed report on the results of 

 post-mortem examinations and on tagging 

 practices is on file at the Bureau of Com- 

 mercial Fisheries Marine Mammal Biological 

 Laboratory, Seattle. 



Post-mortem examinations of fur seal pups 

 were made from 15 August to 10 September 

 1962. During this period, pup mortality was 

 relatively light. Starvation was the primary 

 cause of death and enteritis, pneumonia, and 

 pediculosis were considered secondary causes. 

 Hookworm infestations had declined sharply 

 and could not be considered a significant 

 mortality factor. 



Gross and microscopic examination of the 

 intestinal contents of a seal pup on St. Paul 

 Island and culture studies of a captive fur 



seal in Seattle, Wash., indicate that the bac- 

 terium Clostridum perfringens is a likely agent 

 of enteritis among fur seal pups. 



Pneumonia in pups was characterized by 

 mild inflammation, congestion and atelectasis 

 of the lungs, suggesting a virus as the etio- 

 logical agent. A virus may also be responsible 

 for the prevalence of excessive ophthalmic 

 exudate among fur seal pups. 



Pediculosis is widespread among fur seal 

 pups on the rookeries. Because of their ability 

 to cause anemia and transmit disease, lice 

 may be an important factor in mortality. 



Dead-pup Counts 



Total counts . — Pup mortality in 1962 de- 

 creased by 22 percent of the 1961 count on 

 St. Paul Island and by 39 percent on St. 

 George Island. Counts for both islands are 

 given by rookery in table 26. Dead-pup counts 

 made since 1940 are presented in appendix 

 table 31. 



Although records are kept of tagged pups 

 found dead on Pacific coast beaches (table 27), 

 the data are incomplete and are not usable for 

 estimating ocean mortality. 



Counts on sample areas . — Counts on the 

 sample areas were contained in 1962 as a 

 part of the annual dead-pup count (tables 28 

 and 29). 



Comparison of total dead-pup counts with 

 counts from sample areas, St. Paul Island.-- 

 The data from 1956 to 1962 were analyzed to 

 determine how accurately the total number of 

 dead pups can be estimated from the count 

 on the sample areas. Two methods were used: 

 The first was based on the ratio of counts 

 from the- sample areas to the total count de- 

 termined from the 7 years of data; the second 

 was based on a regression equation. Table 30 

 shows that differences between the estimates 

 for each year and the actual counts are gen- 

 erally less than 5 percent of the latter. The 

 95 percent confidence limits for either of the 

 estimates are + 7,000 or less. Confidence 

 limits of estimates based on the regression 

 equation are generally less than those for 



36 



