Table 20. — Tagged yearlings counted, by rookery, date, and sex, 

 St. Paul Island, 1963 



from birth to age 1. Only after the annual 

 counts are correlated with the return of the 

 same age classes at age 3 can the technique 

 be evaluated as an indicator of returns at 

 age 3. 



Appraisal of Problems Involved in Tagging 

 and Tag Recoveries 



Several factors that bias population esti- 

 mates were presented in the report for 1959. 6 

 Additional factors and the results of studying 

 these problems have been given in subsequent 

 reports T * and in Roppel, Johnson, Bauer, 

 Chapman, and Wilke (1963). 



Following is a summary of the factors 

 studied since 1959 and the changes made or 

 needed to improve the tagging and tag re- 

 covery program: 



Mortality differential between sexes . --Re- 

 liable information on differences in mortality 

 between males and females is difficult to 

 obtain. Because the heaviest mortality occurs 



«Carl E. Abegglen, Alton Y. Roppel, and Ford Wilke. 



1959. Alaska Fur Seal Investigations, Pribilof Islands, 

 Alaska, Report of field activities, June-September 1959. 

 Marine Mammal Biological Laboratory, Seattle, Wash. 

 [Manuscript report.] 



7 Carl E. Abegglen, Alton Y. Roppel, and Ford Wilke. 



1960. Alaska Fur Seal Investigations, Pribilof Islands, 

 Alaska, Report of field activities, June-October 1960. 

 Marine Mammal Biological Laboratory, Seattle, Wash. 

 [Manuscript report.] 



•Carl E. Abegglen, Alton Y. Roppel, Ancel M. Johnson, 

 and Ford Wilke. 1961. Fur Seal Investigations, Pribilof 

 Islands, Alaska, Report of field activities, June-November 



1961. Marine Mammal Biological Laboratory, Seattle, 

 Wash. [Manuscript report.] 



at sea and before age 3, the best source of 

 information on differential mortality should 

 be from the pelagic research kill. The data 

 collected to date, however, are inconclusive 

 because the number of 1- and 2 -year- old 

 seals taken at sea has been inadequate. 



Segregation by sex at the time of tagging . -- 

 An analysis of 8,522 tags recovered during 

 the years 1956-59 from E, F, G, H, and I 

 series showed that the sexes are not segre- 

 gated at the time of tagging. 



Effects of tagging. --Stress, physical injury 

 from handling and from tags and checkmarks, 

 and fatigue due to driving pups are possible 

 causes of extra mortality among tagged pups. 

 This extra mortality, however, is difficult 

 to assess because much of it may be delayed 

 until after the pups have gone to sea. 



From 1955 through 1962, about 30 men 

 tagged 50,000 to 60,000 pups each year. Be- 

 cause the rather high-speed operation caused 

 mortality and resulted in poor tag placement, 

 only 25,000 pups were tagged in 1963. Barri- 

 cades were used only on the larger rookeries. 

 Tables were not used at all, thereby avoiding 

 the need to drop or throw the pups after they 

 were tagged. Pups were driven very little. A 

 3- to 7-man crew tagged half (12,500) the 

 pups; 10,000 pups were tagged by 14 men and 

 2,500 were tagged by 10 men. These changes 

 probably improved tagging quality and 

 eliminated most of the immediate extra 

 mortality of tagged pups. 



Application of tags . --Prior to 1963, tag 

 placement ranged from very poor to excellent, 

 depending upon the skill of the person doing 

 the tagging and speed of the operation. To 

 avoid muscle and bone, tags should be attached 



19 



