TABLE 20. — Homing tendency of yearling 

 fur seals tagged as pups in 1961, 

 by rookery, St. Paul Island, 

 1962 



Rookery 



Percent 



Zapadni 



86 



Appraisal of Problems Involved in Tagging 

 and Tag Recoveries 



Several factors that bias population esti- 

 mates were presented in the report for 1959' 

 and evaluated in subsequent reports. ^ ' Changes 

 made or needed to improve the marking 

 techniques are given in the following discus- 

 sion: 



Quality of tags . — Style 19M tags furnished 

 by the manufacturer for put tagging in 1960, 

 1961, and 1962 were less than satisfactory. 

 Clinching failure was the primary problem. 

 Clinching failure was partially eliminated in 

 1962 by modifying the tagging pliers to fit 

 more precisely the contour of the tag. Be- 



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

 1959. Alaska Fur Seal Investigations, Pribilof Islands, 

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

 Bureau of Commercial Fisheries, Marine Mammal Re- 

 search, U.S. Fish and Wildlife Service, Seattle, Wash, 

 [Processed. ] 



''See footnote 1, p. 15. 



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

 andFordWilke. 1961. Fur Seal Investigations, Pribilof 

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

 ber 1961. Bureau of Commercial Fisheries, Marine 

 Mammal Biological Laboratory, U.S. Fish and Wildlife 

 Service, Seattle, Wash. [Processed. ] 



cause nearly 100 percent clinching success 

 was observed among the manufacturer's new 

 style 49M tags used on yearling seals in 1962, 

 this style will be used for pup tagging in 1963. 



Effects of tagging. — The mortality rate for 

 tagged pups was higher than that for untagged 

 pups during the period from 2 to 6 days after 

 tagging. Post-mortem examinations of 48 dead 

 tagged pups showed that 34 or 71 percent had 

 a heavy layer of blubber while 14 or 4 percent 

 had little or no blubber; 38 or 79 percent of 

 the dead tagged pups examined had cardiac 

 lesions indicative of acute congestive heart 

 failure. It follows that weight is a factor in 

 mortality of tagged pups. Over-exertion of 

 heavy pups as a result of their being forced 

 to travel some distance during the tagging 

 operation appears to produce heart failure. 

 Other possible causes of mortality of tagged 

 pups are gas gangrene from infected tag 

 wounds, skull fractures sustained during tag- 

 ging, and enteritis. The latter may be triggered 

 by the stress of tagging operations. 



In 1960, the effects of tagging on pup mor- 

 tality were studied,' and the effects were 

 measured by clearing the dead pups from the 

 areas just prior to tagging, then tagging pups 

 on the areas and periodically clearing the 

 rookeries of dead pups and recording the 

 number of tagged and untagged dead pups. 

 The rookeries were sampled to get an esti- 

 mate of the tag ratio among live pups but no 

 conclusions were made. The results from the 

 two areas were contradictory. 



A similar plan was followed during the 1962 

 field season; the data are given in table 21. 

 The data from 1962 show that tagged pups 

 have a higher mortality rate than untagged 

 pups the first week after tagging (x2 = 109.8, 

 P<.005). Counts made later than one week 

 after tagging also show that mortality of 

 tagged pups tends to be higher than that of 

 untagged pups, but the difference is not sig- 

 nificant. 



It was believed that there may be a general 

 increase in pup mortality on the rookeries 

 as a result of the disturbance from pup 



9 See footnote 1, page 15. 



30 



