tags were attached to each of 686 males 

 (table A-Z8) considered to be yearlings on the 

 basis of body lengths, and to 28 known year- 

 lings that had been marked as pups in 1967 

 and given one lU-series tag (table A-29). 

 Fourteen of the latter were born on islands 

 owned by the U.S.S.R. Each tag was attached 

 to a front flipper at the hairline (fig. 9). The 

 mean body length (tip of nose to tip of tail) of 

 all aninnals tagged was 93.4 cm. 



Male Seals Age 2 Years 



A total of 1,495 males known or believed to 

 be 2 years old were marked with 2U-series 

 tags. Soviet biologists had attached tags to 3 

 of these animals as pups in 1966, United States 

 biologists had marked 29 with tags as pups 

 and 54 by removing parts of flippers in 1966, 

 and 1,409 had never been marked. All seals 

 without tags were given two tags, and those 

 with one tag were given an additional one. 

 Each tag was attached to the front flipper at 

 the hairline (fig. 9). We will determine the 

 age of these seals at the time of tagging from 

 their canine teeth when they are killed on the 

 Pribilof Islands or elsewhere. In the past, 

 some seals judged to be 2 years old were 

 ages 1, 3, and 4. 



Tables A-30 and A-31 give the number of 

 seals tagged at "age 2" in 1968. 



RECOVERIES OF MARKED SEALS 



Data on marked animals recovered in 1968, 

 an analysis of tag loss, the effect of the time of 

 marking on survival, and the value of tags 

 versus other marks are included in this section. 



Marked Seals 



Seals marked on the Pribilof Islands in 

 previous years and recovered there in 1968 

 included 3,907 that had been given single tags 

 or other marks as pups (table A-32) and 1,197 

 that had been given double tags at age 1 or 

 older (table A-33). The information is in- 

 complete for 228 of the aninaals that had been 

 tagged at age 1 or older; the age of 40 could 

 not be determined because the heads or 

 flippers were separated from the carcasses 

 during the skinning process, and 188 had lost 

 both tags. 



Marked seals killed from 26 June to 2 August 

 were tabulated separately from those killed 

 3-16 August (table A-32) because the ages of 

 1,333 males taken during the latter period 

 were not determined. In some of the analyses 

 elsewhere in this report we use the data for 

 these two periods separately. 



Table A-34 and A-35 give the rookery of 

 marking and location of recovery for seals 

 given tags and checkmarks as pups in pre- 

 vious years and killed in 1968. 



Thirty-nine seals tagged as pups by the 

 Soviets were killed on the Pribilof Islands in 

 1968 (table A-36). 



Tag Loss 



Seals tagged as pups are also given a check- 

 mark (fig. 9) so that the rate of tag loss can 

 be determined. Rates of tag loss among males 

 in ages 3, 4, and 5 are not greatly different 

 from those among females of the same ages, 

 though the comparison is based on a large kill 

 of males of these ages and a relatively low 

 kill of females. Females 4 years apart in age 

 have the same identifying mark and cannot be 

 accurately identified as to the year of birth 

 if age 6 or older. We cannot, therefore, 

 calculate a rate of tag loss for older females. 



Table 14 shows the rates of tag loss among 

 males tagged as pups with O- through S-series 

 tags. The loss observed among males killed 

 on St. George Island was les's than that for 

 males killed on St. Paul Island for all series, 

 possibly because marked seals were over- 

 looked when the carcasses were examined 

 on the kill fields of St. George Island. On 

 St. Paul Island, the carcasses are examined 

 for tags and marks in the mink-food process- 

 ing plant. 



Seals tagged at age 1 or older are given two 

 tags but no checkmark. The incidence of tag 

 loss among these animals has been similar 

 to that among seals tagged as pups, with the 

 exception of IT- and 2T-series tags attached 

 to seals in 1967. For no apparent reason, the 

 rate of loss for these tags was only about 

 one -tenth that observed for tags of other series 

 (table 15). Seals killed in the future willbe ex- 

 amined carefully to determine what caused the 

 low rate of loss for IT- and 2T-series tags 

 or whether the rate of loss is real. 



If its rate is constant, tag loss should in- 

 crease as the interval between tagging and 

 recovery lengthens; however, we observed only 

 slight increases for seals tagged as pups and 

 at age I or older. Apparently, tag loss is 

 highest soon after tagging and the probability 

 of loss becomes less thereafter. 



Time of Tagging 



For many years, pups were tagged on the 

 Pribilof Islands during the latter half of August, 

 when they were about 2 months old and rel- 

 atively small. We began to suspect, however, 

 that the survival of tagged pups would be greater 

 if they were tagged later in the season than 

 August. Therefore, in 1963 we began a test of 

 age at tagging as a factor in the survival of 

 tagged pups. 



Half of the pups tagged on St. Paul Island in 

 1963 and in 1964 were tagged in mid-August, 

 and half were tagged in late September. The 

 recovery rate has been significantly higher 



14 



