Tag-shedding from South African fur seals Arctocephalus pusillus pusillus

Abstract

Rates of tag-shedding are determined for monel-metal tags applied to fore-flippers of 21 799 pups of the South African fur seal Arctocephalus pusillus pusillus in 12 colonies in the years 1971 and 1973–1979. Half of the pups (alternate ones) were tagged on both fore-flippers. The major aim of the study was to estimate pup population size by mark-recapture. Collection of tags from pups killed in harvests 5–9 months after tagging permitted rates of tag-shedding to be determined. For 10 different taggers, this averaged 0, 149 (SE 0, 0053), and ranged from 0, 068 to 0, 338 for individual taggers. Because it is easier to apply a tag to one fore-flipper than the other, the rates of tag-shedding are likely to be inflated over what they would be if all pups were given a single tag applied to the flipper of choice. The variation between taggers indicates that greater efforts should be made to standardize tagging procedures. The average rate of tag-shedding was similar to that reported for Weddell seals Leptonychotes weddellii in their first year and for young northern fur seals Callorhinus ursinus (although age-classes and time periods for the latter species were different). The high rate of tag-shedding within the first year of life highlights the need to include this parameter when estimating survival rates based on tagged animals. © 1994 Taylor & Francis Group, LLC.