Evaluation of age- and sex-dependent rates of tag loss in southern elephant seals

Rates of tag loss were estimated in a long-term tagging study of southern e lephant seals (Mirounga leonina) to assess the potential for bias in estima tes of survival rates. Dalton Jumbo Rototags(R) were applied to each hind f lipper of 5,743 recently weaned elephant seal pups on Marion Island from 19 83 to 1993. We adapted and developed a Method based on the resighting times of seals retaining 1 or 2 tags to estimate tag loss and test for effects o f age and sex of the seals. Tag loss by young seals was low but there was a strong increase in tag loss with seal age, especially for males. Annual si ngle tag loss at age 14 was 10% for males and 5.6% for females. Although th ese are relatively modest rates of tag loss, substantial fractions of seals (35% of males and 17% of females) would lose both tags by age 15, requirin g corrections to avoid bias in demographic studies based on these tagging d ata. The method we used to estimate tag loss has significant advantages ove r a ratio estimator that has been used for most previous studies of tag los s in pinnipeds.