Retention of Anchor and Passive Integrated Transponder Tags by Arctic Grayling

Abstract

Double-tagging experiments provide the necessary information to evaluate the relative merits of different tag types, as well as information for the correction of population dynamics parameters such as population estimates and survival. We initiated a double-tagging experiment in 1993 to evaluate the relative merits of passive integrated transponder (PIT) and anchor tags for tagging Arctic grayling Thymallus arcticus. Tag retention was best represented by power curves for both tag types. Instantaneous losses were higher for PIT tags (7% and 14%, respectively, for anchor and PIT tags). Despite this initial disparity, tag retention was very similar between the two tag types after 3 years (85% and 83%, respectively, for anchor and PIT tags). Loss of anchor tags accelerated over time while loss of PIT tags remained reasonably constant. We estimated that half the anchor tags would be lost within 6 years and that all would be lost within 8 years. In contrast, it would take 11 years for half the PIT tags to be lost and 17 years for all PIT tags to be lost. This may be an underestimate of PIT-tag retention, and PIT tags not lost initially may be retained for the life of the fish.