Douglas Peterson, Ronald Twibell, Mattew Piteo

U.S. Fish and Wildlife Service, 1440 Abernathy Creek Rd, Longview, WA 98632

A fundamental assumption of mark-recapture studies is that individuals do not lose their marks or tags, because tag loss can lead to biased parameter estimates. Retention of 8-mm full-duplex and 12-mm half-duplex passive integrated transponder (PIT) tags implanted in the abdomen, opercular musculature, and dorsal sinus of age-0+ hatchery male brook trout (Salvelinus fontinalis) was evaluated in the laboratory. Treatments included single- and double-tagged fish. Survival, growth, and tag retention were monitored for 181–187 days for 640 tagged fish and 80 untagged controls. Survival to 180 days ranged 95%–100% and was not affected by tagging. PIT-tagging caused a short-term reduction in growth rates. Tag retention to 180 days was 100% for dorsal implantation, 83.0% with 8-mm tags in the operculum, 97.5% with 8-mm tags in the abdomen, and 99.6% with 12-mm tags in the abdomen. Retention of opercular tags was positively related to size at tagging. Tag loss was independent of whether fish were single- or double-tagged. Double tagging with one full- and one half-duplex PIT tag in different body locations would hedge against data loss relative to single tagging, especially for longer-lived and iteroparous species where tag loss through time is more likely.