Background: Passive integrated transponder (PIT) tags have been used to document and monitor the movement, behavior, or survival of numerous species of fishes. Data on short-and long-term survival and tag retention are needed before initiating studies using PIT tags on a new species or life stage. We evaluated the survival and tag retention of 153 metamorphosing juvenile sea lamprey Petromyzon marinus tagged with 12-mm PIT tags on three occasions using a simple surgical procedure. Results:Tag retention was 100 and 98.6% at 24 h and 28-105 days post-tagging. Of the lamprey that retained their tags, 87.3% had incisions sufficiently healed to prevent further loss. Survival was 100 and 92.7% at 24 h and 41-118 day post-tagging with no significant difference in survival between tagged and untagged control lamprey. Of the 11 lamprey that died, four had symptoms that indicated their death was directly related to tagging. Survival was positively correlated with sea lamprey length. Conclusions:Given the overall high level of survival and tag retention in this study, future studies can utilize 12-mm PIT tags to monitor metamorphosing juvenile sea lamprey movement and migration patterns.

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Lake trout (Salvelinus namaycush) were discovered in Yellowstone Lake in 1994 and their population expanded dramatically despite intensive suppression. The lake is species-depauperate, with no major lake trout embryo predators. We hypothesized that without this predation threat, lake trout free embryo feeding and growth may be greater than in their native range, leading to increased survival of age-0 individuals and rapid population growth. We compared length, developmental rate, and feeding patterns of lake trout free embryos captured at a spawning site in Yellowstone Lake with free embryos captured in their native range in Lake Champlain, Vermont. More embryos were feeding, contained more food, and were significantly longer at the same developmental stages in Yellowstone Lake. With an abundance of available food and minimal threat of predation, free embryos remained on the spawning site in Yellowstone Lake later into the summer than in Lake Champlain and achieved a greater maximum length before they dispersed. Greater food consumption and associated growth likely leads to high survival of lake trout free embryos in Yellowstone Lake, contributing to rapid population growth.