Homing and summer feeding site fidelity of Pacific halibut (Hippoglossus stenolepis) in the Gulf of Alaska, established using satellite-transmitting archival tags

A total of 48 adult Pacific halibut were tagged in the Gulf of Alaska using Pop-up Archival Transmitting (PAT) tags. Fish were tagged during 2005 while on their summer feeding grounds and the tags programmed to release from their host fish (pop-up) exactly 365 days after deployment, thus providing a full year's environmental data (depth, temperature, and light levels) as well as each fish's location the summer after tagging. Nine tags were recovered by the commercial fleet substantially in advance of their pop-up dates, eight prematurely released from their host fish, and six failed to report to satellites on their programmed date. For halibut that escaped the fishery and whose tags broadcast reliable endpoint locations (n = 23) or were recaptured by the commercial fishery close to their pop-up date (n = 2), 80% were located within 20 km of their initial tagging location after 1 year at liberty. Depth records confirmed that most of these fish (n = 15; 60% of all tag recoveries) had actively homed to their summer grounds after spending winter in deep water at the shelf edge, as opposed to simply remaining near their tagging location throughout time at liberty. The rate of site fidelity observed here is further corroborated by an ongoing Passive Integrated Transponder (PIT) tagging study, suggesting that summer site fidelity and homing are likely to be general characteristics across recruited ages, as well as being interannually persistent. Homing provides a strong mechanism to establish and maintain population substructure, and high rates within a population have implications for ongoing research, interpretation of historical fishery trends, and conceptual models of population structure.