Stock-scale electronic tracking of Atlantic halibut reveals summer site fidelity and winter mixing on common spawning grounds

Knowledge of movement ecology, habitat use, and spatiotemporal distribution is critical to inform sustainable fisheries management and conservation. Atlantic halibut in the Gulf of St. Lawrence (GSL) is of great economic value, although little is known about its spatiotemporal distribution, seasonal migrations, and spawning areas. To investigate these aspects, 114 pop-up satellite archival tags (PSATs) were deployed on halibut from 2013 up to 2018 throughout the GSL. A total of 62 physically recovered PSATs provided complete archived datasets with high temporal resolution. PSAT detachment locations revealed specific summer site fidelity. In contrast, the reconstruction of movement tracks with a geolocation model revealed that all fish converged to the Gulf’s deep channels to overwinter and spawn. This suggests strong mixing during the spawning period and thus one reproductive population within the GSL. These findings illustrate the utility of large-scale PSAT tagging combined with dedicated PSAT-recovery surveys to reveal critical stock-scale information on movements and spawning locations. This information addresses important gaps in the movement ecology of this halibut stock, revealing that reported summer site fidelity, based on years of conventional tagging, also conceals important winter mixing that is only apparent through analyses of movement on the time scale of annual cycles.