Electronic tags reveal high migratory diversity within the largest Atlantic halibut (Hippoglossus hippoglossus) stock

Abstract

Growing evidence suggests that complex spatial structure occurs within the Scotian Shelf and southern Grand Banks (SSGB) Atlantic halibut stock, yet large knowledge gaps remain about diversity of migratory and spawning behaviors. Here, 71 pop-up satellite archival tags were deployed on large Atlantic halibut (FL: 87–166 cm) between 2012 and 2020. Migration tracks were successfully reconstructed for 43 fish using a hidden Markov geolocation model, and temperature and depth time series were available for an additional nine fish (total n = 52). Five migratory behavior categories were identified: shelf residency, slope residency, shelf-channel migration, shelf-slope migration, and dispersal. High-resolution data for four of 20 physically recovered tags provided evidence of putative spawning behavior in deep channels on the continental shelf and along the continental slope between January and February. Additionally, four halibut displayed previously undocumented periods of sustained, oscillatory vertical movements along the continental slope between November and February. The high migratory diversity observed in this study provides support for the existence of multiple resident and migratory contingents in the SSGB stock in the apparent absence of significant genetic structure.