Movement and behaviour of Atlantic Halibut (Hippoglossus hippoglossus) in a juvenile hotspot detected by a passive moored acoustic receiver grid and active wave gliders

Novel acoustic receiver applications have recently enabled the monitoring of movements of migratory oceanic species. One such species is the Atlantic Halibut, a commercially important deep-water flatfish that exhibits complex migratory behaviours throughout the Northwest Atlantic Ocean. Here we set up a 144 km2 receiver grid (n = 24 VR4 receivers) in an important halibut hotspot on the Scotian Shelf and tagged 245 halibut with V13 and V16 tags from 2020–22. Receiver performance was assessed using a Receiver Efficiency Index, indicating that the deeper eastern side of the array was an area of high relative importance for future receiver deployments. Many halibut remained in consistent, localized areas over several years, occasionally making short movements into deeper water. We were also able to assess the post-release behaviour of four recaptured pre-tagged halibut within the grid array, indicating a brief period of hyperactivity and an eventual return to their previously observed behaviours. Wave gliders surveyed the grid site annually from 2021–23 to compare the efficacy of active tracking to stationary arrays for future halibut telemetry projects. Two of three tracking missions were disrupted by environmental disturbances, but results from the 2023 tracking mission indicated that the glider was able to detect more individual halibut than the stationary array in the same time frame. However, the short duration of the glider missions precluded their ability to identify movement and migratory patterns. Here we report lessons learned to streamline future project design for open ocean telemetry and halibut acoustic tracking.