Atlantic halibut is the largest flatfish species in the North Atlantic Ocean and supported a valuable commercial fishery in the U.S. until the 1840s. In the U.S., Atlantic halibut is considered a data-limited species and was listed as a “Species of Concern" by the National Marine Fisheries Service (NMFS) in 2004. In contrast, halibut abundance has steadily increased in Canadian waters over the last 20 years. Such a discrepancy in perceptions of abundance across the international boundary has drawn attention to the need for an improved understanding of halibut movements and stock structure.
Archival tags record and store environmental data including depth, temperature, light intensity, and acceleration. Pop-up satellite archival tags (PSATs) transmit recorded data via the Argos satellite system, meaning that data retrieval does not require fisheries recapture. Comparing these data with high-resolution oceanographic models permits estimation of daily positions while a tagged fish is at liberty using an algorithmic process called geolocation. However, unlike many other species, geolocation analyses of bottom-dwelling Atlantic halibut from PSAT data has been challenging, primarily due to a lack of reliable light signals at depth.
In this work, a hidden Markov model (HMM) geolocation method was developed to estimate the movement tracks of 25 tagged halibut based on the tag-recorded depth and temperature. Geolocation results indicated different movement patterns exhibited by the tagged halibut, including home range, return movement, and seasonal migration. Results also showed evidence of cross-jurisdictional migrations between U.S. and Canadian waters. Estimated movement tracks of some individuals also indicate overwintering behaviour that may identify putative spawning habitat where neither trawl surveys nor fishing occur. The HMM geolocation method serves as a useful tool for providing information on halibut movements to inform stock assessment and management decisions. This geolocation approach using PSAT data could be employed in other regions or with other species.
Read the full paper in ICES Journal of Marine Science.
Tagging an Atlantic halibut with PSAT. Photo: Crista Bank, Chang Liu
Authors: Chang Liu, Crista Bank, Michael Kersula, Geoffrey W Cowles, Douglas R Zemeckis, Steven X Cadrin, Christopher McGuire