Research Document 2025/003

Data Inputs for the Assessment Framework Review of Atlantic Halibut on the Scotian Shelf and Southern Grand Banks in Northwest Atlantic Fisheries Organization Divisions 3NOPs4VWX5Zc

By Li, L., Hubley, B., Harper, D.L., Wilson, G., and den Heyer, C.E.

Abstract

Atlantic Halibut (Hippoglossus hippoglossus) is a large, sexually dimorphic flatfish and currently the most valuable groundfish fishery in Atlantic Canada. The Atlantic Halibut fishery was unregulated until 1988, at which time a total allowable catch was implemented for the Scotian Shelf and southern Grand Banks management unit (Northwest Atlantic Fisheries Organization [NAFO] Divisions 3NOPs4VWX5Zc). In 1994, a minimum legal size limit of 81 cm was adopted. Longline and otter trawl are the two major fishing gears used in this fishery. This paper is a review of the data inputs including biological parameters, ecosystem considerations, landings, indices of abundance, catch composition and mortality estimates used in fitting a statistical catch-at-length model. The length-weight relationship was updated using a new model and new data. Halibut abundance indices remain above long-term averages and the landings are among the highest on record. Rising ocean temperatures may have contributed to the increasing Halibut population since the early 2000s. Hundreds of Halibut stomachs collected in the Maritimes Summer Ecosystem Research Vessel (RV) Survey in NAFO Divisions 4VWX were analyzed and the occurrence rates of different prey were estimated. Halibut are landed with a number of other groundfish species including White Hake (Urophycis tenuis), Haddock (Melanogrammus aeglefinus), Pollock (Pollachius virens), and Atlantic Cod (Gadus morhua). Multiple indices of abundance have been estimated. The Maritimes Ecosystem RV surveys provide fisheries-independent indices of abundance of small Halibut. The Maritimes Summer Ecosystem RV Survey stratified mean number of Halibut per tow peaked in 2011, but remains well above the long-term mean. The stratified mean number of Halibut per tow from the Newfoundland and Labrador Spring Ecosystem RV Survey in 3NOPs has been generally increasing since early 2000s. In 1998, the Industry-DFO Halibut Longline Survey was established to provide an additional fishery-independent index of exploitable biomass throughout the management unit. A new Stratified Random Industry-DFO Halibut Longline Survey was introduced in 2017 and has been run concurrently with the Fixed Station Halibut Survey. The longline Halibut survey biomass index increased steadily since the mid-2000s, but in recent years has plateaued. An industry-DFO tagging program began in 2006. The multiyear mark-recapture model provides estimates of natural mortality (M) at 0.10 and fishing mortality (F) between 2007 and 2020. The peak estimated fishing mortality was 0.2 in 2008 and has since declined to between 0.03 and 0.04 since 2017. The data inputs will be used to fit an update of the statistical catch-at-length model previously accepted in 2014.

Research Document 2025/003 (PDF, 13,137 KB)

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