Seasonal dispersion of Pacific halibut (Hippoglossus stenolepis) summering off British Columbia and the US Pacific Northwest evaluated via satellite archival tagging

Abstract

Fisheries for eastern Pacific halibut ( Hippoglossus stenolepis ) occur over a 9-month season that is closed in winter to protect spawners. The industry has requested season extension, but conventional tag data suggest that 67% of Canada’s fishable biomass may comprise Alaskan spawning stock vulnerable to out-of-area interception. Seventy-eight halibut were tagged during summer in Canada and the US Pacific Northwest (USPNW) with archival tags programmed to report via satellite on 1 February, 15 February, and 1 March. Fifty-seven tags (44 Canadian and 13 USPNW) escaped recapture and reported on or near their scheduled reporting dates. Only 7% out-of-area dispersion was observed for Canadian-tagged halibut; light-based geolocations suggested that an additional 4% may have emigrated prior to February and then returned. Halibut that emigrated were located north of their tagging location. From the USPNW, 46% dispersion was observed. Eighty-nine percent of the tagged halibut displayed depth profiles consistent with migration to offshore spawning areas during the winter, and the majority (78%) were located on the continental slope (>200 m) immediately prior to tag reporting, suggesting locations on or near spawning grounds. There was no detectable difference in dispersion by date, but the mean central position of Canadian-tagged halibut shifted progressively farther southeast over time.