Science Advisory Report 2009/023

Stock Assessment of Atlantic halibut of the Gulf of St. Lawrence (divisions 4RST) in 2008

Summary

• Preliminary landings declared for the May 15 to December 31, 2008 period totalled 514 tons, which was 8% more than the TAC (475 t) for the 2008-2009 fishing season. These landings represent the highest recorded quantity since the end of the 1960s.
• A fifth (111 t) of the 2008 Atlantic halibut landings were by-catches from the gillnet fishery. Of these 111 t, 80% were associated to the Greenland halibut directed fishery. Observers’ data indicate that most of the catches (86% in numbers) during this fishery were made up of individuals whose sizes were under the minimum legal size of 81 cm. This portion of catches is not landed and must be discarded at sea according to the applicable regulations for the species.
• During the 2000s, abundance and biomass indices from scientific trawl surveys showed a considerable increase in the Gulf, and culminated in 2007. The 2008 index values remained among the highest of the series. The range of sizes recorded in the catches is large. The mean size varies between 60 and 70 cm in the Northern Gulf and is smaller in the Southern Gulf.
• Catches per unit effort recorded for the directed halibut longline fishery have been increasing steadily since 2000. This increase has been more noticeable over the last four years. Longline catches recorded at sea showed a significant presence of halibut measuring <81 cm (40% in numbers).
• A study revealed that 50% of females from the Gulf stock reach sexual maturity at 130 cm. Thus, modal size, recorded at sea from fixed gear halibut catches and from landings, averaged around 81 cm, which equals the minimum legal size. Therefore, it is likely that the females caught are almost all sexually immature.
• Any fishery management measure should be aimed at reducing Atlantic halibut catches of less than 81 cm, particularly in the case of the gillnet fishery where the fish mortality rate is very high.
• Over the last four years, halibut catches have increased far more rapidly that the TAC, due to the fact that the TAC was exceeded, but mostly because of the increasing number of fish under the legal size being discarded, mostly in gillnets where survival is presumably almost nil. In such conditions, it is recommended that exploitation on this stock not be increased (i.e. landings and discarding at sea) and that all directed catches and by-catches be recorded. These measures are vital for assessing and limiting the impact of exploitation on the stock’s reproductive potential since current fishing practices are targeting sexually immature fish.

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