Science Advisory Report 2011/001
Assessment of Atlantic Halibut on the Scotian Shelf and Southern Grand Banks (NAFO Divisions 3NOPs4VWX5Zc)
Summary
- A new framework was used to asses the stock status of Atlantic halibut and the impact of the fishery. A length-based, age-structured catch-at-length (CAL) model was fitted to the total catch, length compositions in the catch and to the catch rate and length composition of halibut caught in the Scotia-Fundy Groundfish Research Vessel (RV) survey (1970-2009) and halibut survey (1998-2009).
- Catch rates in the groundfish RV survey have increased since 2002, with the 2010 catch rate being the highest recorded in the 40 year time series. Most of these fish are expected to enter the fishery in two years and recruit to the spawning stock biomass within approximately five years.
- Based on the catch rate analyses of the halibut survey, the population of 3NOPs4VWX5Zc Atlantic halibut has been steadily increasing over the past 5 years, with a slight decrease in 2010.
- Model estimates indicate high population biomass and recruitment in the 1970s, increased biomass, but poor recruitment in the 1980s, low biomass and recruitment in the 1990s, and increasing biomass and recruitment in the 2000s. The spawning stock biomass (SSB) in 2009 was estimated at 6527t (2592t for females).
- Fully-recruited fishing mortality was about 0.2 for the longline and otter trawl fisheries in 1970, but rapidly increased to 0.4 or greater in the late 1980s and early 90s as the population decreased. Fully-recruited fishing mortality was 0.2 in 2009.
- Tagging data was used to estimate natural and fishing mortality making different assumptions and using different subsets of the data. Fully-recruited fishing mortality estimates from the assessment model were comparable to estimates from tagging (F = 0.20, 0.29, 0.21 for 2007, 2008 and 2009). Natural mortality was estimated to be 0.26, which is thought to be high given longevity of 40 years or more.
- Reference points (BMSY, FMSY) were estimated from the virtual population analyses (VPA) and CAL models. Both models gave similar results (BMSY=4900t, FMSY=0.36).
- Based on the assessment model results, the 3NOPs4VWX5Zc Atlantic halibut population is in a productive period due to high recruitment. The SSB is estimated to be in the healthy zone; above the BMSY. Current fishing mortality (0.2) is well below FMSY (0.36). Although catch projections were not made, recent high recruitment would be expected to result in higher SSB at the current fishing mortality rate in the near term.
This Science Advisory Report is from the Fisheries and Oceans Canada, Canadian Science Advisory Secretariat, regional advisory meeting of November 16-17, 2010 on the Assessment of Atlantic Halibut on the Scotian Shelf and Southern Grand Banks (Div. 3NOPs4VWX+5Zc). Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule.
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