Research Document - 2012/103
Production model fitting and projection for Acadian redfish (Sebastes fasciatus) in Units 1 and 2
By M. McAllister and D.E. Duplisea
A state-space Schaefer surplus production model was fitted to trawl survey biomass estimates considered as relative indices of abundance for the Laurentian Channel (Unit 1+2) Sebastes fasciatus. Bayesian methods were applied for parameter estimation, evaluation of stock status and stock projections for the purpose of assessing recovery potential. This methodology has been previously applied to Atlantic Acadian and deepwater (S. mentella) redfish in an RPA of stocks in five Atlantic east areas and other Sebastes species on the Pacific coast of Canada. The state-space version of this model allowed for the inclusion of process error which can account for deviations in dynamics from surplus production assumptions.
Results suggest that the Laurentian Channel population of S. fasciatus is presently in a low biomass state with a 7% chance of being above 40% of the most productive stock biomass level (0.4 Bmsy) in 2011. There appears to have been an increasing trend in stock size in recent years and the 2011 catch of 1,250 tons is well below the posterior median estimate of replacement yield of about 6,500 tons.
Results suggest the Laurentian Channel population of S. fasciatus is well into the critical zone (assuming a lower reference point (LRP) of 0.4 Bmsy) though it is able to support the current fishery and see continued increases in abundance when considered as a unit stock. Other work indicates that the Unit 1 and Unit 2 area may have important substock structure and some components of the stock (Unit 1) appear to be more depleted than others. Fishing or allowable by-catch on this stock should account for its overall status as well as that of sub-components.
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