Research Document - 2011/057
Production model fitting and projection for Atlantic redfish (Sebastes fasciatus and Sebastes mentella) to assess recovery potential and allowable harm
By M. McAllister and D.E. Duplisea
A recovery potential analysis was carried out for stocks of Atlantic redfish falling within three designatable units recently assessed by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) as either threatened or endangered. A state-space Schaefer surplus production model was fitted to trawl survey biomass estimates considered as relative indices of abundance for these different stocks. Bayesian methods were applied for parameter estimation, evaluation of stock status and stock projections for three populations of Acadian redfish, Sebastes fasciatus, and two populations of deepwater redfish, Sebastes mentella, on the Atlantic coast of Canada for the purpose of assessing recovery potential. This stock assessment methodology has been previously applied to 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. Though apparently an esoteric methodological detail, allowing a process error estimate for each year means that the model can incorporate irregular population processes such as spasmodic recruitment events which seem to characterise Atlantic redfish populations and which can invalidate non-state-space implementations of production models.
Results suggest that the Laurentian Channel population of S. mentella is presently in a very low biomass state with a 0% chance of being above 40% of the most productive stock biomass level (0.4 Bmsy) while the northern population is doing only slightly better with 1% chance of being above this level. There would appear to be little prospect for any allowable harm on the Laurentian channel population if the goal is to increase the biomass of the stock even to only 40% of Bmsy. The situation is only slightly better for the northern population.
Results suggest that populations of S. fasciatus, are not nearly in such a poor state as S. mentella and the southern population in Unit 3 would appear to be healthy. The Laurentian Channel-Grand bank population of S. fasciatus would appear to be able to support a directed fishery when considered as a unit stock. The 2J3K population of S. fasciatus is not very abundant and even small fisheries on this stock would slow down its recovery to 40% Bmsy. S. fasciatus, taken as a whole as the Atlantic designatable unit, would appear to have a very low risk of extinction and in most places could support directed fishing.
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