Research Document - 2007/085

Review of the structure, the abundance and distribution of Sebastes mentella and S. fasciatus in Atlantic Canada in a species-at-risk context: an update

By J.-M. Sévigny, R. Méthot, H. Bourdages, D. Power, and P. Comeau

Abstract

This document presents the information reviewed and analyzed by Fisheries and Oceans (DFO) that can be used by the Committee on Status of Endangered Wildlife in Canada (COSEWIC) in assessing status and extinction risk of the two main redfish species (Sebastes fasciatus and S. mentella) in the Northwest Atlantic. Redfish population structure was evaluated in the context of Evolutionarily Significant Units (ESU). The review did not provide evidence of the existence of ESUs within current management units. Therefore, all the analyses were carried out on the actual unit stocks. Methods developed to separate redfish by genotype (for Unit 1-3) or meristics (for NAFO Divisions 2GHJ3KLMNO) were applied to the research vessel survey data to obtain abundance indices. Three distribution indices were calculated: the area of occupancy, the minimum area occupied by 95% of the stock, and the Gini index of aggregation. No general pattern or trend in geographic distribution was evident. The Unit 1 stock experienced a substantial decline at the beginning of the 1990 and has not recovered yet. However, a new year-class (2003), which seems to be quite important, was observed since the 2005 survey. The stock in NAFO Divisions 2GHJ 3K experienced declines but has shown some signs of recovery. The redfish stocks in remaining management units have not shown signs of decline or the information available for these stocks may not reflect the abundance. Fishery and/or the lack of recruitment were considered the main causes of abundance decline for the stocks in Unit 1 and in NAFO Div. 2GHJ 3K. However, environmental changes and elevated natural mortality were also identified as possible causes of decline. Mature population abundance indices of all redfish stocks in Atlantic Canada are at from one to three orders of magnitude greater than the COSEWIC threshold of 10 000 mature individuals.

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