Research Document - 2004/058

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

By Morin, B., Methot, R., Sevigny, J.-M., Power, D., Branton, B., McIntyre, T.

Abstract

This document presents the information reviewed and analyzed by Fisheries and Oceans (DFO) that could be used by the Committee on Status of Endangered Wildlife in Canada (COSEWIC) in assessing status and extinction risk of the two main species of redfish (Sebastes fasciatus and S. mentella) in the Northwest Atlantic. Redfish population structure was evaluated in the context of "evolutionarily significant units". The review did not provide evidence to indicate the existence of ESUs within current management units, therefore all the analyses were realized on the current unit stocks. Methods have been developed to separate redfish by genotype and applied to the research vessel (RV) 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. One stock experienced a substantial decline and had not recovered (Unit 1). One stock experienced declines but has shown some recovery (NAFO divisions 2GHJ 3K). The remaining management units have not shown a decline or the information available may not reflect the abundance. Fishery exploitation and the lack of recruitment were considered the main causes of abundance decline for two stocks (Unit 1 and 2GHJ 3K), although environmental changes and elevated natural mortality were identified as possible factors. Mature population abundance indices of all redfish stocks in Atlantic Canada are at least two orders of magnitude greater than the COSEWIC threshold of 10 000 mature individuals.

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