NEAFC request to provide information on the stock structure of Sebastes mentella fished in pelagic and demersal fisheries, i.e. relationship between the redfish in ICES Areas I, II, V, VI, X, XII, and XIV and the NAFO regulatory area

ICES has reviewed the stock structure of Sebastes mentella in the Irminger Sea and adjacent areas. As noted by NEAFC, a Workshop on Redfish Stock Structure, WKREDS (ICES, 2009), was formed to review all available material on the stock identity of the various redfish units (Sebastes mentella) in the Irminger Sea and adjacent waters, to identify the most likely definition of biological stocks of S. mentella, and to suggest practical management units. One of the primary reasons for the formation of such an expert group was to reconcile recent information on genetic differences within S. mentella with all other information on stock structure, including previous genetic research, life-history patterns, phenotypic variation, and connectivity. In undertaking this review, ICES acknowledges the substantial scientific progress made by previous international and national initiatives to address the issue of stock structure of redfish in the Irminger Sea and adjacent areas. The chronological advancement of research on S. mentella is parallel with fishery development. The approach now used by ICES is to define all a priori hypotheses on redfish stock structure in the Irminger Sea informed by previous reviews, science and advisory decisions. Hypotheses were posed as one-, two-, and three-stock scenarios, with variations in some scenarios; followed by a review of the science related to population structure. The science information examined included aspects of geographic distribution (e.g. fishing grounds, survey data of early life-stages, juveniles and adults), genetic variation (e.g. allozymes, mitochondrial DNA, and nuclear DNA), phenotypic variation (e.g. life-history traits, morphology, and fatty acid composition), and connectivity (e.g. larval dispersal, natural tags (parasites, and otolith structure and chemistry) and artificial tags) and was used to develop a general conclusion about stock structure. Each of the a priori hypotheses was considered with respect to these various aspects and the conclusion about stock structure was based on the weight of the evidence provided by the body of information. Based primarily on genetic information; i.e. microsatellite information, and supported by analyses of allozymes, fatty acids, as well as some parasite patterns; ICES concludes that there are three biological stocks of S. mentella in the Irminger Sea and adjacent waters:

2) a ‘Shallow Pelagic’ stock (NAFO 1–2, ICES V, XII, XIV <500 m) – extends to ICES I and II, but primarily pelagic habitats, and includes demersal habitats east of the Faroe Islands;

3) an ‘Icelandic Slope’ stock (ICES Va, XIV) – primarily demersal habitats.

Adult redfish on the Greenland Shelf have been attributed to several stocks and there remains a need to investigate the affinity of the adult S. mentella in this region. The east Greenland Shelf is most likely a common nursery area for the three biological stocks.