Report of the Third Workshop on Redfish and Oceanographic Conditions (WKREDOCE)

The Workshop on Redfish and Oceanographic Conditions (WKREDOCE) was established as a response to a request for advice from NEAFC (Northeast Atlantic Fisheries Commission) to ICES “to analyse the distribution and abundance of pelagic redfish (Sebastes mentella) in the Irminger Sea and adjacent waters in relation to environmen-tal changes” (see Section 1.4). Prior meetings in September of 2011 and March 2012 identified possible data sources, set the objectives to address the ToR (Section 1.5) and reviewed two preliminary analyses (ICES 2011a, ICES 2012a). <br> The present meeting, WKREDOCE3, attended by ten participants (four by corre-spondence) from Canada, Germany, Iceland, Netherlands and Russia to finalize and review three analyses done intersessionally. <br> A seasonal study based on commercial data assumes that movements of the fleets reflect movement of the fish although other factors likely also affect fleet dynamics. In April-July, densest concentrations of the redfish are found primarily in the northern part of international waters of the Irminger Sea and the adjacent EEZs of Iceland and Greenland. They comprise primarily large individuals. Hydrographic conditions in the 100-800 m layer advected by the Irminger Current are: temperature, 4.3-7.7 °С; salinity, 34.9-35.2; vertical gradient of potential density under 0.44 kg/m3 km1 and 4°С isotherm depth ranging from 550 to 1350 m. The densest concentrations of the redfish in Aug.-Sept. occur in the subsurface layer of more southern areas, the Irminger Basin and the Northwest Atlantic Mid-Ocean Channel, and comprise small-er individuals. This concentration occurs in modified Atlantic waters associated with a combination of relatively reduced average temperature (3.4-6.7°С) and salinity (34.8-35.0) in 100-800 m layer, more pronounced density stratification (the potential density gradient is 0.23-0. 65 kg/m3 km1) and reduced upper layer of warm waters (4 °С isotherm &lt; 850 m). <br> Interannually, spatial distribution of S. mentella in the Irminger Sea, mainly in waters &lt; 500 m appear to be strongly influenced by Irminger Current Water (ICW) tempera-ture changes linked to the Subpolar Gyre (SPG) and the North Atlantic Oscillation (NAO). The fish avoid increasing volumes of ICW (&gt;4.5ºC and &gt;34.94) in the north-eastern Irminger Sea due to an intensification of the SPG by displacing towards the southwest, to more fresher, colder waters. A weakening of the SPG has the opposite effect. The time-lag between SPG intensification and ICW temperature change is around 2 years, while the time-lag between the latter and the fish displacements is around 1 year. ICW temperature increase from April to September parallels the sea-sonal fish displacements southwestward at the end of the fishing season as observed with the positions of the commercial fishing fleets. The influence of LSW on fish dis-placement has also been considered. While LSW volume changes are strong at the interannual time-scale and roughly simultaneous with fish stock displacements, the influence of LSW seems weak in comparison to ICW. <br> A Habitat Suitability Index (HSI) model was used to assess the capacity of the Irminger Sea habitat to support adult S. mentella. It was found that temperature and salinity are sufficient to describe the distribution down to depths of 500 m. However, additional variables are expected to have an influence on the distribution of this species. The results at the seasonal and interannual time-scale are concordant, such that the SPG increases intensity towards autumn and winter, concentrations of fish to displacing southwestward in certain (warmer) years and at the end of the fishing season. <br> These analyses are used as the basis of the advice to NEAFC. Analyses on effect of changes in oceanographic conditions on abundance of S. mentella were not possible at this time. <br> The originally arranged log Gaussian Cox model of with spatial correlation and hydrographic effects analysis was not completed.

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