Inter-Benchmark Workshop on NEW species (IBPNEW) met in Copenhagen (Den-mark) from 1–5 October 2012 to perform a benchmark assessment on the stocks of turbot and sea bass. All the terms of reference were addressed. In hindsight, the five days that were available for this workshop were too short. Although most work re-garding the ToRs was finished before the end of the workshop, large parts of the report still needed to be finished at the end of the meeting, and this caused consider-able delay in the delivery of the final report. For turbot in the North Sea ecoregion, the group recommends that turbot from the Skagerrak/Kattegat is not included in the Greater North Sea stock, but treated sepa-rately or combined with the Baltic stock. This recommendation is based on considera-tions of the life-history characteristics of turbot (low larval dispersal, strong spawning site fidelity, limited migrations of the species) and the observed genetic patterns. The western limit of the North Sea stock would remain between IVc and VIId. Further progress on the assessment of turbot in IIIa could be made in WGNEW or WGBFAS. Landings, effort and survey index data for Turbot in Area IV were collated. These data were made available by earlier working groups and projects, such as ICES WGNEW and the NESPMAN project. Two different stock assessments were per-formed on the data: ASAP (NOAA toolbox) and a spline-based statistical catch-at age model. The spline-based statistical catch-at-age model was proposed as a model to be used in future WGNSSK groups. The model is run on the landings-at-age data avail-able since 1975 combined with the BTS-ISIS and SNS survey indices and the Dutch beam trawl fleet cpue as tuning indices. Given the assessment model results, the FMAX reference point on the yield-per-recruit curve was estimated and was well-defined. The assessment results indicate that the fishing mortality in the most recent years has been higher than FMAX. No short-term forecast methodology was proposed, and when used for management advice, WGNSSK should decide on a short-term forecast methodology. For sea bass in the Northeast Atlantic, the group only had sufficient data to carry out an analytical assessment for populations in the North Sea (IVb&c) and in the Irish Sea, Channel and Celtic Sea (VIIa,d,e,f,g&h). The group concludes that sea bass in the Irish coastal waters of ICES Divisions VIIb,g&j and in VIa, and in the Bay of Biscay (VIIIa&b) and farther south (VIIIc & IXa), should be treated as functionally separate populations, but has insufficient data to develop analytical assessments for these areas. There is no clear basis from fishery data, tagging and genetics studies to subdi-vide the populations in the Irish Sea, Celtic Sea, Channel and North Sea, although the group acknowledges the existence of fine-scale spatial structuring of immature sea bass, and of adults during the non-spawning period, due to strong site fidelity. The statistical assessment model Stock Synthesis 3 was used to estimate trends in abun-dance and fishing mortality for sea bass in the combined area using trawl survey indices of abundance-at-age for young bass, fleet-disaggregated length and age com-positions for the UK fisheries from 1985 onwards, and length compositions for French fleets. Limited data on UK and French discards were also available for recent years. Insufficient data were available on recreational catches for inclusion in the assess-ment, although estimates for France and the Netherlands in 2010 indicate that recrea-tional fisheries could account for as much as 20% of the fishing mortality. A wide range of sensitivity runs of the Stock Synthesis model using different combinations of Inter-Benchmark Workshop on NEW species (IBPNEW) met in Copenhagen (Den-mark) from 1–5 October 2012 to perform a benchmark assessment on the stocks of turbot and sea bass. All the terms of reference were addressed. In hindsight, the five days that were available for this workshop were too short. Although most work re-garding the ToRs was finished before the end of the workshop, large parts of the report still needed to be finished at the end of the meeting, and this caused consider-able delay in the delivery of the final report. For turbot in the North Sea ecoregion, the group recommends that turbot from the Skagerrak/Kattegat is not included in the Greater North Sea stock, but treated sepa-rately or combined with the Baltic stock. This recommendation is based on considera-tions of the life-history characteristics of turbot (low larval dispersal, strong spawning site fidelity, limited migrations of the species) and the observed genetic patterns. The western limit of the North Sea stock would remain between IVc and VIId. Further progress on the assessment of turbot in IIIa could be made in WGNEW or WGBFAS. Landings, effort and survey index data for Turbot in Area IV were collated. These data were made available by earlier working groups and projects, such as ICES WGNEW and the NESPMAN project. Two different stock assessments were per-formed on the data: ASAP (NOAA toolbox) and a spline-based statistical catch-at age model. The spline-based statistical catch-at-age model was proposed as a model to be used in future WGNSSK groups. The model is run on the landings-at-age data avail-able since 1975 combined with the BTS-ISIS and SNS survey indices and the Dutch beam trawl fleet cpue as tuning indices. Given the assessment model results, the FMAX reference point on the yield-per-recruit curve was estimated and was well-defined. The assessment results indicate that the fishing mortality in the most recent years has been higher than FMAX. No short-term forecast methodology was proposed, and when used for management advice, WGNSSK should decide on a short-term forecast methodology. For sea bass in the Northeast Atlantic, the group only had sufficient data to carry out an analytical assessment for populations in the North Sea (IVb&c) and in the Irish Sea, Channel and Celtic Sea (VIIa,d,e,f,g&h). The group concludes that sea bass in the Irish coastal waters of ICES Divisions VIIb,g&j and in VIa, and in the Bay of Biscay (VIIIa&b) and farther south (VIIIc & IXa), should be treated as functionally separate populations, but has insufficient data to develop analytical assessments for these areas. There is no clear basis from fishery data, tagging and genetics studies to subdi-vide the populations in the Irish Sea, Celtic Sea, Channel and North Sea, although the group acknowledges the existence of fine-scale spatial structuring of immature sea bass, and of adults during the non-spawning period, due to strong site fidelity. The statistical assessment model Stock Synthesis 3 was used to estimate trends in abun-dance and fishing mortality for sea bass in the combined area using trawl survey indices of abundance-at-age for young bass, fleet-disaggregated length and age com-positions for the UK fisheries from 1985 onwards, and length compositions for French fleets. Limited data on UK and French discards were also available for recent years. Insufficient data were available on recreational catches for inclusion in the assess-ment, although estimates for France and the Netherlands in 2010 indicate that recrea-tional fisheries could account for as much as 20% of the fishing mortality. A wide range of sensitivity runs of the Stock Synthesis model using different combinations of datasets and model settings indicate a recruitment-driven increase in spawning–stock biomass from the early 1990s up to the mid-2000s, followed by a decline in SSB coin-cident with increasing fishing mortality during the 2000s. Recent year classes since 2008 appear very weak. A comparative ASAP run (NOAA toolbox) using UK age composition data applied to all other international landings showed similar stock trends to the Stock Synthesis model. Short-term projections were not carried out, although the scenario of increasing F, declining SSB and very poor recruitment since 2008 would lead to an expectation of further SSB decline. The group recommends continued use of Stock Synthesis for provision of trends-based advice by WGNEW and that procedures for carrying out trends-only projections should be developed at WGNEW 2013. Finally, the group discussed whether trying to control fishing mortality for species such as sea bass and turbot through TACs is an effective strategy: if fishing continues while quota are exhausted, large incentives for overquota discarding are created. Fishing effort reductions on those fleets taking these species as bycatch are probably a more effective measure for reducing fishing mortality. For turbot in the North Sea, such fishing effort reductions are foreseen in the management plans for some of the target species, such as the long-term management plan for sole and plaice in the North Sea, and the management plan for cod. Meanwhile, the assessment results indicate that higher yields for turbot are possible if the gear and fishing patterns of the important fishing fleets taking this species are altered to selectively reduce the catches of small turbot.