WKBASS is a three-part benchmark workshop aimed at improving the scientific advice on sea bass (Dicentrarchus labrax) stocks in the Bay of Biscay (BSS-8.ab: ICES areas 8.a,b) and in the North Sea, Channel, Celtic Sea and Irish Sea (BSS-47: ICES areas 4.b,c and 7.a, d–h). This report is of the first workshop which focused on the compilation and evaluation of data available for use by the assessment workshop. The workshop, at ICES HQ, was attended physically and remotely by six scientists from France and the UK, and by the ICES secretariat. The data compilation and evaluation was done in Jan-uary 2017, followed by assessment workshops in February 2017 and February 2018. There were concerns following the first assessment workshop in February 2017, so the methodology was finalised at the second assessment workshop in February 2018. As a result, additional data and analyses were available at the second assessment workshop, but this report reflects the evaluation of data in January 2017. Any additional data or changes to the way that the data were compiled and used for the second assessment workshop in February 2018, are captured in the WKBASS assessment report.
The Biscay stock has not previously been benchmarked. WKBASS compiled and re-viewed all available information and data relevant to the assessment, including: the history of fishery management measures; biological parameters (growth, maturity, natural mortality); commercial and recreational fisheries catch and length/age compo-sitions; survival of released fish; fishery selectivity patterns; relative abundance indi-ces; and environmental drivers. Data quality indicators such as coefficients of variation or numbers of primary sampling units, where available, were tabulated.
WKBASS identified the most appropriate data and compiled these in a form suitable for use in assessment models, with particular focus on use of the Stock Synthesis inte-grated modelling framework. Candidate values for age-dependent natural mortality (M) were reviewed using published life-history based methods, using the Lorenzen (1996) method to infer age-dependence in younger fish and maximum observed age to scale the M vector to appropriate values for older sea bass. A fishery-dependent land-ings-per-unit-of-effort (lpue) series of relative abundance indices was derived starting in 2000, using generalized linear modelling (GLM) of trip-based data for over 1000 French vessels within selected ICES rectangles and gear types covering the sea bass fishery. This provided lpue series for French vessels fishing on the BSS-47 stock in the Celtic Sea, Channel, and southern North Sea as well.
For the BSS-47 stock, the main focus of WKBASS is the evaluation of biological refer-ence points such as FMSY and MSY-Btrigger, as this was not completed in the most recent inter-benchmark (IBPBASS in 2016). Many of the datasets and parameters for this stock have been thoroughly reviewed in the previous inter-benchmarks, and WKBASS did not revisit these unless it was relevant to biological reference points (e.g. natural mor-tality values) or for addressing issues that may arise with the current assessment for-mulation such as impacts of new management measures in 2015 and 2016 which will impact the formulation of the model and forecasts.
Recreational fishery survey data were reviewed and updated with new data from the Netherlands, and the French survey data collected in 2011/2012 were disaggregated to give separate estimates for areas 7 and 8. WKBASS considered ways in which the changes in management measures for the BSS-47 stock in 2015 and 2016 (increased minimum conservation reference size from 36–42 cm and imposition of recreational fishery bag limits) could be dealt with in the update assessment for this stock in 2017. Information on post-release mortality of recreational-caught sea bass was compiled from the limited studies available. WKBASS reviewed progress on compilation of evi-dence on stock structure in Areas 4, 7 and 8 from ongoing tagging and genetics studies, to be submitted in a working document to the second (assessment) workshop.