WKNSROP met to reconsider the autumn reopening protocol for North Sea stocks. The workshop evaluated the historical performance in relation to delivering improved recruitment estimates for short-term forecasts, and found it acceptable for cod, haddock, plaice and sole, but less so for whiting and saithe (although there were some mitigating factors for these). Increasing the D threshold used to trigger reopening above its current value of 1 did not lead to an increase in overall performance, and therefore it is recommended to stay at 1, unless there was a desire to lower the frequency of reopening, in which case it could be set at 2. The consistency of application, method used, and justification for ages used in the reopening protocol check were also evaluated. The continued use of RCT3 under default settings for the reopening check (apart from taper weighting that may be required for saithe), using an R package (rct3) maintained on the ICES GitHub repository, was recommended, along with using only a single age (usually the
youngest age in the assessment, except for saithe) in the reopening check, and using the entire time series of corresponding assessment estimate in the RCT3 regression, apart from where the most recent estimate is considered too uncertain to be used (e.g. for cod, plaice and sole). One of the primary objectives of the workshop was to consider whether any information available during the intermediate year (the year WGNSSK meets and formulates advice for the following year) could be used to improve short-term forecast assumptions about fishing mortality. The most useful, and potentially readily available, source of information was reported landings up to the third quarter of the intermediate year, which were found historically to correlate strongly with landings for the full year (with r2 values exceeding 0.9 in most cases). If such information were available to be used, then an additional reopening check for the intermediate year fishing mortality assumption would be needed, and several thresholds were tested (comparing the spring landings assumptions with the predicted annual landings based on the quarter 1-2 or 1-3 landings); the choice of threshold (e.g. 10, 15 or 20% difference for triggering reopening) would depend on the desired trade-off between frequency of reopening and accuracy of forecast assumptions. The workshop also discussed the need for reopening in the first place, given that it would be better, from the point of view of using the most up-to-date data and information, and saving workload, to only run the assessments and forecast, and provide advice once in the autumn. This was particularly the case for Nephrops, for which the spring advice only differs slightly from the preceding autumn advice, because the summer surveys have the biggest impact on the assessments, and data for these are only available for the autumn. It was therefore recommended that
ICES once again discusses with clients the need for spring advice. The final result of the workshop was a revised reopening protocol, which includes the use of landings data for the intermediate year, if available.
Abstract Brown crab (Cancer pagurus) is a widely distributed crustacean that occurs around the British coastline supporting important commercial fisheries. The habitat preferences of brown crab around Scotland are poorly documented and for the purposes of stock assessment, the species is considered data-poor. Based on an analysis of dredge and trawl surveys taking place in the North Sea (2008–2018), we describe the spatial distribution of brown crab and for the first time, develop abundance and recruitment indices for the species. We make use of geostatistical methods and apply generalized additive models to model catch rates in relation to a number of explanatory variables (depth, distance to the coast, sediment type and year). The dredge and trawl abundance indices were correlated showing a similar trend of increasing catch rates in the early years of the time series up to 2016 and a subsequent reduction. The recruitment index showed a gradual increase in captured juvenile crabs up to 2014 followed by a steep decrease with 2018 being the lowest value estimated. The derivation of robust indicators of stock abundance will contribute to the stock assessment of this species and enable the provision of improved fisheries management advice for brown crab around Scotland.
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