Benchmark Workshop on selected stocks in the Western Waters in 2021 (WKWEST)
reportposted on 2021-06-03, 00:00 authored by ICESICES
The Benchmark Workshop for selected Western Stocks (WKWEST), met to progress towardachieving updated assessment methods. Five stocks were proposed for benchmark throughWKWEST, plaice (Pleuronectes platessa) in in ICES divisions 7 h–k (ple.27.7h–k), sole (Solea solea)in divisions 8.c and 9.a (sol.27.8c9a), sardine (Sardina pilchardus) in Subarea 7 (pil.27.7), red gurnard(Chelidonichthys cucculus) in subareas 3 to 8 (gur.27.3–8) and Pollack (Pollachius pollachius)in subareas 6–7 (pol.27.67). Following the data evaluation and progress meeting, it was consideredthat the issues identified that changes and improvement for the assessment methods of pollackwould not be possible. In response to this, the issue list for the stock was updated. It wasproposed that this stock would not be taken to the benchmark meeting and that more work wasneeded. Prior to the benchmark, plaice was considered a data poor, assessed as a category 3stock. The issues identified prior to the benchmark were focused achieving adoption of a moreappropriate assessment model with better data coverage of the assessment area, including discardestimates and to explore development of tuning series. The outcome of the benchmark improvedthe ability to effectivity assess the status of plaice in 27.7h–k. Although the stock is proposedto remain as category 3, the improvements to the quality of data and assessment methodmean that the complete stock area (27.7.h–k) can be assessed. A newly developed survey indexfor this stock provided some important stability to our perception of this stock. The collatedcommercial and survey data enabled estimation a number of important life history parametersfor this stock. The final assessment method selected for this stock was stochastic surplus productionmodel in continuous time (SPiCT). This method provided stock trends and biological referencespoints, which were then used to provide category 3 advice for this stock. Red gurnard hasbeen considered a Category 6 stock. During WKWEST a newly developed index of abundancemade it possible to assess the stock as an ICES category 3 stock. Issue persist with regard toconfidence of the landing series due to ‘mixed’ species reported landings, although it was consideredthat these data could be used to provide a precautionary understanding of harvest level.WKWEST concluded and agreed way of assessing the stock: Trend-based assessment using thecombined biomass index of the delta lognormal GLM model. Fproxy (ratio of landings / biomassestimate) as an indicator of harvest level. Prior to the benchmark, the sardine assessment wasclassified as category 5. The aim of benchmark was to improve and assure the data quality andexplore potential tuning series. WKWEST concluded that the landings and the biomass data providedby the PELTIC survey were appropriate to assess the stock and provide advice. The availabilityof the biomass data to assess the stock implies an upgrade of stock category, being nowclassified as category 3. Consequently, the ICES guidance on advice rules for stocks of shortlivedspecies in category 3 were explored. The benchmark agreed that a SPiCT model can be usedto assess the status of the stock based on the relative biomass and fishing mortality to the referencepoints (BMSY, FMSY). However, given the high uncertainty associated with absolute values ofbiomass, fishing mortality and reference points, the model is not appropriate to provide advice.Prior to the benchmark sole was considered a data-limited stock, and it was classified as category5 stock, as only catch data were available. There was no analytical assessment for sole in this areaprior to WKWEST. At WKWEST among all the data-poor methods implemented (i.e., LBI,LBPSR, MLZ and SPiCT) it was agreed that the LBI approach was currently the most adequatefor this stock. An index of biomass is was developed agreed as the weighted sum of the PortugueseLPUE and the Spanish Bayesian survey index.
Published under the auspices of the following ICES Steering Group or Committee