Benchmark workshop on selected megrim stocks (WKMEGRIM; outputs from 2022 meeting)
The main aim of the ICES WKMEGRIM benchmark was to standardize, increase transparency, and review the input data of the assessment for three megrim stocks; namely two Lepidorhombus whiffiagonis stocks in divisions 7.b-k, 8.a-b, and 8.d (meg.27.7b-k8abd) and divisions 8.c and 9.a (meg.27.8c9a), as well as L. boscii in divisions 8.c and 9.a (ldb.27.8c9a).
For all three stocks, the data collection methods were reviewed, the biological data (maturity and length-weight relationships) were updated based on newly available data, a variety of tuning indices were considered, and new assessment frameworks were employed and configured.
Scrutiny applied to historic data lead to re-assessing how discard data and catches of recruits were treated in the assessment, where catches of recruits reported from old monitoring programmes were removed and set to be estimated in the assessment model. New maturity ogives based on best-practice histological methods were adopted and the use of female-only ogives were selected. Fisheries independent surveys were available, sufficient, and often better (without inexplicable deviations) for all stocks. Therefore, only fisheries independent surveys were utilized as tuning fleets in all assessments. Recent improvements to standardizing the commercial tuning fleets for the southern stocks means these may remain valuable as an independent data source for consideration during assessment working groups. Bespoke and out-dated mechanistic assessment model frameworks were abandoned and statistical catch-at-age models were adopted, using the A4A framework, for all stocks. This results in more reproducible, transparent and easier to run assessments.
Future research should focus on differentiating between the sexes in both megrim and four-spot megrim stocks (e.g. growth, maturity, fishery selectivity, habitat and spatial distribution). Preliminary evidence from a new Irish anglerfish and megrim survey points towards substantial differences between the sexes that may warrant sex-specific assessments.
Published under the auspices of the following ICES Steering Group or Committee