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Report2025

Benchmark Workshop on Selected North Sea and Celtic Sea Stocks (WKBNSCS)

ICES; et al.

Abstract

The objective of this benchmark process was to evaluate the assessment methods and data for three stocks: Plaice in Division 7.d (eastern English Channel), turbot in Subarea 4 (North Sea), and whiting in Division 7.a (Irish Sea).

Input data were extensively reviewed during the data workshop. Revisions were made to landings and discard data as well as the methodology behind the derivation of the stock biomass indices, stock and catch weights, maturity estimates and natural mortality for all three stocks. All the terms of reference were covered and an agreement was reached on the data to use for assessments, projections and reference points of each stock reviewed.

Whiting 7.a and plaice 7.d were previously assessed using an Age-Structured Assessment Programme (ASAP) and a statistical catch at age model (AAP) respectively. At the end of the workshop, all three stocks opted for an age-based analytical Stock Assessment Model (SAM). For plaice 7.d, this addressed the strong patterns in residuals of the survey indices and catch. Turbot 4 was already using a SAM model, but changes to the survey indices (including the addition of an industry-science collaborative index, combining several scientific surveys into one index and removing the Dutch commercial LPUE index), and internally modelled weights-at-age resulted in a better fit and resolved the issue of accumulating biomass in the plus group. For whiting 7.a, SAM better accommodated the gradual changes in selectivity that occurred in the fishery over the time series. Recreational catch estimates were included in the assessment for the first time.

For all stocks, model fit, and retrospective model runs revealed no substantial patterns. Sensitivity runs were conducted to investigate to key model assumptions and the workshop agreed on the final model configuration. The workshop further agreed on the methods used to calculate reference points and forecasts. For whiting 7.a, it was deemed necessary to re-evaluate the reference points regularly due to the uncertainty regarding the effect of a regime shift that happened in the Irish Sea. An MSE evaluation to test robustness of these estimates was recommended.

Published in

ICES scientific reports
2025, number: 7:42
Publisher: International Council for the Exploration of the Sea

SLU Authors

UKÄ Subject classification

Fish and Wildlife Management

Publication identifier

  • DOI: https://doi.org/10.17895/ices.pub.28715180

Permanent link to this page (URI)

https://res.slu.se/id/publ/141406