Joint request from EU and UK on the impacts of different rebuilding harvest control rules (HCRs) for selected depleted stocks caught in mixed fisheries in the Celtic Sea and Eastern Channel

Biomass increases under all HCRs after an initial decline, while catches are expected to decrease in 2027–2028 before recovering.</p><p dir="ltr"><b>Haddock in divisions 7.b–k (southern Celtic Seas and English Channel)</b>: Continued low recruitment is projected to prevent stock rebuilding, with median SSB remaining below B_lim under all HCRs throughout the simulation period. Catches are expected to decline to very low levels, and even the most precautionary HCRs only produce modest biomass increases.</p><p dir="ltr"><b>Whiting in divisions 7.b–c and 7.e–k (southern Celtic Seas and western English Channel)</b>: All HCRs result in moderate increases in SSB during the first decade, but none rebuild the stock above B_lim.

More precautionary HCRs provide the highest probability of stock improvement, while catches are projected to decrease initially and recover only moderately thereafter.</p><p dir="ltr"><b>Plaice in Division 7.d (eastern English Channel)</b>: SSB is projected to increase above B_lim within 2–3 years under all HCRs, although higher F_minvalues slow this increase. However, none of the HCRs are expected to rebuild the stock to MSY B_trigger.</p><p dir="ltr"><b>Sole in Division 7.d (eastern English Channel)</b>: All HCRs are projected to increase SSB above B_lim in the medium term, with faster increases occurring under lower F_min values.</p><p dir="ltr">None of the HCRs rebuild the stock to MSY B_trigger, and the results reveal a trade-off between larger short-term catch reductions and improved long-term stock status and catches.

Compared to a full MSE, shortcut MSEs have inherent limitations because of simplified assumptions regarding assessment model error as well as observation error. Uncertainty about these errors may have a substantial effect on the estimated probabilities, including the probability of SSB falling below B_lim, but will generally have less effect on trends and median values. There are also uncertainties about modelling productivity realistically for these stocks, and this should ultimately be explored more thoroughly through a full reference set of operating models to find HCRs that are robust to these uncertainties.

The results from these evaluations should not be considered predictions for the future. Rather, these analyses are an intermediate step between a short-term forecast (as done by ICES to provide annual catch advice) and full MSE. Results are sufficient to draw comparisons between alternative HCRs and can be used to guide decisions on interim measures until a full MSE can be conducted.</p><p><br></p>