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oai:figshare.com:article/34014423 2026-09-30T10:41:04Z category_30425 category_30458 category_30494 category_30500 category_30503 category_30506 category_30512 category_30530 category_30533 portal_989 item_type_18 month_year_09_2026

Joint request from the Faroe Islands, Greenland, Iceland, Norway and United Kingdom to ICES for evaluation of different rebuilding Harvest Control Rules for Atlantic mackerel ICES (11907875) Fisheries and aquaculture Arctic Ocean (ICES Ecoregion) Bay of Biscay and the Iberian Coast (ICES Ecoregion) Celtic Seas (ICES Ecoregion) Faroes (ICES Ecoregion) Greater North Sea (ICES Ecoregion) Icelandic Waters (ICES Ecoregion) Norwegian Sea (ICES Ecoregion) Oceanic Northeast Atlantic (ICES Ecoregion) mackerel Scomber scombrus mac.27.nea Technical Service sr.2026.13 harvest control rules HCR simulations rebuilding harvest control rules <p dir="ltr">A shortcut management strategy evaluation (MSE) was conducted to explore potential rebuilding harvest control rules (HCRs) for the Northeast Atlantic mackerel stock. The simulations were conducted to explore the relative short- to medium-term impacts of applying alternative HCRs to ICES Advice Rule (AR). Two sets of HCR were evaluated: HCRa (using a slope that reduces F to zero at SSB=0, with different F_min values applied for all SSBs below B_lim) and HCRb (using a slope that reduces F to zero at SSB=B_lim, with different F_min values applied). The HCRs are evaluated assuming that recruitment to the stock remains at the low levels observed for the last 10 years, and with a base case assumption that the level of advice overshoot (implementation error) would remain at the same level as observed over the last five years.</p><p dir="ltr">HCRa is identical to the ICES AR above B_lim. Below B_lim a constant low fishing mortality is used (F_min). Just below B_lim, the fishing mortality from these HCRs is lower than the F from ICES AR. Therefore, these HCRs all contain a step change in the advice at B_lim in the HCR.</p><p dir="ltr">HCRb is identical to the ICES AR when SSB is above MSY B_trigger. Below MSY B_trigger, the advised F reduces linearly and more rapidly than in ICES AR. Therefore, when the stock is below MSY B_trigger, HCRb always advises a lower F than ICES AR. When the HCR reaches F_min, advised F is kept constant and equal to F_min up to SSB = 0.</p><p dir="ltr">All tested HCRs led to spawning-stock biomass (SSB) increases in the short term (five years), but the speed and terminal level depended on the value of F_min used in the HCR. HCRs with higher F_min values resulted in less/slower rebuilding and less catch following initial big reductions in the first year. HCRb, which applies a faster reduction of F when SSB falls below MSY B_trigger, leads to slightly healthier SSB in 10 years at the cost of slightly lower catches over this period. All HCR options led to a higher probability of being above B_lim compared to the simplified ICES AR (assuming the slope of the HCR is followed) because, in the specific simulations carried out, the SSB was always in the range where the targeted F from the evaluated HCRs is either the same or lower than ICES AR.</p><p dir="ltr">In response to the three objectives specified in the request, all HCRs avoid further reductions in the stock size in the short term with a high probability. However, the ability to recover the stock above B_lim in the short to medium term with a high probability is limited, given the low recruitment level assumed in the simulations. Most HCRs get the stock above B_lim with 50% probability within two years, but none achieve this with 95% probability over the simulated period. Similarly, none achieve recovery above MSY B_trigger in 10 years.</p><p dir="ltr">Shortcut MSEs have some inherent issues due to the simplified assumptions in the observation of the population. There are also uncertainties about modelling productivity realistically for this stock, which ultimately should be explored more thoroughly through a full reference set of operating models to find an HCR that is robust to this uncertainty. The results from these evaluations should not be considered predictions for the future. Rather, it is 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> 2026-09-30T00:00:00Z Text Report 10.17895/ices.advice.34014423.v1 https://figshare.com/articles/report/Joint_request_from_the_Faroe_Islands_Greenland_Iceland_Norway_and_United_Kingdom_to_ICES_for_evaluation_of_different_rebuilding_Harvest_Control_Rules_for_Atlantic_mackerel/34014423 CC BY 4.0