Benchmark Workshop for anchovy stocks (WKBANSP)

The Benchmark Workshop on anchovy stocks (WKBANSP) evaluated the assessment (input data and methodology), short–term forecast procedures and reference points for two anchovy stocks, Anchovy (Engraulis encrasicolus) in Subarea 8 (Bay of Biscay) and Anchovy (Engraulis encrasicolus) in Division 9.a (Atlantic Iberian waters). The key focus has been on evaluating stock structure and applying new modelling approaches for the assessments of the stocks. The assessment of anchovy in Subarea 8 was a category 1 assessment using the CBBM model. The assessment for anchovy in 9.a applied two category 3, constant harvest rate rules for short lived stocks, for the western and southern components.

Anchovy in Subarea 8

The previous stock assessment for anchovy in Subarea 8 was carried out using a Bayesian two-stage biomass-based model (CBBM) and used biomass estimates. The new assessment is carried out in the integrated statistical catch at age model Stock Synthesis (SS3) and uses numbers instead of biomass as input data. This model is faster to run and offers more flexibility for modelling the stock and the fishery, and can deal with a wider range of ages, from age 0 to 3+. This shift in the modelling approach required changes in parametrization and in the data inputs. Comparisons were made between SS3 and CBBM outputs using the same input data and showed similar stock trajectories. This assessment uses data by semester and inputs include, commercial fishery data (modelled as independent fleets by semester), two acoustic surveys (PELGAS on adults and JUVENA on recruits) and one daily egg production method spring survey (BIOMAN). Extensive model investigations were conducted and looked at catchability, selectivity, natural mortality, effective sample size and stock recruit modelling. A final model formulation with good diagnostics and acceptable retrospective patterns was discussed and agreed by the group. Further work was carried out on reference points and several options were presented and discussed in detail with the group reaching agreement on the final proposal. Due to time constraints the short term forecast discussions were deferred to WGHANSA. Recommendations for further investigations are outlined in the reviewers’ report.

Anchovy in Division 9a

The stock structure of anchovy in division 9a was extensively reviewed. WKBANSP made the decision to split anchovy in 9a into two stocks with separate assessments and advice.

· Anchovy (Engraulis encrasicolus) in subdivision 9.a South (Gulf of Cadiz) with advice provided in November.

· Anchovy (Engraulis encrasicolus) in subdivision 9.a West (Western Iberian waters) with advice provided in June.

The stock assessment method applied for anchovy in 9aWest and tested in a management strategy evaluation in 2023 is still relevant and no changes were proposed. A separate advice sheet should be produced by WGHANSA and advice provided in June annually. Anchovy in 9a South is now assessed using the integrated statistical catch at age model SS3. This replaces the previously used GADGET assessment that used age and length information and was used as indicator of stock development. This was applied in a category 3 approach while the new assessment is a full analytical category 1 assessment. The SS3 assessment uses catch at age data by quarter from the commercial fleet, age compositions data from three annual surveys, PELAGO and ECOCADIZ and biomass index from the ECOCADIZ- RECLUTAS which is used as an index of recruitment. SSB estimates from the triennial DEPM survey (BOCADEVA) are also included in the model. Model explorations examined a number of model and data settings including natural mortality, weight at age, fleet and survey catchability, the use of priors, selectivity and the use of blocks and recruitment assumptions. Following extensive discussions, the final assessment, reference points and short term forecasts following ICES guidelines were agreed by the group. Recommendations for further investigations are outlined in the reviewers report. Advice should be formulated by WGHANSA and provided annually in November.

General findings

Further research on stock connectivity between anchovy in 9a West (9aN, 9a CN, 9aCs) with the northern anchovy populations (in the Division 8c and with the entire stock in subarea 8) should be considered as well as, further research on the connectivity between the stock in 9a South with the populations inhabiting the Atlantic Morocco region. Further work on management strategies will be required for anchovy in division 9aS and anchovy in subarea 8. For Anchovy in division 9aS, a management strategy evaluation to assess the maximum fishing mortality that can be applied (Fcap), to ensure that in the long-term the risk of falling below Blim is <0.05, should be conducted as soon as possible. The changes made to the assessment of anchovy in subarea 8 during the benchmark could imply changes in the performance of the current management plan in terms of biological risks and expected catches. A re-evaluation of the current management plan incorporating the most recent changes in the assessment should be undertaken as soon as possible.