Report of the Workshop for management strategy evaluation for Norway Pout (WKNPOUT)
The ICES Workshop for management strategy evaluation for Norway Pout (WKNPOUT) took place 26–28 February 2018 at ICES Headquarter chaired by Andrés Uriarte, Spain, with the assistance of ICES Secretariat. 12 participants, both scientific experts and stakeholders, from Denmark and Norway, attended the meeting. The group addressed the special request from the European Union and Norway to advise on the long-term management strategies of Norway Pout in ICES Subarea 4 (North Sea) and ICES Division 3.a (Skagerrak-Kattegat). The proposed management strategy is based on the ICES escapement strategy with the aim of achieving a high probability of having the minimum SSB required to produce MSY (Blim) surviving to the following year. ICES was requested to evaluate:
- Whether a management strategy is precautionary if the TAC is constrained with a lower bound in the range of 20 000 tonnes to 40 000 tonnes and an upper bound in the range of 150 000 tonnes to 250 000 tonnes, or another range suggested by ICES.
- Whether such a strategy would be precautionary if the TAC constraints referred to in paragraph 1 are overridden by a constraint on the maximum value of fishing mortality (Fcap), and whether the application of the Fcap would allow a precautionary strategy with a higher minimum TAC than if the Fcap was not applied.
- Whether a provision to override the minimum value of the TAC when the stock is forecast to be below some threshold value would allow a precautionary strategy with a higher minimum TAC than if the escape-clause was not included, and whether such a provision would provide any additional benefit to the inclusion of an Fcap as referred to in paragraph 2.
The alternative management procedures were tested in the framework of a manage-ment strategy evaluation (MSE) set up according to the assessment model SESAM adopted for Norway pout in the 2016 benchmark. One thousand simulations (replicates) were projected over 20 years for each of the different harvest control rules. Each replicate begins in the 2018 TAC year which starts in quarter 4 of calendar year 2017. Each replicate randomly draws a true state of the system (starting population, age and quarterly fishing patterns and series of past recruitments) from the joint distribution estimated by the last stock assessment. This is taken as the approach best reflecting the uncertainties in the SESAM assessment. An alternative reducing the uncertainty in the initial stock numbers, recruitment and exploitation pattern at the median estimate from the last assessment was also tested. The simulations were conditioned by a maximum realized level of fishing mortality the fishery can exert (assumed at 0.89; Fhistorical), which means that the full TAC will not be taken if the required F exceeds this value.
First the group tested whether the current ICES procedure for providing TAC advice for Norway Pout, based on an escapement strategy (the default method), was precau-tionary. Results showed that it is not precautionary (as tested with unconstrained levels of fishing mortality), because the probability of SSB falling below Blim is higher than 5%. This is probably linked to cases of very high TAC and F when very high recruit-ments occur, in association with observation errors in the assessment. This called for modifying the default escapement strategy either by setting an upper F (Fcap) or including conditions on TACmin/ TACmax as explored here.
Published under the auspices of the following ICES Steering Group or Committee