WORKSHOP OF FISHERIES MANAGEMENT REFERENCE POINTS IN A CHANGING ENVIRONMENT (WKRPCHANGE, OUTPUTS FROM 2020 MEETING)

WKRPChange was tasked with examining how ICES handles the estimation of target and limit reference points in the face of changing environmental conditions. In particular, the meeting participants were asked to review the robustness of the current ICES procedures and to suggest specific improvements that could be made, especially relating to changes in stock productivity arising from environmental conditions, species interactions, and density-dependent effects. Part of the work involved reviewing the basis of the ICES reference points and contrasting the ICES procedures with those in the USA and Canada, and part on providing specific guidance for future reference point estimation within ICES.

One common approach to changing environmental conditions is to truncate data series. WKRPChange agreed that this may be necessary in some cases, but several studies were presented showing that the estimation of reference points becomes unreliable (both noisy and potentially biased) as the time series is reduced, and therefore recommended that modelling the specific process involved is generally a better approach than truncation. The meeting noted several examples within the current ICES management system for which reference points are allowed to vary (e.g. F in the case of NEA cod, Blim in the case of Iberian Sardine) according the prevailing conditions. WKRPChange noted that this was only required if conditions were expected to change significantly over the lifespan of the reference points, and that where it was implemented the status determination (the “traffic lights”) should be made accordingly.

The key recommendation of WKRPChange is consistent with the conclusions of WKGMSE2, namely that a scoping exercise should be undertaken for each stock to identify any key drivers. Where there is good evidence for ecosystem-driven changes in stock productivity that process should be accounted for in setting reference points. The meeting highlighted that reference points have a finite lifespan, generally related to the benchmark cycle, and the estimation of the reference point should predominantly take into account processes likely to be important over that lifespan. WKRChange noted that many ICES stocks are managed by Harvest Controls which are evaluated through a MSE process. In this case there is considerable scope for including such environmentally driven processes in the Operating Model. However, many stocks are managed through the standard ICES HCR with reference points derived through the EqSim program. There is therefore a specific recommendation that the possibility to include density-dependent
growth be incorporated into EqSim, to allow more realism to be included in the estimation of reference points where the evidence indicates that this is important within the reference point life span. The meeting also highlighted the recent work at WKRISH 6, which gave scope to “fine tune” the F_target to account for small changes in environmental drivers without requiring full reestimation of the reference points.