Publication Abstract

An Evaluation Of The Implicit Management Procedure For Some ICES Roundfish Stocks

An Evaluation Of The Implicit Management Procedure For Some ICES Roundfish Stocks.

L.T. Kell, G. Pilling, G. Kirkwood, M. Pastoors, B. Mesnil, K. Korsbrekke, P. Abaunza, R. Aps, A. Biseau, P. Kunzlik, A. Laurec, C. Needle, B. Roel and C. Ulrich

Using simulation, this study examined the performance of the management procedure implicit within ICES advice for some of the main roundfish stocks. An integrated modelling approach was used, which modelled both the ‘real’ and observed systems and the interactions between all system components. The modelling framework therefore allowed evaluation of the robustness of management strategies to both the intrinsic properties of the systems, and the ability to observe, monitor, assess and control them. Strategies were evaluated in terms of level of risk (measured as the probability of spawning stock biomass falling below the biomass limit reference level for the stock) and yield.

The simulation approach used provides a powerful tool for the examination of the performance of candidate management strategies. It shows that better management is not necessarily going to be achieved by improving the assessment, since even with a perfect assessment (where the simulated working group knew stock status perfectly) stocks may crash at fishing levels that standard stochastic projections would suggest were safe. Also explicitly modelling the assessment process can result in quite different outcomes than those predicted by the simple projection traditionally used by stock assessment working groups. This is because the simple projection assumes that the status of the stock in the current year is known without error and that the target fishing mortality can be achieved without error. However, in practice the assessment is based on last years data and the effect of any management measure on SSB is only manifest much later, following the implementation of the quota, at the end of the following year.

The choice of target and threshold fishing mortality levels and minimum stock levels results from ICES interpretation of the precautionary approach. This lead to the definition of fishing mortality and biomass reference points that are intended to prevent over-fishing and to trigger recovery measures when a stock is overfished. Although fishing mortality and biomass reference points were originally intended to be independent, a fishing mortality level implies a corresponding biomass level. It was also shown that the choice of biomass and target reference points have not always been made consistently

Reference:

L.T. Kell, G. Pilling, G. Kirkwood, M. Pastoors, B. Mesnil, K. Korsbrekke, P. Abaunza, R. Aps, A. Biseau, P. Kunzlik, A. Laurec, C. Needle, B. Roel and C. Ulrich (2005). An Evaluation Of The Implicit Management Procedure For Some ICES Roundfish Stocks. ICES Journal of Marine Science, 62(4): 750-759.

L.T. Kell*, G. Pilling*, G. Kirkwood, M. Pastoors, B. Mesnil, K. Korsbrekke, P. Abaunza, R. Aps, A. Biseau, P. Kunzlik, A. Laurec, C. Needle, B. Roel* and C. Ulrich

ICES Journal of Marine Science, 62(4): 750-759