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Rapport2024

Workshop on the calculation and evaluation of new reference points for category 1–2 stocks (WKNEWREF)

Jacobsen, Jan Arge; Aristegui-Ezquibela, Mikel; Aune, Magnus; et al.

Sammanfattning

WKNEWREF is the third workshop of a series of meetings about reference points for category 1 and category 2 stocks being WKREF1 and WKREF2 the preceding ones. The goal of WKNEWREF was to put the recommendations of WKREF2 into practice to identify empirically the strengths and weaknesses of proposed reference points. Ultimately, WKNEWREF should propose alternative definitions or methods to calculate the reference points in the current ICES framework and investigate the use of an Ftarget below FMSY in the ICES advice rule (AR).
The workshop had two sets of terms of reference, the first one consisted of the estimation of the stock–recruitment relationship and a set of reference points in a representative group of category 1 and 2 stocks. The second one consisted of the identification of the issues encountered when fitting the stock–recruitment relationship and the strengths and weaknesses of estimated refer-ence points. Reference points were calculated for more than 20 stocks.
WKNEWREF made a series of recommendations based on the conducted analysis:
• Allee effect: The presence of the Allee effect should be evaluated when defining Blim, par-ticularly when the stock has experienced periods of low stock spawning biomass. Blim should always be set above the Allee effect threshold if it exists and can be estimated.
• Regime shifts: Robustness of the ICES AR to changing productivity scenarios should be tested. The research on factors determining the productivity of stocks should continue and on the development of models that account for changes in productivity without the need for truncating time-series.
• Stock–recruitment relationship: The current guidelines to define the stock–recruitment re-lationship should be revised to make them more precise. The sensitivity of the parame-ters to historical data points should be evaluated before selecting the year range to use for the calculation of reference points.
• Blim: Several recommendations in relation to Blim were made. First, quantitative criteria to assign the stock type for the definition of Blim should be defined. Second, for type 5 stocks, Bloss should be replaced by the empirical Blim. Third, when defining Blim the corresponding B0 percentage should be calculated as a sense checking. The guidelines should include the option of using %B0 to define Blim for model ensembles and production models. Fur-thermore, when the Blim derived from the current six stock types is not considered rea-sonable, defining it as %B0 may be considered. In such cases, percentages used in the literature and obtained in the ICES database for different families should be considered as a reference value.
• FMSY and Fpa: FMSY and Fpa should be calculated including the time-lag between manage-ment and advice. The calculation of Fpa should incorporate the advice rule. An accessible tool to allow the estimation of FMSY and Fpa including the time-lag should be developed.
• MSY Btrigger: The system was not very sensitive to the MSY Btrigger value and no particular recommendations were made.
• Ftarget: The workshop found benefits in exploiting the stock at exploitation levels below FMSY and difficulty in defining an alternative fishing mortality reference point that is equivalent among stocks. The main drawback of reducing the target fishing mortality would be the short-term losses in catches.

In the short term, future work should focus on defining MSY Btrigger and Ftarget and developing a simulation tool that can incorporate the recommendations made. In the longer term, the integra-tion of changes in productivity into the calculation of reference points and the advice rule should be studied.

Publicerad i

ICES scientific reports
2024, nummer: 6:100
Utgivare: International Council for the Exploration of the Sea

SLU författare

UKÄ forskningsämne

Fisk- och akvakulturforskning

Publikationens identifierare

  • DOI: https://doi.org/10.17895/ices.pub.27905664

Permanent länk till denna sida (URI)

https://res.slu.se/id/publ/139436