Survey-based estimates of Fmsy and its proxies

Abstract

A method to estimate Fmsy and its proxies based on survey indices of stock size and recruitment was developed and tested on simulated data sets and on five real stocks in the Baltic and Celtic Sea. The considered stocks were stocks with full analytical assessments (to compare the Fmsy estimates of the method with available analytical estimates), two stocks with assessments considered indicative of trends only, and one fully data-limited stock. The method combined yield-per-recruit (YPR) and spawning stock-per-recruit (SPR) analysis with survey-based stock-recruitment relationships. Various levels of uncertainty in the survey data and stock-recruitment relationships were considered in the tests. Tests on simulated data sets showed very low differences (no more than 0.01 for medians of estimates) between the generated Fmsy and F40%SSB (F for which the stock is reduced to 40% of the unfished stock) and respective estimates from survey-based methods. For sprat and herring in the Baltic Sea, the Fmsy estimates using the proposed method and survey data were comparable to the Fmsy based on analytical stock assessments. The method provided closer estimates of Fmsy than Fmsy proxies such as F0.1, F40%, and the Fmax from YPR and SPR analysis.