Analysis ofFmsyin light of life‐history traits—Effects on its proxies and length‐based indicators

Abstract

AbstractEquilibrium yields and biomasses in relation to fishing mortality were generated for a wide range of life‐history traits (LHTs), which included growth parameters, natural mortality, maturity, selectivity and steepness of the Beverton and Holt stock–recruitment relationship. For each combination of LHTs, the fishing mortality expected to produce maximum sustainable yield (Fmsy), its selected proxies (F0.1,F40%,F40%SSBandFmax) and mean length atFmsy(Lmsy) were estimated. Next, linear models combining the estimatedFmsyandLmsywith the traits were fitted (R2 > .95). Almost all of the LHTs were statistically significant, and the largest effect onFmsywas from steepness, while natural mortality and growth rate had smaller effects. In the case ofLmsy, however, the largest effect in the fitted model was from the growth rate, while steepness influencedLmsyonly slightly. TheFmsyproxies were evaluated, andF40%SSBappeared to be a generally conservativeFmsyproxy, whileFmaxalways overestimatedFmsy, generally to a large extent.F0.1andF40%may be used asFmsyproxies or conservative proxies mainly for steepness values of 0.6 and higher; for lower steepness, they may markedly overestimateFmsy. The ratio of biomass atFmsyto virgin biomass was on average 0.34, and for a steepness of 0.9, some values were lower than 0.2. The analysis indicates that the use of the mean length of a catch in relation toLmsyfor evaluating stock status should be done with caution, especially for species with a high growth rate.