Analysis of Fmsy in light of life-history traits-Effects on its proxies and length-based indicators

Equilibrium 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 (F-msy), its selected proxies (F-0.1, F-40%, F-40%SSB and F-max) and mean length at F-msy (L-msy) were estimated. Next, linear models combining the estimated F-msy and L-msy with the traits were fitted (R-2 > .95). Almost all of the LHTs were statistically significant, and the largest effect on F-msy was from steepness, while natural mortality and growth rate had smaller effects. In the case of L-msy, however, the largest effect in the fitted model was from the growth rate, while steepness influenced L-msy only slightly. The F-msy proxies were evaluated, and F-40%SSB appeared to be a generally conservative F-msy proxy, while F-max always overestimated F-msy, generally to a large extent. F-0.1 and F-40% may be used as F-msy proxies or conservative proxies mainly for steepness values of 0.6 and higher; for lower steepness, they may markedly overestimate F-msy. The ratio of biomass at F-msy to 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 to L-msy for evaluating stock status should be done with caution, especially for species with a high growth rate.