FMSY

F-MSY is the rate of fishing mortality that, held constant, drives a stock to the biomass producing maximum sustainable yield. It is the most common harvest-control target in modern assessments: keep realized F at or below F-MSY and biomass at or above B-MSY. ICES, NOAA, and the tuna RFMOs frame their advice around F-MSY proxies because true F-MSY needs a reliable stock-recruit relationship, which is rarely known with precision. When data are thin, managers substitute proxies such as F-40% spawning-potential ratio.