F35%Revisited Ten Years Later

Abstract

This paper reviews the original derivation of the F35% (later F40%) harvest strategy, which consists of fishing at a rate that reduces spawning biomass per recruit to 35% (or 40%) of the unfished value, and investigates its applicability to long-lived stocks with low resiliency, such as some of the Pacific Coast rockfishes Sebastes spp. The life history parameters are unimportant (at least in deterministic calculations), but the possibility of extremely low levels of resiliency—well below the bounds of the original analysis—does render the strategy unworkable in the sense that there is no harvest rate that will obtain a large fraction of the maximum sustainable yield (MSY) across the entire range of possibilities. At low but still workable levels of resiliency, the F40% strategy results in undesirably low levels of biomass and recruitment by present-day standards. That can be cured by adopting a higher target for spawning biomass per recruit, though at some cost in yield. A purely biomass-based strategy and a modified FMSY strategy are discussed as alternatives for cases where adequate historical data are available.