Bmsy

BMSY, short for biomass at maximum sustainable yield, is a fisheries management concept describing the level of population biomass that can support the maximum long‑term catch (MSY) under a stock’s growth dynamics and natural mortality. At BMSY, fishing mortality is typically FMSY, the rate of fishing that yields MSY. Thus, BMSY and FMSY are linked by the stock’s growth function: allowing harvest at FMSY tends to maintain biomass around BMSY on average.

Estimation of BMSY is indirect. It is inferred from stock assessment models that fit catch history, survey indices, age structure, and recruitment data. Common model families, such as the Schaefer model or the Pella–Tomlinson model, yield BMSY as a function of parameters like carrying capacity and intrinsic growth rate. The precise value of BMSY varies among species and stocks.

Usage in management involves using BMSY as a reference point to guide harvest decisions and to define targets and limits. Management plans often relate BMSY to the unfished biomass B0, with BMSY typically representing a fraction of B0 (for example, in the simple Schaefer model BMSY equals B0/2). In practice, BMSY serves alongside other reference points such as Blim (biomass limit) and Btrigger to determine when actions are needed to reduce fishing pressure or implement conservation measures.

Uncertainty is inherent in BMSY estimates due to model structure, data limitations, and natural variability. Management commonly adopts precautionary buffers and uses ranges or confidence intervals around BMSY estimates.

See also: MSY, FMSY, Blim, Btrigger, reference points.