Fmsy

FMSY, or fishing mortality at maximum sustainable yield, is the rate of fishing at which a fish stock’s long-term average catch is maximized under a specified stock-recruitment relationship. It is a stock-specific reference point used in fisheries management to guide harvest levels and protect the population over time. In practice, FMSY is not a fixed universal number; it depends on the biological productivity, growth, and recruitment of the stock and can vary with age structure and environmental conditions.

Estimation of FMSY involves stock assessments that use mathematical models to relate fishing mortality, stock size, and recruitment. Common approaches include age-structured models, surplus production models, and integrated assessments that combine catch data with biological information. FMSY is derived as the fishing mortality rate that yields MSY under the model. For data-poor stocks, managers often use proxy reference points that approximate FMSY, such as targets based on biomass levels (for example, a biomass corresponding to a fraction of unfished biomass) or policy-defined benchmarks.

In management practice, FMSY serves as a benchmark for sustainable harvest. It is connected to BMSY, the biomass level that supports MSY. When fishing mortality is at FMSY, the stock is expected to hover near BMSY over the long term. If fishing pressure exceeds FMSY, the stock tends to decline and may become overfished; if it remains below FMSY, biomass can recover toward carrying capacity. Because of uncertainties in recruitment, environmental variability, and model assumptions, many regulations incorporate precautionary margins and adaptive management around FMSY.