Fish Population Dynamic and Stock Assessment

1.4.6. Production functions

The relationship between average production and fishing effort is known as the production function. Production functions are the basis for certain important concepts like: maximum sustainable yield. In addition, the term stock level is employed as a biological reference for determining resource status relative to the biomass that would on average support the sustainable yield. Recent average yield also is reported in order to allow comparison of the current situation to the sustainable yield.

Many other reference levels are used as benchmarks for guiding management decisions. A number of these are expressed as fishing mortality rate levels that would achieve specific results from the average recruit to the fishery if the stock were subjected to fishing at those rates indefinitely. Some of these benchmarks are used to index potential fishery production, and others are used to index potential reproductive output. F_max is the fishing mortality rate that maximizes the yield obtained from the average recruit. Growth overfishing occurs over the range of fishing mortality, at which the losses in weight from total mortality exceed the gain in weight due to growth. This range is defined as beyond F_max.