Surplus Production Models
Surplus production models are the simplest analytical method available that provides for a full žsh stock assessment. Described in the 1950s (Schaefer, 1954, 1957), they are relatively simple to apply, partly because they pool the overall effects of recruitment, growth, and mortality (all aspects of production) into a single production function. The stock is considered solely as undifferentiated biomass; that is, age and size structure, along with sexual and other differences, are ignored. The minimum data needed to estimate parameters for such models are time series of an index of relative abundance and of associated catch data. The index of stock abundance is most often catch-per-unit-effort, but could be some žshery-independent abundance index (e.g., from trawl surveys, acoustic surveys), or both could be used.