Recruitment

Recruitment is the addition of young fish to the harvestable or spawning portion of a stock, the inflow that replaces losses to mortality. It is measured as the number of fish surviving to a defined recruitment age or size, and it is the most variable term in population dynamics, often swinging an order of magnitude between strong and weak year-classes driven by larval survival and the environment. Stock-recruitment models such as Beverton-Holt, where recruitment rises asymptotically with spawning biomass, and Ricker, where it peaks then declines, link spawners to recruits. Recruitment variability is why a single strong year-class can carry a fishery for years.