stockrecruitment

Stock recruitment is a concept in population dynamics and fisheries science that describes the relationship between the size of the breeding or spawning stock and the number of young individuals that survive to join the population in the next generation. In practice, recruitment is the inflow of new individuals into the exploitable stock, while the stock refers to the mature, breeding portion of the population. The basic premise is that larger parental stocks generally produce more recruits, but the relationship is modulated by density dependence and environmental conditions.

The most common models describing stock-recruitment relationships include the Beverton-Holt model and the Ricker model. The Beverton-Holt form expresses recruitment R as a function of stock S as R = (aS) / (1 + bS), yielding a saturating curve where recruitment increases with stock but levels off at high densities. The Ricker model, R = aS e^{-bS}, allows for overcompensation, where recruitment initially rises with stock but declines if the stock becomes too large due to factors such as competition or cannibalism. Other formulations assume a linear or nonstationary relationship and incorporate stochastic elements to reflect environmental variability.

In management, stock-recruitment relationships are used in stock assessments to forecast recruitment under different spawning stock sizes and to set harvest policies that aim to sustain yields. Limitations include substantial year-to-year variability, nonstationarity over time, and sensitivity to measurement error in stock size and recruitment. Consequently, managers often treat the relationship as one component among several in precautionary decision-making.