The stock-recruitment (S/R) relationship is fundamental to the management of natural resources, especially fish and shellfish stocks. The nature of this relationship is used to determine to what extent a population may be harvested by either commercial or sport fisheries.
The S/R relationship is normally presented graphically as a scatter plot with the number of females in the spawning stock on the x-axis and the number of recruits on the y-axis. The spawning stock is defined as the number of female organisms in the population of reproductive age and able to reproduce in any one year. The recruits are defined as those young who survive to either maturity, or to be captured by the fishery.
The replacement line is where stock = recruits. Any recruits above this line are considered to be “in excess” of that required to maintain the population, and can therefore be harvested without impact to the population.