The amount of yield in weight that can be removed from a population of fish without leading to biomass increase or decline. When the population net productivity is high (e.g. at medium levels of, close to maximum sustainable yield, MSY), the replacement yield will also be high. Conversely, when the productivity is low (e.g. when the population is underexploited or overexploited), the replacement yield will be low. In either case, if the actual yield taken is equal to the replacement yield, then the biomass will not change from one year to the next.