Genetic Difference between Wild and Released Individuals and the Resource Enhancement Effect of Stocking: A Theoretical Analysis

Abstract

Stocking of natural populations with fish fry, which are artificially reared or taken from other populations, is performed in order to enhance fishing productivity. For several reasons, artificially reared or foreign fry are sometimes expected to have a less adaptive genetic nature than indigenous ones. In such cases, natural reproduction of the released individuals has not only a positive effect of increase in the population egg production, but also a negative effect of genetic deterioration. In this paper, I analyze the effect of the maladaptive genetic nature of released individuals on resource enhancement by using simple mathematical models, and show that the total effect of the natural reproduction of maladaptive individuals is negative. Thus, low fecundity and selective harvesting of the released individuals are desirable not only from the viewpoint of genetic conservation, but also from that of resource enhancement. I also analyze the effect of the ratio of sexes released, and show that the enhancement effect is high and the degree of genetic deterioration is low if it is female biased.