When incorporating assortative mating such that individuals with more similar phenotypes are more likely to mate with each other (Fig. 8), the fitness effects of maladapted cultured-origin fish decrease because less interbreeding between cultured-origin and wild-origin fish occurs.
Analysis of the relative spawning success of aquaculture escapees (ν S ) allows us to separate the demographic effect of escapees increasing the density-dependent mortality of wild individuals (population size when ν S = 0, or no cultured-origin fish spawn) from the fitness effect that occurs when spawning of cultured-origin individuals and interbreeding with the wild population occurs (Fig. 5).
Finally, we explore the effect of the relative cultured-origin spawning success parameter ν S to determine the potential efficacy of partial (0 < ν S < 1) or full (ν S = 0) sterilization.
Therefore, the postselection population density is (5) Given these parameters, the mean fitness of the wild spawner population is (6) Before reproduction, we combine the wild-origin and cultured-origin populations to form the new wild spawner population.
In many cases, cultivation programs occur in the same location as wild conspecifics, which can lead to large escape of cultured-origin individuals that interact and interbreed with wild populations.
This effect declines rapidly and nonlinearly with decreasing spawning success of cultured-origin individuals, which could represent increasingly effective sterilization or reduced reproductive success due to nongenetic effects of rearing in the cultured environment.
If escape occurs before natural selection, an intermediate minimum in fitness and population size, and an intermediate maximum in recovery time, can occur at intermediate θ C. In this case, selection can purge extremely maladapted cultured-origin individuals (low θ C ) before they reproduce and interbreed with wild individuals.
When the cultured-origin individuals are maladapted enough to substantially reduce wild fitness (θ C <∼ 0.5, Fig. 5B), the fitness effects of aquaculture escapees can cause a decline in population size (Fig. 5A) and increase in recovery time (Fig. 5C) as much or greater than that due to their demographic effect.
This greater decline in fitness is realized through both a deeper fitness trough and a fitness trough shifted to the left, such that a greater degree of maladaptation in the cultured population is necessary for natural selection to effectively purge cultured-origin individuals.
