Genetic risk assessment model for native shellfish aquaculture

The shellfish aquaculture industry is growing, and shellfish growers have begun to cultivate native shellfish to prevent introduction of non-native species. However, cultivation of native species poses genetic risks to wild populations if farmed and wild animals interbreed. Available simulation models for assessing genetic risks of aquaculture are not well suited for shellfish life history or the complexities associated with spatial management and are often limited to one or two of at least three types of genetic risks, preventing assessment of trade-offs among risks and emergent interactions among genetic processes. We developed an open-source, individual-based simulation model for conducting genetic risk assessments of native shellfish aquaculture and demonstrated its utility in measuring a variety of genetic impacts, trade-offs among impacts, and emergent effects in Olympia Oyster (Ostrea lurida) aquaculture. The model quantifies changes in genetic diversity within and among populations, and fitness of wild populations due to farm escapees. We compared 12 scenarios, encompassing elements of commercial and restoration aquaculture under different combinations of escape rate and strength of selection. Results were generally consistent with population genetic theory, including greatest effects when both selection and escape were high and a rapid irreversible erosion of genetic differentiation among wild populations when foreign broodstock was used. We also found surprising findings, for example, a rapid decline in neutral genetic diversity caused by selection and a reduction of allelic diversity that was fastest in the farm and slowest in the local wild population under the same conditions. We suggest future directions for model uses and development and conclude by describing the management implications of our results for the cultivation of Olympia Oyster and other shellfish species.