How do shellfisheries influence genetic connectivity in metapopulations? A modeling study examining the role of lower size limits in oyster fisheries

Fisheries can potentially alter evolutionary processes such as genetic connectivity and lead to genotypic changes in stocks. Using an individual-based metapopulation genetics model, we examined the possible influence of oyster (Crassostrea virginica) fisheries on genetic connectivity. We simulated a range of realistic fishing pressures, with and without a minimum size limit (limit = 63.5 mm), over a range of fishing scenarios including single-area and stock-wide fisheries. Movement of a neutral marker gene provided an indicator of gene transfer between populations. Simulations showed that fishing may alter genetic connectivity. Increasing fishing pressure tended to decrease potential for fished populations to export genes in fisheries with and without size limits. On average, when instantaneous fishing mortality, location, and time period are held constant, fishing unrestricted by size results in a 3.5% lower allele export. Depression of the spawning potential ratio by unrestricted fishing relative to size-limited fishing argues for more conservative fishing mortality targets for unrestricted fisheries. These results demonstrate the importance of considering the influence of fisheries on source-sink dynamics in future management of marine populations.