Understanding connectivity among exploited populations is critical to their sustainable management and long-term viability. In the marine environment, estimates of connectivity often rely on the use of genetic markers, as dispersal primarily occurs during a planktonic larval phase which is difficult to track using direct methods. In this thesis, we investigated the population genetic structure of the most valuable commercially harvested species on the west coast of the United States, the Dungeness crab (Cancer magister). We utilized both population- and individual-​based genetic analyses to establish baseline knowledge of genetic connectivity of Dungeness crab throughout ~1,200 km of the California Current System (CCS) in 2012, and tested for inter-annual variability in our estimates by sampling again in 2014. In 2012, we observed a pattern of isolation by distance despite there being little genetic population structure throughout our study range. In addition, several sites had significant evidence of kin aggregation, which was correlated with genetic differentiation as measured by pairwise FST. In 2014, pairwise FST estimates were noticeably lower, there was no spatial autocorrelation​, and fewer sights had significant evidence of kin aggregation. We attributed these findings to increased migrant exchange during potential larval dispersal years, which was mediated by variation in physical oceanographic conditions (i.e. Pacific Decadal Oscillation phase, timing of the spring transition, amount of upwelling during the spring and summer). Dispersal trajectory, and thus gene flow, is likely influenced by variation in physical oceanographic conditions, thereby affecting genetic population structure. Estimates of effective population size (NE) indicated that NE was large in both 2012 and 2014, but we were unable to discern any change between years. Together, these findings suggest that Dungeness crab in the CCS may constitute a single evolutionary population, though geographically limited dispersal results in isolation by distance. We also evaluated genetic connectivity among Dungeness crab inhabiting a partially enclosed water body, Puget Sound, in comparison to those residing in the coastal ocean. With the exception of Hood Canal, we observed genetic homogeneity within both Puget Sound and coastal Washington. Genetic differentiation between Puget Sound and coastal Washington was variable among sites, therefore genetic connectivity is stronger within either area than between them. Overall, our results suggest that Dungeness crab exemplify characteristics of a ‘high gene flow’ species, despite evidence supporting geographically limited gene flow. Our findings did not indicate that altering the management strategy to reflect discrete genetic subunits or conversation needs (i.e. low genetic diversity) is necessary at this time. In addition, our findings highlight the need for future research to investigate demographic processes that influence gene flow (i.e. dispersal trajectory).

Jackson, Tyler M.
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A thesis investigating the population genetic structure of the Dungeness crab (Cancer magister).
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Entry Date: 
Tuesday, June 13, 2017
100 pp
Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon
Master of Science
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