Patterns and Processes of Fish Dispersal and Settlement along the Oregon Coast

Graduation date: 2017Access restricted to the OSU Community, at author's request, from January 10, 2017 - January 10, 2018Most benthic marine organisms have a bipartite life with an early pelagic stage that enables dispersal of offspring, connecting spatially separated populations, and a late stage where individuals reside in a benthic habitat. Settlement of pelagic offspring to bottom associated substrates is the process that connects the two life history phases. Thus, settlement is fundamental to the recruitment of individuals to the adult benthic population. Together with collaborators, in my first data chapter (Chapter 2) I evaluated patterns and processes of temperate fish dispersal and settlement to nearshore habitats of central and southern Oregon (northwest U.S.) over 6 yrs, and related these patterns to oceanographic conditions. Our results revealed that settlement of the five focal taxa peaked at different times of the sampling season and exhibited varying degrees of episodic timing. Settlement of most species tended to peak during upwelling relaxation events, although most trends were statistically insignificant. Size-at-settlement varied among taxa and within taxa over time, but in no case did we find a significant correlation between size and water temperature, likely due to multiple factors (growth rate, pelagic duration) contributing to size-at-settlement. Settlement of splitnose rockfish (Sebastes diploproa) was the most episodic of all the taxa analyzed in this study.\ud Chapter 3 reports on the results of a genetic kinship analysis conducted on individuals of a very large pulse of splitnose rockfish that settled during a single sampling event in 2013. Our results revealed that at least 11.6% of the settlers were siblings, indicating that they remained aggregated throughout their 4-6 mo dispersal phase. This is the first demonstration of such long term aggregation by early stages in a complex oceanographic environment and has major implications for our understanding of the dispersal process. Together, the two data chapters in this thesis provide new information on settlement patterns and processes for fishes along the coast of Oregon. The settlement data are important to monitoring efforts in local marine reserves and enable comparisons over large spatial scales with similar studies conducted along the California coast. Our demonstration that offspring can remain aggregated throughout their entire dispersal phase reveals an underestimated layer of complexity in larval dispersal, building fundamental knowledge towards a more complete understanding of marine dispersal and its influence on population genetics and population regulation