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Many marine species are typified by a pelagic stage during which tiny larvae develop in the open ocean, where they are subject to high mortality and transport via ocean currents. For organisms with this life history, the study of their population dynamics is challenging because individuals are not directly traceable. Challenges to the study of population dynamics include the determination of source and sink populations, of connectivity among populations, of the mechanisms that drive the abundance and relatedness of recruits, and of how life-history characteristics mitigate or exacerbate the uncertainty of the ocean environment. My dissertation addressed these challenges in the Pacific black rockfish, Sebastes melanops, using a combination of standardized field sampling, population genetics, and mathematical modeling. Like other members of the rockfish genus, black rockfish are long-lived fishes that suffered severe declines in the 1980's due to overfishing. I collected adults from Oregon to British Columbia, and genotyped them at 8 microsatellite markers. I used isolation by distance theory to estimate the width of the dispersal kernel, as well as compared coalescent-migration matrices with Bayes factors. My results illustrated that over several generations, gene flow in the population occurred from south-to-north (a bearing in agreement with the direction of currents during the pelagic phase) and the mean dispersal distance (< 50 km) was smaller than might be expected based on an extensive pelagic phase of 60--80 days. This analysis was extended to examine the source populations for rockfish recruits that were collected between 2005 and 2009 from Barkley Sound (British Columbia), and my results suggested that substantial local recruitment occurred during downwelling regimes that favored the retention of larvae. However, the number of source populations for larvae was not correlated with the genetic diversity of recruits. I used cross-correlations to examine the relationships between oceanographic conditions, the abundance of recruits, and the genetic diversity of those recruits. I found that although there was a strong positive relationship between upwelling and the abundance of recruits, the effective number of breeders that contributed to each cohort was positively correlated with temperature. Finally, I utilized computer simulations to examine the conflicting predictions for multiple paternity for the effective size of a population (Ne). For long-lived species like rockfish, there were small differences in Ne between populations with multiple paternity and a monandrous mating systems, indicating that multiple paternity had little effect on the genetic patterns observed in this study. The results of my research can be applied to the conservation and management of this species across the US-Canada border, and may be useful in predicting how this species will respond to climate change.
A Dissertation submitted to the Department of Biology in partial fulfillment of the requirements for the degree of Doctor of Philosophy.
Includes bibliographical references.
Don Levitan, Professor Directing Dissertation; Jeﬀery Chanton, University Representative; Alice Winn, Committee Member; Peter Beerli, Committee Member; Brian Inouye, Committee Member.
Florida State University
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