Thesis

The genetic diversity and population structure of barred sand bass, Paralabrax nebulifer

Fishery management relies on aspects of the life history of a fished species to implement effective management strategies. One aspect that has been underutilized is molecular markers. The addition of these methods can lead to a better understanding of a fishery stock and thus better management strategies. This study looks at barred sand bass (commonly, sand bass), Paralabrax nebulifer, a commonly fished species in southern California and Baja California, Mexico. Sand bass form large spawning aggregations in the summer months of June-August, which makes them highly susceptible to overfishing. In the last decade, populations of sand bass in southern California have experienced a severe decline in numbers and subsequently the recreational fishery has been seriously impacted. Large population declines, such as a fishery decline, can lead to a decrease in genetic diversity and potentially a genetic bottleneck. This is a concern for barred sand bass populations; however, the population structure and genetic diversity of barred sand bass populations was previously unknown. This study looks at both aspects using the d-loop region of the mitochondrial DNA and microsatellite markers for populations throughout California and Mexico. Samples of barred sand bass were collected between 1997 and 1999 and from 2010 to 2013. DNA was extracted and amplified using PCR for the mitochondrial DNA control region and for microsatellite primers developed for barred sand bass. Microsatellite primers were designed and tested for this study. Both markers show a high degree of genetic diversity indicating one large, panmictic population. However, there is some genetic structuring around the San Quintin upwelling zone in Baja California, Mexico. This upwelling zone is likely an oceanographic barrier to larval transport; however it is an incomplete barrier as evidenced by the high degree of gene flow between the two populations. There is no evidence of a genetic bottleneck; however, it may be that not enough time has passed to reflect a bottleneck due to the fishery decline. This study provides a base line for the genetic diversity of barred sand bass and can be used to monitor barred sand bass in the future.

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