Incorporating molecular genetic data into management decisions would provide fisheries managers with new tools to identify the magnitude of population structure, metapopulation dynamics, at risk populations, and possible genetic interactions between species, so that management strategies could be tailored to better support long-term viability of species and populations. Alewife (Alosa pseudoharengus) and Blueback Herring (Alosa aestivalis) are two closely related anadromous clupeid fishes native to the Atlantic coast of North America. Current management strategies for these two species, collectively known as river herring, take no account of stock structure or even the distinction between the two species. Using 12 neutral microsatellite loci, I examined at multiple spatial scales the patterns of population structure and genetic differentiation for river herring, with particular reference to comparisons of population structure in the U.S., where extensive stocking has occurred, and Canada, where there has been no stocking. Results suggested strong population structure within the Canadian portion of the range and weaker population structure in the U.S. portion. Highly significant genetic isolation by distance (IBD) for parts of the range unaffected by stocking provided evidence of natal homing and limited dispersal. The differing IBD results obtained in three Canadian regions may reflect differences in historical biogeographical factors and contemporary dispersal patterns among regions. Very weak differentiation and an absence of significant IBD for American stocked populations provided evidence that stocking has reduced genetic differentiation between populations in the U.S. portion of the range, except for two divergent stocked populations that appeared to have resisted homogenization. Evidence of recent population bottlenecks were identified in both U.S. and Canadian populations. The genetic structure of Blueback Herring populations appeared to be similar to that seen in Alewife. When sampled in the same river, Alewife and Blueback Herring were strongly differentiated, although hybrids of the two species were detected. Evidence of genetic impacts of stocking, regional variation in patterns of population structure and complex genetic interactions between the species suggest that current management strategies should be re-evaluated.

The relationships between watershed characteristics and stream use by spawning alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis) in the Rappahannock River drainage were identified. Trends in fish use of 72 tributaries were determined by consulting eighty-eight people from the Rappahannock River area through a questionnaire. These streams were each given an overall rank based on answers to the questionnaire. The watershed characteristics of these streams were determined from topographic maps, land use data, and digital line graphs. Trends in fish use of streams were associated with stream size, and proportions of forest, agriculture, and wetlands. No negative relationships between urbanization or presence of point-source pollution and fish use of streams were found. Forest was positively associated with stream rank, and agriculture was negatively associated with stream rank. Results indicate that, of the watershed characteristics in the Rappahannock River drainage, forest and agriculture have the strongest associations with stream use by spawning river herring. Three sites in a tributary of the Rappahannock River were studied to characterize the spawning habitat of river herring. The sites were sampled and their habitat variables were measured throughout the 1992 river herring spawning season. Densities of river herring adults, eggs, and yolk-sac larvae were highest at the upstream site. Densities of post-yolk sac larvae did not differ significantly among the sites. The upstream site differed from the downstream sites in size, vegetation, hydrology, photic zone depth, pH, and vegetation. At times, pH levels in the upstream site were within the range of lethality reported for blueback herring larvae. Relationships between habitat variables and occurrence of river herring life stages in the upstream site were identified. Effects of tidal condition, time of day, light intensity, and temperature on peaks in densities of river herring life stages in the upstream site were determined by plotting these variables with life stage densities. Trends in water temperature were positively related to peaks in densities of river herring life stages. Logistic regression was used to determine if temperature, light intensity, dissolved oxygen, velocity, depth, and secchi disc transparency predicted occurrence of river herring life stages in the upstream site. Occurrence of alewife early egg stages was positively related to dissolved oxygen and velocity. Occurrences of blueback herring adults and early eggs were positively related to water temperature. / Master of Science

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