Habitat relationships for alewives and blueback herring in a Virginia stream

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.