Characterizing American Shad Spawning Habitat in the Upper Roanoke River Basin, Virginia

Abstract

Populations of American shad (Alosa sapidissima) have declined from historical levels due to overfishing, decreased water quality and habitat losses including those due to dam construction. One approach for restoring these populations is to identify suitable habitat upstream of dams that could be restored through dam removal or by providing fish passage. The goal of this research is to identify and characterize potential spawning habitat for American shad in the upper Roanoke River basin of Virginia, above Kerr Reservoir. Five mainstem rivers that are upstream of the Roanoke Rapids, Gaston, and Kerr dams (Big Otter, Staunton, Banister, Dan, Hyco) were the focus of this research. Roanoke Rapids Dam is the first obstruction to American shad spawning migration in the Roanoke River basin, and just completed the FERC (Federal Energy Regulatory Commission) relicensing process in 2004. One of the provisions of the new license is to evaluate a trap and transport program for spawning American shad. Characterizing the habitat above the dam, in terms of suitability, is an important step in predicting the benefits of fish passage.

A detailed physical habitat assessment, including monthly water quality monitoring, indicated that the Banister and Hyco rivers consistently had lower dissolved oxygen concentrations and may provide lower quality habitat for American shad compared to the other rivers. However, according to the current published Habitat Suitability Index (HSI) model, which incorporates surface water temperature and current velocity as criteria for suitable habitat, the five rivers appear to contain suitable habitat with HSI values ranging from 0.83 to 1.00 during May. I constructed a modified HSI model with surface water temperature and current velocity, as well as dissolved oxygen, pH and a component for substrate composition. The modified model suggested that the Big Otter and Staunton rivers would provide the highest quality spawning habitat for American shad because of the presence of gravel, cobble and bedrock substrates. Larger substrates have been suggested to be preferred over smaller substrates by spawning adult American shad in the Neuse River, NC.

Egg incubation experiments were conducted during the American shad spawning season, from mid-April to the end of May 2004, throughout the basin. Hatching success from incubation experiments was relatively high (69-94 percent). No significant differences (p<0.05) among incubation sites were found in terms of hatching success, which suggests that water quality throughout the basin is suitable for egg development.

The combination of field data and habitat suitability modeling used to predict habitat quality was an efficient approach for assessing habitat and could be used by planners and managers working to restore American shad populations in other river systems. Results from the physical habitat assessment, the habitat suitability modeling and the egg incubation results suggest that a trap and transport program should be successful for spawning American shad in the Roanoke basin.