Effects of pumped storage project operations on the spawning success of centrarchid fishes in Leesville Lake, Virginia
Research was initiated in the spring of 1972 to evaluate the effects of the Smith Mountain Pumped Storage Project on the spawning success of centrarchid fishes in the lower impoundment, Leesville Lake.
Hydroelectric power generation operations at the Smith Mountain Dam power plant create high water velocities with daily flow reversals, and water level and temperature fluctuations in Leesville Lake. Water levels in Leesville fluctuate as much as 3.5 m (11 ft) per day and 4 m (13 ft) per week during spawning periods of centrarchid fishes. In addition, daily intrusions of subsurface water from Smith Mountain Lake into Leesville Lake during periods of power generation average less than 20 C in temperature. At night and on weekends, surface waters from Leesville Lake are pumped back to Smith Mountain Lake. These project operations create three fluctuating, relatively unstable sections in Leesville Lake; a cool upper reservoir zone, a mid reservoir temperature mixing zone, and a warmer lower reservoir zone.
Centrarchid fishes were collected from the three reservoir zones in Leesville Lake and gonads were examined. Generally, gonadal maturation and the presence of fish in spawning condition occurred earliest in the warmer lower zone, later in the mid reservoir, and last in the cooler upper zone of Leesville Lake during 1972 and 1974.
During 1974, trained divers located and inspected 2010 centrarchid fish spawning nests in Leesville Lake. Based on a constant unit of diving effort, 40 percent of nests occurred in lower Leesville, 57 percent in mid, and about 3 percent in the upper reservoir zone. High water velocities restricted spawning activity in the mid and upper reservoir zones almost entirely to cove areas. Water velocities in lower Leesville had negligible effects on the distribution of spawning activity. A stepwise regression model indicated that water velocities during power generation at Smith Mountain Dam was the single most important factor affecting the distribution of spawning nests in the main lake.
Vertical distribution of centrarchid fish spawning nests suggested that adjustment to the spawning depth had occurred in response to the fluctuation in water levels. Nearly 40 percent of all spawning nests in Leesville Lake were located 0.3 to 1.5 m below minimum pool elevation or about 4. 5 m below maximum pool level.
Laboratory and field studies were conducted to evaluate hatching success of bluegill (Lepomis macrochirus) eggs under controlled water temperatures and exposures to air. Average hatching success increased as hatching temperatures increased from 16 to 28 C. Hatching success of naturally spawned bluegill eggs exposed during night and daytime hours in natural spawning nests in Leesville Lake decreased with increased exposure to air.
SUCCESS, a computer-implemented mathematical model using data generated in this study, indicated that the average spawning success of bluegill would be about two times higher in the lower zone than in upper Leesville Lake. Predicted estimates of spawning success of bluegill for the entire reservoir were about 31 percent. Based on the current levels of exploitation, natural spawning success of largemouth bass and bluegill in Leesville Lake appears adequate to maintain the densities of these centrarchid fish stocks.