Skip to Content

INFLUENCE OF WATER LEVELS AND HABITAT MANIPULATIONS ON FISH RECRUITMENT IN NORMANDY RESERVOIR

Spring water levels account for much of the variation seen in spawning success of fishes in Normandy Reservoir. The years of 1992, 1993, and 1995 and 1997 were characterized by the following:

  • low spring water levels, often not attaining full pool until April 30
  • low crappie, white bass, and gizzard shad reproduction
  • delayed spawning by largemouth bass and threadfin shad
  • slow growth rates, poor survival, and lower abundance of young-of year largemouth bass

In contrast, spring water levels in 1994 and 1996 exceeded full pool as early as March 27, remained at or above full pool most of the spring, and fish dynamics were characterized by the following:

  • high crappie, white bass, and gizzard shad reproduction
  • natural reproduction by saugeyes
  • earlier initiation and longer duration of largemouth bass and threadfin shad
  • spawning periods
  • formation of a bimodal length-distribution of fast-growing young-of-year
  • largemouth bass
  • high survival rates and abundance of young-of-year largemouth bass

The Normandy Project has examined many different aspects of the fish community in the reservoir. Other pertinent findings of this project include:

  • Electrophoretic analysis of Stizostedion spp. confirmed that stocked saugeyes were reproducing in Normandy Reservoir, both with other saugeyes and with walleyes. Reproduction of saugeyes in Normandy Reservoir has compromised the genetic integrity of walleyes in the reservoir, placed downstream parental stocks at risk, and precluded the control of Stizostedion population densities.

  • year-class strength of largemouth bass was fixed in late summer every year.

  • neuston net sampling of larval fishes was effective in predicting subsequent year-class strength of crappies and white bass. This sampling method could allow managers to determine when poor year classes of these species are produced and take appropriate remedial action.

  • Spotted bass and largemouth bass were spatially segregated in Normandy Reservoir. Young-of-year largemouth bass were usually more abundant in the lower basin; young-of-year spotted bass were more evenly distributed. Catch of age-1 and older largemouth bass was highest in an embayment off the lower basin; age-1 and older spotted bass were more abundant in the upper basin.

  • catch rates of adult largemouth bass and smallmouth bass were highest in riprap and lowest in gravel habitats in both spring and fall samples, and fish were smaller in gravel habitats in both seasons. Spring catch rates of spotted bass varied unpredictably among five habitats, but fall catch rates of this species were highest in rubble habitats and lowest in cove and mixed substrate habitats. Catch rates of largemouth bass and spotted bass were lower in fall than spring; however, catch rates of smallmouth bass were higher in fall than spring. Managers designing electrofishing surveys to obtain a random sample of black bass should be aware that electrofishing catch rates vary according to specific habitat preferences of both size and species of black bass.

  • the dynamics of spotted bass populations in reservoirs are poorly-understood and little studied. A critical period for spotted bass was not observed and we could not determine when year-class strength was fixed. Efforts to understand this species are warranted, because they are an important sport fish species in Tennessee reservoirs. Since 1991, spotted bass have represented as much as 40% of the total black bass catch and 60% of the black bass harvest from Normandy Reservoir.

  • production of larvae by threadfin shad and gizzard shad varied over two orders of magnitude and was inversely related to adult threadfin shad abundance. Winterkills of threadfin shad were size selective, killing all fish under 60 mm TL but allowing some unknown percentage of larger fish to survive. When threadfin shad stocks were reduced by winterkills, surviving threadfin shad and gizzard shad may have taken advantage of less competition for food resources in early spring and increased condition enough to spawn successfully.

We initiated the habitat manipulation phase of the study in 1995. Three types of habitat improvement structures (cypress tree plantings, furring strips, and brush piles) were constructed and use of these structures by littoral fishes, including black basses, was evaluated during the summers of 1995 and 1996. Mean catch of juvenile largemouth bass and spotted bass did not differ between habitat-improvement sites and unmodified sites either year. We found little beneficial effect of habitat enhancement structures in Normandy Reservoir. Habitat enhancement is costly, time-consuming effort, and appears to offer little promise of enhancing year-class strength of black basses in Tennessee reservoirs. To construct a total of fifteen 50-m sections of brushpiles, furring strips, and cedar tree habitats on Normandy Reservoir, we spent approximately $1200, or roughly $80 per 50-m of habitat. Any increase in black bass year-class strength via habitat enhancement would probably be outweighed by the typical increase observed in a high- water year. Trying to duplicate the positive effects of high water using artificial habitat enhancement would involve changing the habitat in virtually the entire reservoir, which would be prohibitively expensive. Attempts to enhance year-class strength of fishes in Tennessee tributary impoundments should focus on altering the hydraulics of systems and not shoreline habitat.