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.
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