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The pre-planned and
controlled process of lowering the water level within an impoundment is
termed a
`draw-down'. In nearly all cases, the final stage of this action is
returning the body of water to its normal
elevation.
Originally, projects of this
type were carried out to allow certain work to be accomplished, such as
the
repair of an associated dam or dike system. And, in the first few years
following the completion of the job,
a soon-to-be-predictable change gradually began to be recognized. During
the third year following draw-down
cycle completion, fishing success in the lake began to improve. By the
fourth year, catch rates reached the
point of being termed `miraculous'. While the `cause' was not
immediately known, the `effect' was certainly
being noticed by the angling public. Consequently, the governmental game
and fish activities, anxious to
take any credit which might be due them, began to investigate this
strange phenomenon of apparent fishery
rejuvenation.
The first thing noted was
that the lake in the post- draw-down state was exhibiting the exact same
traits it
had during the first few years after its initial formation and filling.
Biologists had noted the extremely high
productivity of a new fishery during the third through seventh year.
They attributed it to the tremendous
abundance of the lower end of the food chain from the heretofore dry
land and vegetation areas and its
support of the emerging mid-and upper-echelons of the chain, which
eventually sustained the game fish
populations. What appeared to be happening was an `instant replay' of
the highly-fertile early years of the
lake's life cycle.
Early studies showed that
the lowering of a lake's level for a significant period of time allowed
three very
beneficial things to occur. First, it bared the usually thick,
non-contributory vegetation in the extreme
shallows and caused it to die off. Second, the heavy muck accumulations
from numerous generations of
aquatic plants gone by were allowed to dry and gradually dissipate to
some degree. And, thirdly, new plant
and insect life began to take root in the now-exposed, dry shallows
zones.
Given that Man did not
interfere in the process, this latter event was the more influential
factor, in that it
provided a rejuvenation of the lower food chain elements. The first and
second events provided improved
access to the shallow spawning areas required by most game fish species,
and insured a better oxygen
content in the area.
A major finding by fishery
biologists was that extremely dense vegetation in the shallow zones can
actually
preclude the production of oxygen through the normal photosynthesis
process. Oxygen level measurements
reflect that the surface layer of aquatic growth is often relatively
lifeless, but its sheer density can effectively
prevent the penetration of photosynthesis-dependent sunlight to the
plants beneath. No oxygen content
simply means no fish will use the area.
As scientists began to
better understand what was taking place after a draw-down, they noted
that Man
could effectively influence the quality of the outcome. First, game and
fish authorities could plan for
draw-downs when the fertility of a given lake appeared, or could be
expected, to be on a significant decline.
And, they could hold the lower water levels as long as felt advantageous
for optimum results. Second, they
could assist Nature's workload by employing machinery to remove selected
vegetation and bottom muck.
And, thirdly, officials found that they could plant new vegetation which
would actually contribute increased
support of the emerging food chain and new fishery spawns.
Draw-downs have taken place
all over the country. Two of the more recent draw-downs in Florida took
place on the Panhandle's Lake Talquin and the Central Peninsula's West
Lake Tohopekaliga (generally
referred to as West Toho). In both cases, the effect on the fishery was
extremely positive, to the point that
certain slot sizes and minimum- length restrictions had to be placed in
effect to protect the newly-emerging
bass populations.
Talquin's program was
initiated to allow work on the lower dam. Seizing upon the opportunity,
the Florida
Game and Fresh Water Fish Commission (FG&FWFC) made it a cooperative
venture with the Department
of Natural Resources (DNR), the appropriate Water Management District,
and the Corp of Engineers.
A beneficial time-line was
developed, as well as a unique staggered schedule for refilling to the
normal pool
levels. A large amount of grass and other selected vegetation was
planted in key locations and for pre-
determined depths. The staggered refilling schedule allowed the
vegetation to mature to varying degrees
before final inundation and provided a basis for study and analysis.
The eventual result was a
massive increase in the `young-of-the-year' spawn of largemouth bass the
first
Spring after refilling. The second year spawn results was generally a
repeat of the first, while the first year
crop exhibited a very high survival rate and rapid growth. As the
initial post-draw-down spawn approached its
third birthday, the numbers of one and two-pound bass in Talquin began
to amaze and delight the local
anglers. Sadly, many took advantage of the situation to exhibit their
angling prowess to their friends down at
the gas station and failed to practice catch- and-release. The FG&FWFC
found it necessary to impose slot-
size restrictions which, if sustained indefinitely, will greatly assist
in maintaining this fine fishery for years to
come.
West Toho has experienced
deliberate draw-down three times in the past two decades. The first two
were
in 1971 and 1979. The last one, in 1987, was required due to the rampant
vegetation growth in the shallow
zones and the loss of major spawning areas due to decaying muck from
that vegetation. The explosive
growth was caused by the continuous dumping of massive amounts of
poorly-treated sewage from Shingle
Creek on the northwest corner of the lake.
The 1971 draw-down project produced the
following results:
- By the second year, the spawn-produced bass fry density
was up an astounding 450%!!
- In the third year, the population of harvestable bass
(i.e., 12-inches, or larger) had increased 130%.
The draw-down of 1979
produced similar results regarding the densities of new fry produced and
surviving.
The big news, however, was that the harvestable population increased by
an amazing 400%. Now we know
why West Toho continues to produce such great angling experiences year
after year.
During the most recent
draw-down, Nature was provided a major helping hand, thanks to a massive
pre-planning effort, excellent cooperation among the governmental
agencies involved, and an allocation of
operating funds.
The West Toho draw-down was
timed to coincide with a law that greatly reduced the sewage problem
from
Shingle Creek. And, an armada of earth-moving equipment and transport
vehicles were staged to remove
muck and undesirable vegetation to preplanned agriculture areas, where
they would be used as fertilizers.
This cleansing of selected shallows of the lake was very carefully
planned to provided maximum support of
forthcoming fish spawns.
Large plots of new
vegetation were planted on the 60% of the lake bottom which was exposed.
These
provided the start- up of the lower food-chain elements and eventual
cover and feeding areas for the newly
hatched fry of the spawn.
After refilling and the
initial spawn, FG&FWFC biologists reported an explosion of bass fry
in the shallow
grasses, with apparent high survival rates. The second year after the
refilling West Toho, we anglers noted
extremely high numbers of 6-10 inch bass throughout the lake. Today, the
West Toho fishery has an
amazing population of 2-3 pound largemouths. Although the official
figures have not been released, we would
expect the results in spawn success and harvestable populations to rival
the other draw-downs. We are still
awaiting data on the latest Florida draw-down, that being big Lake
Kissimmee. It appears the results will be
impressive!!
So, you see, Virginia,
there really is a Santa Claus and there really is a Fountain of Youth.
They are just like anything else worth having-- we have to believe in
them and work at it a bit..
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