bass predation in Florida (Shireman, Colle, and
1978).
Also, grass
carp may escape in large numbers from some reservoirs, and barriers may have
to be constructed.
Case histories
Detailed case histories of grass carp additions to large impoundments
are not abundant, and most are from southern states because problems are most
severe there and carp have been under study for years.
Additional reports
will become available for midwestern and far western lakes and reservoirs in
the near future.
impoundment near Houston, TX, was filled in
Lake
an
1973 and is used for recreation and potable water supply.
By 1981,
had infested about 44 percent of its area, along with Eurasian watermilfoil
In 1981, triploid grass carp were stocked at a rate of 75 per
and coontail.
-1
vegetated hectare (about 23 kg ha
a rate considered to be "overstocked."
Two years later, nuisance plants had been eliminated.
There was also a
reduction in water clarity due to a phytoplankton bloom in the year
following plant eradication (Martyn et al. 1986; Noble, Bettoli, and
1986).
The treatment was a success with regard to protecting lakeshore prop-
erty values and enhancing recreation.
Impacts on drinking water quality have
not been reported.
Lake Conway, a 729-ha multipool impoundment in Orlando, FL, was stocked
with diploid grass carp at a rate of about 15 fish per vegetated hectare
(about 6 kg per vegetated hectare).
In 2 years,
and Nite
were
. .eliminated in all pools, although
was unaffected. The treatment
is considered to be a success. There was minimal negative impact, although
blue-green algae increased and waterfowl population decreased.
Fishing for
largemouth bass improved dramatically (Miller and King 1984).
There are several useful case histories of grass carp introduction to
small impoundments (e.g., Mitzner 1978) and urban recreational lakes (e.g.,
Van Dyke, Leslie, and Nall 1984; Leslie et al. 1987).
costs
Grass carp may be the least expensive means of achieving long-term
control/eradication of some nuisance aquatic plant species (see Table 14 for
lists of preferred and nonpreferred plants).
In southern waters, in partic-
ular, plant harvesting is often either ineffective or too expensive, leaving
herbicides and biological controls as primary alternatives.
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