Stocking rates
An appropriate stocking rate is critical to successful aquatic plant
Some managers may choose to stock at a rate that
management with grass carp.
This strategy is achievable with grass carp
will produce plant eradication.
but is also associated with water quality changes and is unlikely to be com-
Stocking rates are directly affected by the
patible with sport fishing.
length of the growing season, water temperature, palatability of the plants,
size of fish stocked, present and desired plant coverage, and preapplication
Fewer fish are needed when the feeding season
plant management procedures.
long, the nuisance plants are palatable, the water body is only partially
plant-covered (perhaps due to harvesting or chemical treatment), and the man-
agement plan calls for some vegetation to remain.
Also, serial stocking,
where fish are added at intervals, usually requires fewer fish than batch
stocking and also allows better management of the rate of plant reduction.
Aquatic plant infestations vary in coverage, biomass of plants per unit
area, and species.
Grass carp stocking rates such as "rule-of-thumb" formulas
(e-g., 10 fish per acre of reservoir), which do 'not take these factors into
account, can produce a density of grass carp that is too low
there is a
dense, widespread infestation of a nonpreferred or unpalatable plant (e.g.,
spicatwn) or too high when opposite conditions are found.
In one
In the other case, eradication can
case, plant control may not be achieved.
occur.
Stocking rate guidelines, based upon reservoir-specific variables, have
been developed (Bonar, Thomas, and Pauley 1987; Leslie et al. 1987; Wiley,
and these should be consulted.
The most accurate
Tazik, and Sobaski
stocking rates are developed from a program of data acquisition and the use of
one of the computer models.
Models in use now include (a) the US Army
Waterways Experiment Station model (Miller and Decell
(b) the
Illinois Herbivorous Fish Stocking Simulation System (Wiley and Gorden
and (c) the Colorado model (Swanson and Bergersen 1986).
A model for the
Reservoir
Pacific Northwest is under development (Pauley and Thomas 1987).
managers planning to introduce grass carp are strongly urged to consult a
model appropriate to their area or to examine reports by Leslie et al.
and Wiley, Tazik, and Sobaski (1987).
The effectiveness of grass carp is also related to sources of carp
mortality.
Fish less than 450 mm total length are susceptible to largemouth
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