turbidity and shoreline erosion, perhaps because
previously
wave action.
Erosion in some carp lakes has been extensive enough to
trees along the shore.
In some cases, there have been increases in
particularly nuisance blue-green algae, and a replacement of phytophilic
invertebrate species with bottom dwellers.
A major concern had been the
potential impacts of the high rate of egestion of organic and inorganic
matter.
There appears to have been no report of a "pulse" of nutrients fol-
lowing carp introduction, in contrast to procedures such as herbicide treat-
ments where very large amounts of plant biomass may be left to decay.
Instead, there appears to be a continuous transformation of plant matter to
fish tissue and to egested
that some nutrients in plant biomass
are lost to a "sink" (fish tissue) and the rest to decomposing organic matter.
There have been concerns about negative impacts to other fish species.
Some'investigators have reported enhanced fishing success following elimi-
while others
nation of vegetation (e.g. Bailey 1978, Miller and King
have found interferences with spawning and growth (e.g., Ware et al. 1975,
Forester and Lawrence 1978).
Further studies in this area are required.
There is some speculation that a slow release of nutrients from
carp fecal material can be a subsidy to the planktonic food web and in this
way contribute to enhanced energy flow to game fish.
Overstocking of grass carp can present other problems in addition to the
direct effects of plant eradication.
For example, waterfowl are dependent
aquatic plants for food.
Lakes and reservoirs on significant
may be
important resting/feeding sites and could be avoided if plants were eradi-
cated.
Further, if significant numbers of carp escape to downstream sloughs
and marshes, further damage to desirable communities could occur.
Once stocked, management of fish density has proven to be very difficult
in Florida waters.*
Carp apparently avoid nets and traps and can escape
electroshockers.
It appears that once a lake or reservoir is stocked, users
of the reservoir are committed to their decision until the fish die (10 years
or so).
In summary,
grass carp are clearly an effective,
long-term agent for the eradication of some nuisance aquatic plants.
Their
use in the management of macrophytes to achieve a desired coverage has prover.
Personal Communication, J.
Florida Department of Natural
Resources, Tallahassee, FL.
137
Previous Page
