Triploid grass carp evolve as an aquatic-plant management tool
Fish Busters' Bulletin
Saturday, October 01, 2011
Media contact: Bob Wattendorf
Florida's outstanding freshwater fisheries and many species of
wildlife are dependent on natural aquatic vegetation. Rooted
aquatic plants stabilize shorelines, prevent erosion, reduce
turbidity (muddy water), provide cover for fish to hide from
predators, serve as food for insects and waterfowl, help reduce
algal blooms, provide shade and cover for fish, and serve as a
visible feature to help anglers locate sport fish.
Invasive plant species, however, can be harmful and have few
natural checks. The spread of water lettuce, hyacinth and hydrilla
are prime examples of nonnative plants that require management.
Proposals in the late 1960s and early 1970s to stock open water
bodies with diploid (fertile) grass carp (Ctenopharygodon
idella) to feed on nonnative plants quickly became
controversial. These Asian carp spawn in similar habitats to
striped bass, and naturally reproducing populations could have
gotten out of control and wreaked havoc on native plant and
wildlife communities.
Florida helped lead the way with grass carp research,
determining their food habits and helping create triploid
(functionally sterile) grass carp. Florida biologists also
developed the certification program using Coulter Counters, which
the U.S. Fish and Wildlife Service and many state agencies use to
ensure only triploid grass carp are stocked. However, even with
sterile fish, if too many grass carp are stocked and plants are
eliminated, the problem may last as long as the fish are alive or
longer - and that can be more than 15 years.
Thus far, in Florida, thanks in part to the diligence of
management agencies, there are no documented cases of grass carp
spawning in the wild. Recently, however, Fish and Wildlife
Conservation Commission (FWC) biologists discovered a few diploid
escapees in the Suwannee River, having come from flooding in
bordering states. This caused renewed concern and the need to
repeat the message about the importance of stocking only triploid
grass carp.
So legitimate concerns revolve around use of grass carp and a
full gamut of options for aquatic plant management are considered,
depending on circumstances.In 2008, the FWC participated in "A Risk
Analysis Pertaining to Use of Triploid Grass Carp for Biological
Control of Aquatic Plants." The review concluded that in public
waters, agencies should develop management plans for each stocking.
The safest approach was determined to be an initial herbicide
treatment followed by low-level stocking of triploid grass
carp.
The FWC's Invasive Plant Management Section also recently
concluded a public review process to create a new "Agency
Position on Hydrilla Management" (MyFWC.com/Nonnatives; search
"Hydrilla Position"). The position recognizes that native aquatic
plant communities provide ecological functions to support diverse
fish and wildlife populations. Hydrilla, as an invasive, nonnative
plant, requires management. However, in water bodies where hydrilla
is established, the FWC will manage it in light of the primary use
of the water body. Plans will incorporate public input, be adaptive
and reflect local conditions.
Chemical control is expensive (up to $750 per acre per year).
Mechanical control is even more so - about twice as costly as
chemical control. Biological controls using insects or diseases
have not proved suitable for managing hydrilla, leaving triploid
grass carp as the most effective biocontrol.
These fish can control certain aquatic plants in moderate-sized
lakes at a cost of $20 to $250 per acre. In private ponds, golf
course ponds, irrigation ditches and similar locations, where sport
fishing is not the primary activity, certified triploid grass carp
provide an environmentally sound, cost-effective way of controlling
aquatic plants. Such stockings require a permit from the FWC. The
Invasive Plant Management Section issues nearly 1,500 such permits
annually, saving users money and reducing herbicide use
(MyFWC.com/License; select Aquatic Plants).
FWC personnel also plan and stock triploid grass carp in public
waters. Currently, staff is monitoring about 100 locations.
However, in situations where sport fisheries and waterfowl hunting
are important, the fish may eat too many plants, destroy important
habitat, adversely affect recreation and negatively affect the
local economy.
In summary, FWC uses a permit program to allow citizens to
purchase and stock triploid grass carp as a cost-effective means of
controlling plants in self-contained private waters. The FWC also
saves state money by using fish prudently in public water bodies to
reduce the need for expensive chemicals, but it draws the line at
stocking triploid grass carp in large, open systems where triploid
grass carp are unpredictable and could negatively affect the
state's immensely valuable sport fisheries and the delicate balance
of our natural ecosystems.
- Dave Eggeman contributed to this column. He is
a biologist with the FWC's Invasive Aquatic Plants
Section.
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