Better Fishing Means
At Bowman-Haley Reservoir
North Dakota Outdoors - June 1995
By Joe Bonneau, Dennis Scarnecchia, and Emil Berard
Although the word origins of the fish called carp and the word carping
(to complain in a peevish manner) are different, as far as sport fishermen
are concerned, carp and carping often go hand in hand.
In North Dakota's midsized reservoirs, overpopulation of undesirable or
"rough" fishes, can reduce numbers and diversity of more popular
fishes and harm sport fishing.
First introduced into the United States as a potentially important food
fish, the carp was stocked throughout much of the country in the 1880s and
1890s. The species spread rapidly, so that by early this century a fish
still highly esteemed throughout much of Europe was considered a pest in
the United States, a reputation that, with few exceptions, it retains to
Carp are primarily bottom (benthic) feeders, eating a variety of animal
and plant life (although it is not uncommon to see carp feeding at the surface
on hot, stagnant summer days). Overabundant carp can severely deplete lake
bottom food sources needed by species such as yellow perch, bluegills, and
Rooting activities of foraging carp stir up sediment and increase water
turbidity. Turbid water makes it difficult for sightfeeding game fish such
as walleye, sauger, and northern pike to see their food, as well as an angler's
bait. Carp impede growth and establishment of submerged aquatic plants by
directly uprooting plants, and hindering growth as turbid water blocks sunlight
needed for photosynthesis.
Elimination of submerged plants can diminish water quality, because submerged
plants reduce windcaused turbidity and help cycle nutrients. Submerged plants
also tie up nutrients, which helps control algae blooms in nutrient rich
waters. Besides aiding water quality, fish food organisms live on or near
aquatic plants. Some fish species, like northern pike and perch, need aquatic
plants for spawning. Underwater plants also provide cover for small fish
to escape from predators.
How Carp Dominate Waters?
In many nutrient-rich reservoirs, carp may at first reproduce successfully,
resulting in one or two strong year classes in succession. Their long lifespan
(up to 15 years or more) and potential to reach a large size (up to 20 pounds
or more) allow fish from strong year classes to grow steadily, rapidly at
first, but more slowly later on as they become large and exceed natural
limits of their food supply.
Eventually the reservoir is full of large, old carp whose reproductive success
is poor, because the reservoir's carrying capacity for carp is reached.
Growth and survival rates of young-of-the-year are low. Although few young
carp are added to the population, the damage was done when the strong year
classes were produced.
The Old Carp Syndrome may persist for years until a die off reduces the
dominant year classes. If the die off is sudden, the entire process can
start over. This cycle explains why biologists have often removed large
numbers of carp from waters, only to see survivors reproduce successfully
and recreate the Old Carp Syndrome 10 years later.
With fewer old carp, food for younger carp may be abundant. They can grow
rapidly, and quickly reach a size too large for predation. This rapid growth
permits a carp to live most of its 15 or more years without risk of predation.
The carp's high fecundity (reproductive capacity) up to 2 million eggs
in a 20-pound female and its adaptability to spawn in different situations
gives it an edge over many native or preferred species.
In addition, poor landuse practices in a watershed can result in excessive
sediment input and nutrient enrichment in a lake, conditions which often
favor rough fish over other species. Good land use practices become especially
important in reservoirs draining large watersheds, a common situation on
the Great Plains.
Because carp can alter their own aquatic habitats to the detriment of other
species, and because they can quickly outgrow predation, fishery managers
must often intervene in carp-dominated waters to reduce their numbers. Contracts
with commercial fishermen for harvesting them have often been used, but
economic returns of harvesting and marketing carp are marginal.
In ponds and small reservoirs (less than 300 acres), a common approach to
restoring a desirable fish community is complete eradication of the fish
community with rotenone. Rotenone, a natural fish toxicant, biochemically
inhibits oxygen use by fish. After the eradications, the waters are typically
stocked with more desirable species.
Midsized reservoirs with carp create special problems because eradication
is usually too expensive. Other methods must be developed to manipulate
a fish community, improve water quality, and rehabilitate the sport fishery.
For this reason, the North Dakota Game and Fish Department has begun a three-year
project on Bowman-Haley Reservoir to evaluate methods for controlling undesirable
species in "problem" midsized reservoirs.
The intent of the project is to develop an effective approach for sustaining
a quality fishery, and incorporate the approach into a long-term management
plan for this and similar-sized reservoirs with carp problems.
Bowman-Haley Reservoir is a 1,750 acre impoundment on the North Fork of
the Grand River located 20 miles south of Bowman.
Despite repeated stockings of game fish, fishing success has gradually declined
as rough fish thrived. In 1993, the fish community in Bowman-Haley was dominated
by an estimated 1.5 million pounds of carp, nearly all of which weighed
at least five pounds and were at least 12 years old.
Submerged aquatic plants were nearly absent throughout the reservoir despite
large areas of shallow water apparently suitable for them. Without aquatic
plants, the reservoir became turbid when wind riled sediments below shallow
water. When the wind remained sufficiently calm for the lake to clear, high
nutrient levels in the clear water quickly gave rise to blooms of bluegreen
Such blooms act much like sediment caused turbidity, preventing light from
penetrating the water and hindering growth of submerged plants. Fishing,
boating, and other recreational uses of the reservoir were suffering. Predators
such as northern pike and walleye have had little effect in reducing the
multitudes of large carp, and disappointed boaters and anglers increasingly
voiced their concerns.
Turning Bowman-Haley Around
As a first step, in summer 1993 trapnets and gillnets were set throughout
the reservoir to capture, mark, and release as many fish as possible. Sufficient
numbers of recaptured, marked fish would allow us to estimate the population
of each species. Fish were marked by clipping a fin.
In early spring 1994 we trapped or gill-netted and removed as many other
rough fish besides carp (carpsuckers, white suckers, and redhorses) as possible,
on the assumption that their numbers were high. In all, more than 15,000
(nearly 73,000 pounds) of these fish were removed. Although we initially
thought that numbers of one or more of these other species were as abundant
as carp, we found they were not sufficiently numerous to present problems.
To remove large numbers of carp with minimal cost and effort, we took advantage
of the carp's tendency to congregate each spring in large numbers in relatively
warm tributaries prior to and during spawning. Bowman-Haley has three such
inflowing tributaries Spring Creek, Alkali Creek, and the North Fork of
the Grand River -- and all were full of carp in the spring of 1994.
During peak carp spawning activity, we positioned long seine nets completely
across the mouths of the three tributaries to prevent carp from escaping
back into the reservoir. The tributaries were then treated with rotenone.
More than 700,000 pounds of adult carp were killed, nearly half the estimated
1.5 million pounds of adult carp in the reservoir.
Carp so dominated the tributary habitats that all game fish combined constituted
less than one percent of the total fish killed by number and by weight.
In essence, the effect of rotenone use on other species was minimal.
After the tributaries were cleared of carp, we placed fences across two
of them to prevent carp from reentering, and monitored bottom food organisms,
zooplankton, water clarity, and submerged aquatic plant abundance above
and below the fences. A comparison of the two locations would help us identify
the effects of carp. Water samples collected before and after the rotenone
applications are being analyzed by the North Dakota State Department of
Health to assess effects on water quality. Of special interest is how decaying
carp affected nutrient levels of the tributaries.
Within 24 hours after the carp were removed, water clarity within the tributaries
increased remarkably; from only a few inches with carp to more than two
feet without carp. The increased visibility above the fences persisted the
rest of the summer.
The clearer water above the fences enabled submerged aquatic plants to flourish,
so that by the end of July, areas less than two feet deep were completely
covered with submerged vegetation. Submerged vegetation abundance also increased
in deeper areas of the tributaries, as well as in the main reservoir. In
areas where submerged plants grew, seine catches of young-of-the-year game
fish were five times higher than in areas without vegetation.
Above the fences, abundance and size of fish food items such as midge larvae
also increased significantly. Along with clearer water, this should allow
for increased growth rates of game fish.
Walleye fry were stocked above the fences in 1994 in anticipation that their
growth and survival might be higher above the fences than below. In 1995,
both walleye and northern pike will be stocked above the fences as well
as in the main reservoir. Growth of these groups of fish will be compared
to determine if there is indeed an advantage in stocking fish in the carpfree
sections of the tributaries.
Once carp numbers have been reduced, a second objective of the Bowman-Haley
project is to evaluate methods of keeping carp numbers low. If carp cannot
be reliably controlled, benefits of initial eradications will not last.
Eradication of carp from the tributaries in spring appears to be a cost-effective
method. In 1994, nearly 50 percent of the carp in the reservoir were removed
by treating less than 180 acres with rotenone at a cost of about $ 11,000.
This spring we will again eradicate carp from the tributaries. Once carp
numbers are low, eradications may only be needed every few years.
We will also evaluate the use of temporary weirs and traps to remove carp
as they migrate upstream to spawn. This trap-and-haul method will permit
the removal of live carp for disposal or potential shipment to markets.
It is likely that improved stream habitat quality in carp-free areas above
the weirs will benefit other fish species.
Rotenone baiting, a technique recently developed, is also being tested as
a means of controlling carp. First, nontoxic food is dispensed from an automatic
fish feeder three times a day for several days until carp congregate there
at feeding time. Food with rotenone is then dispensed. We are experimenting
with feeders in an attempt to attract large numbers of carp necessary for
the method to be costeffective in reservoirs the size of Bowman-Haley. The
best chance for success may lie in baiting carp in the tributaries in spring.
Nontoxic food is dispensed three times a day from automatic feeders.
After several days when carp have concentrated in the area of the feeder,
food containing rotenone is dispensed.
Another method of carp control, used in Bowman-Haley in 1994, is a spring
drawdown of the reservoir. After female carp expel their eggs and fertilization
occurs, the eggs either attach themselves to submerged grasses, weeds, and
roots, or drift into shallow areas.
In 1994, a onefoot drawdown of Bowman-Haley during spawning left many shoreline
areas covered with mats of dried-out carp eggs. The slight ( 1-2 feet) lowering
of water levels for much of the year has an added benefit of reducing erosion
of shorelines by Cleaves, thereby increasing water clarity. In addition
to drawing down the water, North Dakota Game and Fish and the Corps of Engineers
are also cooperating to install wave breaker structures near Spring and
Alkali creeks to reduce wave action, bank erosion, and sedimentation.
Biologists would like to see several changes in BowmanHaley Reservoir as
numbers of carp are reduced. The establishment of submerged aquatic plants
is essential in providing habitat for young game fish, reducing windcaused
turbidity, and decreasing the severity of algae blooms. Because carp and
other undesirable species are sure to reproduce more successfully following
reductions in carp numbers, stocking of predator species is essential to
control numbers of young carp. If predator populations can be increased
and maintained, biologists may not need to intervene as often to preserve
a desirable fish community.
For BowmanHaley and North Dakota's other midsized reservoirs, sound management
practices in the watersheds and a program of controlling and more effectively
utilizing rough fishes, especially carp, are the keys to less carping and
Joe Bonneau is a graduate research assistant at the University of Idaho
and is conducting his doctoral research on Bowman-Haley Reservoir. Dennis
Scarnecchia is Associate Professor of Fisheries at the University of Idaho.
Emil Berard is the western district fisheries supervisor for the North
Dakota Game and Fish Department in Dickinson.
Return ND Outdoors Magazine.
Last modified April 18, 1996