Web Restoration
Devils Lake was faced with reduced water quality and rampant weed growth, so a plan to restore the lake was written in 1986. The restoration plan for Devils Lake includes:
• Biological control of vegetation with Grass Carp
• Selective area dredging to improve lake flushing
• Control of nutrient sources including septic drainfields, fertilizers, detergents and animal wastes
• Watershed management to limit sediment input
• Public education and involvement
• Interagency coordination
Devils Lake at Horseshoe Bay before Grass Carp.
Grass Carp
Grass Carp, also known as Chinese White Amur.
Common Names:
Chinese Grass Carp or White Amur
Scientific Name: Ctenopharyngodon idella
APPEARANCE: Dark brown to dark gray on top, lighter to cream color below with slight gold-silver sheen on side. Oblong body with moderate to large scales, rounded belly and broad head. Diamond pattern on side.
NATIVE HABITAT: Natural range is eastern China and Soviet Union. They prefer warm water densely vegetated inshore areas 3 - 9 feet in depth and fast flowing, turbid rivers.
AGE AND SIZE: Standard lengths are 23 to 26 inches in females and 20 to 24 inches in males. Grass Carp have been known to grow much larger under ideal conditions. They may live over 20 years but in their native habitat the average age ranges from 5 to 11 years. Those stocked in Devils Lake are a sterile hybrid and are unable to reproduce.
STOCKING: Grass Carp were initially stocked in Devils Lake at a density of approximately 40 fish per acre. Grass Carp have been stocked three times in Devils Lake as follows:
1) 10,000 in September of 1986
2) 17,090 in March of 1987
3) 5,000 in July of 1993
32,090 TOTAL
DIET: Grass Carp are vegetarian and prefer warm water for feeding. When young, Grass Carp can eat their own body weight in weeds every day.
A Devils Lake Water Improvement District newsletter from 1990 states, "Isham, who was hired more for his political skills than his knowledge of lake restoration, puts the official opposition (to grass carp), down to the fact grass carp were at that time associated with the complete eradication of aquatic weeds, which is equally bad environmentally."
"With official approval, backed up by a $250,000 grant from the federal Environmental Protection Agency, 10,000 half-pound carp were purchased from an Arkansas supplier. The other half of the money for the program was provided by local property taxes."
The Manager's Report stated that, "The weed-eating fish were first introduced in September 1986. After three years of intensive study by the Washington Cooperative Fishery Research Unit, University of Washington, it has been established that the $500,000 program has resulted in effective non-damaging aquatic weed control at a cost savings to the district. Grass carp are commonly used for weed eradication in some parts of the world. The Devils Lake Water Improvement District has demonstrated that this technology can also be used for weed control."After the 1993 grass carp stocking, DLWID has taken a closer look at the affects of grass carp on lake vegetation. The grass carp have voraciously eaten all the lakes bottom vegetation. One wonders what the grass carp are actually eating. DLWID will be having special meetings to develop a management plan for the grass carp.
Today there is minimal plant growth in the lake which causes additional problems for fish cover and various environmental concerns. The goal is to use grass carp to keep a healthy balance of plant growth, not eradication.
The grass carp are sterile and there are no plans for additional stocking. This means future control of aquatic plant growth will need to be by another means to prevent the reoccurrence of the 1980's problem.
Devils Lake at Horseshoe Bay after Grass Carp.
Invasive Aquatic Plants
Devils Lake has a long history of aquatic plant problems. Macrophytes (large vascular aquatic plants) obtain their nutrients from bottom sediments.
Aquatic plants will always be a management issue for Devils Lake due to the fact that the lake is very shallow and has an abundance of rich nutrients in the bottom sediments.Devils Lake has also been plagued over the years with several invasive or non-native plant species. Invasive non-native weeds are plants that have been introduced to this region through human activities, and due to aggressive growth patterns and lack of natural enemies in this region, spread rapidly into native plant habitats. This can reduce habitat diversity, food, and shelter for many fish and wildlife species, and the ability of the natural environment to perform a wide variety of important ecological functions
Two of the most aggressive non-native aquatic plant species that have been present in Devils Lake include: Eurasian watermilfoil (Myriophyllum spicatum) and Brazilian elodea (Egeria densa). Eurasian watermilfoil reproduces vegetatively. Its invasiveness stems from its ability to regrow from tiny fragments. This exotic species has been known to grow up to 20 feet in length! In the years following the introduction of grass carp there was a drastic change in plant community composition in Devils Lake. Brazilian elodea invaded the lake and completely displaced Eurasian watermilfoil.
Purple loosestrife
THE INVASION OF PURPLE LOOSESTRIFE
Behind the brilliant guise of purple loosestrife hides an ugly strategy: the takeover of wetlands. Loosestrife is displacing the native wetland plants at an alarming rate. When the conditions are right, a small isolated group of loosestrife plants can spread and cover a marsh in only one growing season. Once established, loosestrife is difficult to control.
The shallow woody root system forms a dense mat, making adult plants difficult to pull. If the entire root is not taken, then it will resprout. If plants are mowed, the stem pieces will actually send out new roots, eventually become anchored and begin new colonies.
Besides these vegetative maneuvers, each plant's flower spike has the capability to produce 120,000 seeds in a single season. These seeds remain viable when submerged for many years while waiting for the opportunity to sprout. Then during a dry summer, these seeds germinate suddenly. Often the dispersal is such that the seedlings have the capacity to completely replace native vegetation.
HOW TO CONTROL SMALLER POPULATIONS
Because purple loosestrife is so widely distributed in the United States, it is unlikely that elimination is possible. But, because the species has not become well established in many areas, halting the spread of loosestrife and eliminating it from newly-invaded areas is certainly feasible.
The key to stopping the spread of loosestrife lies in recognizing the plant when it first appears and eradicating it before it becomes a dominant part of the wetland ecosystem. By implementing the following measures, we can stem the invasion of loosestrife.
By Hand - Generally effective on small clusters up to 100 plants.
• Younger plants can be hand pulled.
• Older plants, especially those in bogs and deep organic soils, can be dug out.
• Roots must not be broken off or they will resprout.
• All plant parts must be removed, dried, and if possible, burned. Plant parts can reroot otherwise.
By Herbicide - May be necessary for clusters in excess of 100 plants (up to 3 acres).
DESCRIPTION OF PURPLE LOOSESTRIFE
(Lythrum salicaria)
WHEN TO LOOK FOR IT: Mid-July through the end of August when it is in bloom and easily recognized.
WHERE TO LOOK FOR IT: It is present on wet soils to shallow standing water; wet meadows, pasture wetlands, cattail marshes, stream and river banks, lake shores and ditches.
WHAT IT LOOKS LIKE:
Growth Habit: Upright hardy perennial, bushy, up to 7 feet tall.
Flowers: Purple-magenta color. Flowers numerous on a long spike; 5-6 petals per flower.
Leaves: Vary, although usually opposite; linear shape and smooth edges. Attached directly (no stalk) to a four-sided stem.
Roots: Woody taproot with fibrous root system that forms a dense mat.
HOW IT SPREADS: It is a prolific seed producer; also grows from underground root and sprouts from broken-off plant parts.
BEAUTY IS ONLY SKIN DEEP! The attractive plumage of purple loosestrife conceals its menacing nature.
WHAT IS PURPLE LOOSESTRIFE? Purple loosestrife is an aquatic plant that is gaining a foothold. You may have seen the plant's magenta flowers which are strikingly evident throughout July and August. This hardy perennial has been introduced from Europe. Because of its exotic origin, loosestrife has left behind all of its natural enemies and multiplies with no checks or balances in North America.
WHAT IS THE MAJOR IMPACT? The plant aggressively crowds out the vegetation required by wildlife, while having no value for wildlife itself. For example, songbirds do not make use of the small hard seed. Muskrat require cattail to build their homes and they show a preference for cattail over loosestrife for food. Waterfowl, especially ducks, shun wetlands that have become dominated by loosestrife. In addition, overall waterfowl production is decreased as habitat is eliminated. Finally, the plant's growth is generally too compact to offer cover, and cover may be as crucial to wildlife as food.a