Aquatic Plant Management and Fish

While plant management activities improve habitat for fish and wildlife, managers are careful to avoid management activities that lead to unwanted effects such as fish kills. Although aquatic plant management activities are often blamed for fish kills, they are only rarely related.

Although most often caused by weather conditions, fish kills can occur from oxygen depletion after plants are killed by herbicides. The dead plants are attacked by bacteria, causing the plants to decay and allowing bacteria to reproduce rapidly. More bacteria use more oxygen in the water. When oxygen gets too low, fish may suffocate unless they escape to more oxygen-rich waters.

When specific herbicides are used on cloudy days, plant managers take dissolved oxygen readings to be sure there is enough present to support fish while plants decay. Learn more about fish kills here.

Goals of Invasive Plant Management as Related to Fish

The Invasive Plant Management Section of the FWC funds scientific research projects at Florida’s universities to improve the state’s invasive plant management programs. Finding cost-efficient control techniques and insuring these control methods are effective, safe, and environmentally compatible is the goal.

There is a common misperception among anglers that aquatic plant managers kill aquatic plant species in a waterbody without regard to fisheries. When invasive aquatic plants are managed soon after introduction, they can be controlled at a low cost while protecting the integrity of the native plant community. Once established, however, managing invasive aquatic plants is difficult and expensive.

Therefore, the goal and statutory requirement of aquatic plant management is the coordinated and consistent management of invasive plants to maintain the plant population at low levels or maintenance control. This level is determined by experienced FWC biologists and other professionals, and is influenced by factors including funding, available technology, and current environmental conditions.

By law, plants may not be controlled in public waterbodies without first consulting with fisheries biologists from the Florida Fish and Wildlife Conservation Commission (FWC). Coordinating with FWC assures that objectives and methods are compatible with fisheries, waterfowl and other wildlife functions in and around the water body. When plants are under maintenance control, operations can be curtailed for short periods to accommodate natural occurrences like fish spawning or human uses such as fishing tournaments.

Research has been conducted to find the most suitable assemblages of aquatic plants, the most appropriate control methods, and the best times to control invasive plants, all to promote long-term sustainable fisheries. The Invasive Plant Management Section of the FWC funds scientific research projects at Florida's universities to improve the state's invasive plant management programs by finding cost-efficient control techniques and insuring these control methods are effective, safe, and environmentally compatible. Learn more at the FWC Research Program site.

Freshwater Commercial and Sportfishing

Freshwater fishing alone contributes over $2.5 billion annually and nearly 25,000 jobs to the economy. Aquatic plant management is essential to the future of such an important recreational and economic resource.

Commercial fishing is a multi-million-dollar industry in Florida, especially on lakes such as Lake Hancock, Lake Apopka and Lake Deeton. According to a study sponsored by the American Sportfishing Association, freshwater fishing generated more than 2.4 billion dollars in economic activity (including retail sales, tax revenues, salaries and business earnings) in Florida in 2006. Learn more about the economic impact of sportfishing in Florida.

More than $2.4 billion in freshwater fishing revenue is generated by more than anglers in Florida annually. About one-fifth of the 1.4 million freshwater sport anglers are from out of state. They fish for black bass, panfish, crappie, white bass and striped bass, catfish and other fish.

In 2010 the FWC stocked almost 3 million fish in Florida waterbodies.

Lake Enhancement

Muck removal/restoration of Lake Tohopekaliga, FL

Lake Tohopekaliga is a "world-class bass fishing lake" near Kissimmee. It has been the most intensively managed public waterbody for hydrilla in Florida for the past decade. Excessive muck accumulation and invasive plant infestations threatened this premier fishing lake, which is also critical for flood protection, irrigation water for surrounding farms, and endangered species such as whooping cranes, eagles and snail kites.

In 2003-2004 Lake Toho underwent a drawdown and subsequent removal of plants and muck by bulldozers and trucks. The project included the removal of more than 9 million cubic yards of muck from more than 3,700 bottom acres. The lake was then allowed to refill from summer rains. The last truckload of muck was removed and refilling began on June 15, 2004. The natural plant seed bank gave rise to healthy stands of knotgrasses, bulrushes, eelgrass, and other desirable plants. Managers continue to treat the lake for problematic plant species such as hydrilla and hygrophila.

Watching Fish

A largemouth bass and two bluegills can be seen easily in the clear spring water. Aquatic vegetation provides important habitat for these fish as both food and refuge from predators.

Several theme parks and state parks offer tourists and residents the opportunity to observe Florida's underwater fish communities through a window or glass-bottom boat.

Crystal clear spring runs, such as the Ichetucknee River, allow snorkelers and scuba divers to get close to a variety of aquatic inhabitants. Observing fish in their natural habitat is a great way to spend a day along the water. Learn to identify a few of the more popular species that inhabit the state.

Anadromous Fish

Striped mullet are anadromous; they can be found in both saltwater and freshwater environments here. These fish were photographed in Fanning Spring, which feeds into the Suwannee River.

Anadromous fish are those that migrate between saltwater and freshwater They occur in Florida's rivers, springs, and connected lakes and are an essential part of the freshwater ecosystem. These migratory animals collect nutrients from the ocean as they grow and transport them upstream into freshwater habitats.

Each year the U.S. Fish and Wildlife Service stocks numerous anadromous fish into Florida's freshwater ways including:

• Mullet
• Sheepshead
• Tarpon
• Snook
• Sturgeon

Protected Fish

Gulf of Mexico sturgeons live in coastal rivers from Louisiana to Florida during the warmer months, and move to the Gulf of Mexico, estuaries and bays in the cooler months. In Florida, they are commonly seen in the famous Suwannee River. It’s not unusual for anglers, boaters and others to observe this fish jumping high above the water surface. While exciting to witness, boaters have suffered injury or even death from collisions with this fish.

A few rare and protected fish species are found in Florida's waterways. The state's most notable protected fish came close to extinction in the 20th century. The Gulf of Mexico sturgeon is an unusual looking and primitive fish that can exceed 200 pounds in weight. It is not unusual for anglers, boaters and others to observe this fish jumping high above the water surface. While exciting to witness, impacts with boaters and jet-skiers can cause injury and even death.

The protected sturgeon spawns exclusively in the Suwannee, Yellow and Apalachicola Rivers on Florida's Gulf Coast. Researchers believe that less than 2,000 sturgeon remain in Florida. Research is underway to rescue the sturgeon from extinction. For more information about the Gulf of Mexico sturgeon, see this article by the University of Florida, Department of Fisheries and Aquatic Sciences.

Non-native and Invasive Fish

Convict Cichlids

Nearly 50 non-native fish species are invading Florida's fresh waterways including tilapia (Nile perch), Oscars, various cichlids, piranha, Asian swamp eels and others. These troublesome invasives have been introduced to Florida's natural aquatic habitats by aquarium enthusiasts, commercial fishing industries, well-meaning regulatory or government agencies, and as escapees from ornamental ponds and zoos.

Once a non-native fish becomes established in Florida's aquatic ecosystem, it competes with native species for food and habitat and can disrupt the natural balance of Florida’s biodiversity. Once non-native fish have become established, it is difficult to eradicate them.

Unusual cold spells and occasional freezing temperatures can help reduce invasive populations. For example, millions of tropical South American plecos, invasive fish introduced by the aquarium industry and often released by aquarium owners, were eliminated when below-freezing weather hit Lake Kissimmee in 2001-2002.

View more information and pictures of Florida's freshwater exotic fishes at the FWC Non-native Freshwater Fish page.

Grass Carp

Chinese Grass Carp

The use of non-native herbivorous fish, such as the grass carp (Ctenopharyngodon idella Val.), is an important means of biologically controlling aquatic weeds, especially in private ponds and agricultural ditches.

Triploid grass carp that purportedly cannot reproduce are used in Florida under permits from the FWC. Using triploid grass carp makes it less likely that this non-native fish will itself become an invasive species; unwanted reproduction of grass carp could damage the habitats they were intended to restore.

Fish Populations

Fish kill

Declines in fish populations, such as natural "fish kills" and long-term population reductions, can occur for a variety of reasons:

• Stabilized water levels and muck buildup result from the accumulation of organic material on the bottom. This may reduce dissolved oxygen levels and water depth as well as create unsuitable spawning conditions. Most Florida lakes are now connected to one another for flood prevention. People have moved into the watersheds so lakes are no longer allowed to flood and wash organic debris from the lake basin. Businesses and agriculture rely on a stable water supply so few lakes are allowed to dry up and burn as in the past. The result of this stabilization is dense growths of invasive and even native plants and the corresponding muck buildup which hinders fish habitat.
• Invasive plant infestations resulting from a lack of management limit the growth of fish, and limit spawning sites of certain fish such as bass. Invasive plants can cover the water and prevent air/water interface, contributing to lowered dissolved oxygen.
• Low dissolved oxygen occurs when bacteria decompose plants and other organic matter, such as leaves and sediments. This process can suffocate fish and other organisms. Low dissolved oxygen may also occur when invasive plants such as water hyacinths form mats at the surface, sealing off the air/water interface.
• Lack of food for young fish (fry) occurs when too many plants are eradicated from a waterbody, and when microscopic animals that small fish eat are removed.
• Low water levels create competition for space, food, and shelter, and make it easier for anglers and predators to catch them.