An exclosure protecting American pondweed and spadderdock so that they can become established. These two native species of aquatic vegetation provide quality physical habitat, shoreline stability, and improve water quality. Photo courtesy IDNR Division of Fisheries.
The term “habitat” encompasses all aspects of an organism’s environment, both biotic (e.g., plants) and abiotic (e.g., temperature), that are required for it to live and thrive. We most often use the word when describing only a particular aspect or the more obvious physical features of an organism’s overall habitat. For example, grasses and forbs are referred to as habitat for prairie-dwelling species. While these physical features are an important part of a species’ overall habitat, less obvious aspects of habitat and the interactions between them are sometimes overlooked.
The term “aquatic habitat” is used most often when referring to physical objects in a waterbody, whether they be naturally occurring like a fallen tree or artificial structures that are built and placed by Illinois Department of Natural Resources (IDNR) fisheries biologists and angling groups. Other examples of physical habitat include gravel beds or hollow stumps used by fish for spawning, rocky areas for hiding and foraging, or pools and riffles in the case of rivers and streams. These physical habitat features are usually the focus of habitat improvement projects in Illinois impoundments, in part because most impoundments are several decades old and much of their original physical habitat has long since become degraded from decomposition or sedimentation.
Adding new physical habitat to impoundments can provide fish with places to hide from predators, forage for prey and to spawn. Anglers also can benefit from the addition of physical habitat, as the new habitat tends to concentrate fish, making them easier to locate.
Options for physical habitat are limited only by your imagination. A simple internet search will produce an abundance of different designs for fish habitat structures. The best designs to use will often depend on the fish community in the waterbody, the depth where the habitat will be placed, and your propensity towards humanmade vs natural/biodegradable material.
One of my favorite methods is the use of invasive shrubs (bush honeysuckle, autumn olive, etc.) weighed down with cinderblocks, as they provide great physical habitat for both young and adult fish, while simultaneously removing an invasive species from terrestrial habitat. Though habitat improvement projects are often implemented for their benefits to fisheries, many other aquatic species reap the benefits as well.
Another important, yet sometimes maligned, type of physical aquatic habitat is vegetation. Though it can become a nuisance to anglers, boaters and pond owners when overabundant, aquatic vegetation is an integral piece of physical habitat for many species of fish, not to mention many other aquatic organisms.
Aquatic vegetation provides oxygen to the water, shelter from predators for young or small fish and areas of increased macroinvertebrates. The macroinvertebrates subsequently provide fish with prey. In impoundments, undesirable plant species, such as duckweed, watermeal and filamentous algae, can take over and cover the surface of the waterbody when there is inadequate rooted vegetation to utilize the available nutrients. By establishing native species of vegetation, you can simultaneously improve aquatic habitat while discouraging the growth of undesirable species of plants and algae. Aquatic vegetation is also one of the primary means of improving another sometimes-overlooked aspect of aquatic habitat, water quality.
One of the most critical components of habitat for fish is…. water! The physical, chemical and biological properties of water are collectively referred to as water quality. Illinois is fortunate to have fertile soil across much of the state. This fertility, coupled with anthropogenic (human caused) changes to the landscape, can, however, contribute to degraded water quality in some aquatic systems.
Excessive levels of nutrients and sediments due to run-off are common across many aquatic systems in Illinois and can greatly hinder the quality of fisheries in those waterbodies. Thankfully, there are things we can do to reduce the amount of nutrients and sediments entering our waters. Agricultural practices, such as no/reduced-till, terraces and buffer strips, can greatly reduce nutrient/sediment loss from farmland, while delayed fertilizing can reduce the amount of time nutrients are susceptible to loss via runoff.
Maintaining vegetated buffer zones around lakes, streams and ponds can help slow down runoff, allowing nutrients and sediment to settle out before reaching the water. Vegetated shorelines also help prevent erosion from wave action and stream flow, which can cause banks to slough off into the waterbody. Another way to limit the effects of nutrients and sedimentation is to establish aquatic vegetation.
Nutrients and aquatic vegetation are two closely tied aspects of habitat. Aquatic vegetation benefits from a particular range of nutrient levels, similar to a backyard vegetable garden. Garden soil that has low levels of nutrients produces plants that grow poorly, if at all. If you fertilize those plants too heavily, however, they can grow out of control or ultimately shrivel and die. In aquatic systems there similarly needs to be enough nutrients to allow for balanced biological growth of plants and algae but not too high of levels that the nutrients are at toxic levels or negatively affect natural processes. Plants are great at providing oxygen to the water for fish and other aquatic organisms. When excessive plant material dies off and decays however it consumes oxygen often leading to fish kills. For riparian property owners, including private pond owners, even the minor act of not blowing leaves or lawn clippings into the water can have a positive impact on water quality. Decomposing organic matter, such as leaves and grass, consumes oxygen and releases more nutrients that can then fuel growth of filamentous algae, a common problem for pond owners. Maintaining the delicate balance of nutrients and vegetation is often a main driver of the health and productivity of an aquatic ecosystem.
If you’re interested in improving aquatic habitat in your personal pond or even thinking about building a pond, there are resources available on the ifishillinois.org website under Private Pond Management.
For public waterbodies, keep in mind that it is illegal to place habitat structures without approval of the local IDNR fisheries biologist. Ongoing habitat projects are often looking for volunteers. For more information, contact your local IDNR fisheries biologist and they can help guide your efforts, whether it’s to place physical habitat into a lake, start/find a local watershed group or even provide guidance on private pond management issues.
Habitat improvement can sometimes seem like a complex and daunting task, but together we can all do our part to protect and enhance the habitat in our aquatic ecosystems.
Jim Garavaglia is an Illinois Department of Natural Resources District Fisheries Biologist overseeing eight counties in east-central Illinois.
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