Types of fish habitat
From marsh to creek and river to lake, the character of the habitat changes along with its role in a fish’s life cycle. Even intermittent creeks found in the uppermost reaches of a watershed can be habitat for part of the year. A roadside ditch or the low area in a farmer’s field or a forested area might dry up in the hot months of summer, but for short periods each year, water flows over the land and may play a key role in habitat.
Because a watershed collects surface water (from precipitation, snow melt, etc.) and channels it across the landscape into small streams, rivers and lakes, the health of fish and habitat is influenced by more than activities that occur within a waterbody, or along the water’s edge. Threats occurring within the watershed and beyond can impact fish and fish habitat health.
By understanding the wide-ranging needs of fish that are served by creeks, streams, rivers, ponds, and lakes, we can better appreciate what fish are up against when we alter the natural environment.
Lakes offer shoreline spawning areas to fish, along with feeding areas in deeper water. The depth of the lake, the water temperature, the abundance and type of plants within the lake, and the substrate (mud, sand, and rocks) of the lake bed are all factors that determine the types of fish that will live there.
For example, deep lakes are usually cold, because the sun does not heat deeper layers of water, and since the penetration of sunlight in the water is limited, the growth of plants on the bottom is also limited. This type of lake is a perfect habitat for lake trout and lake whitefish, who hang out in deep cold water during summer then migrate to shallow areas in fall to reproduce.
Shallow lakes, however, are ideal for yellow perch and other fish that prefer warmer waters and abundant vegetation.
Other species found in lakes depend on the types of creeks and rivers that feed into or flow out of the lake. For example, white sucker leave a lake in spring to spawn in small gravelly streams with moderate currents, and lake sturgeon migrate from a lake to spawn in rivers with fast flowing waters or rapids. For these two species, and for many others, the quality of a lake extends far beyond its immediate perimeter.
Creeks, streams and rivers
Varying flow patterns of creeks, streams, and rivers, such as the alternation of pools and riffles, provide a wide diversity of fish habitat.
Riffles are shallow areas over which the water flows swiftly and where the substrate is coarse-textured (gravel, cobble, and blocks). When the water temperature rises in the summer, riffles provide more oxygenated water to fish. In the winter, the agitation of water in riffles limits the formation of ice to provide precious refuge for fish.
Pools are zones of quiet water that are usually found downstream of riffles. This type of habitat, where the water is often fresher if the pool is deep, can be used as a resting and feeding area.
The stabilization of a bank with rocks or concrete (riprapping, retaining walls), or the installation of weirs or culverts that are too narrow, can speed up the current in certain places and slow it down in others. When we alter the land bordering creeks, streams, and rivers, we may inadvertently alter the flow of water and, in doing so, destroy habitats that are essential to certain fish species.
Wetlands are biologically productive ecosystems that are midway between aquatic ecosystems and terrestrial ecosystems. They include peat bogs, marshes, swamps, and floodplains.
Wetlands provide various kinds of shelters and abundant food resources to meet the needs of young growing fish. This includes species such as bass, walleye, yellow perch, pike, and brook stickleback. Wetlands also support species such as invertebrates, insects, amphibians, birds, and mammals.
In addition, wetlands contribute to the health of other fish habitat types by acting as sponges to retain and slow down the flow of water runoff into lakes and streams and by filtering sediments and absorbing the nutrients contained in runoff before they reach other aquatic environments.
Since they overlap with the terrestrial environment, wetlands are particularly vulnerable to human activities such as infilling and drainage, etc.
Nearshore habitat is the area of shallow water at the edge of lakes and rivers. Many fish species use this shallow, which supports aquatic vegetation, to lay their eggs, hide from predators, and feed on crayfish, dragonflies, and leeches.
If we modify a nearshore habitat by building a dock or by cleaning out an area for swimming, we may be damaging an entire ecosystem and jeopardizing the fish that use it to fulfil their needs. Detailed planning is required before undertaking work at the water’s edge.
Riparian habitat is the strip of trees, shrubs, and grasses that naturally grow along the shoreline. This habitat acts as a buffer between land and water by stabilizing the shoreline with its network of roots and by filtering surface water runoff to remove impurities. Leaves and branches also break the force of falling rain and slow water runoff from entering aquatic environments by allowing it to be absorbed into the ground. This “green line of defence” prevents surface flooding and bank erosion.
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