Why should we care about a fish’s world? Well, because fish are more than an important source of recreation and commercial revenue. They are key players in the complex aquatic balancing act that keeps our rivers and lakes healthy and our ecosystems strong. Yet most of us do not have the faintest clue where in the water fish actually live, let alone what they require to survive. It is not surprising then, that even with the best intentions, a cottager thinking of rearranging their shoreline or a developer considering a lakeside investment has little idea how to avoid harming fish habitat.
Even on dry land, our actions – spreading chemicals on fields and lawns, letting sewage seep from faulty septic tanks or paving roads and walkways resulting in increased runoff – have consequences for the waterways in which fish live. Wherever land actually meets the water, the physical changes we make too often completely rearrange nature’s design for the underwater world.
So we need information. For anyone who lives, plays, or works around water, the answers are in this and other booklets on conservation and stewardship, including The Dock Primer and The Shore Primer. The Fish Habitat Primer-Prairies Edition is an essential guide to recognizing and respecting the environments on which fish depend to keep their – and our – waterways vibrant with life.
Fish, like humans, require certain characteristics of their environment for their survival. For fish, these essential prerequisites include a dependable food supply, a place to spawn (reproduce), adequate cover and reliable migration routes. Those parts of a fish’s world that contribute to sustaining these life requirements are what we refer to as fish habitat.
You may stop a fish’s life cycle from getting started in the first place by eliminating the places they need to lay their eggs. Most fish are fussy about where they spawn. They may require a rock shoal in a lake, or the vegetation of a spring-flooded stream bank, or the boulders at the base of a waterfall. These prime areas where fish choose to spawn are often so important that other fish species may also choose that same location. If suitable spawning sites are in limited supply, or if they are altered, the overall fish population and diversity may be compromised.
Many fish will travel long distances to find just the right spawning habitat. Walleye will migrate considerable distances up rivers and streams in search of gravels and cobble found in quick flowing water, or will seek out specific locations along windblown shoals or shorelines with gravel and cobble bottoms. Walleye spawning takes place at night in water less than one metre deep, possibly along your small piece of shoreline (even though you may never actually see them!).
Spawning preferences vary quite a bit between fish species. Lake trout prefer wind-swept rock shoals, while northern pike prefer the spring flooded banks of streams or the marshy edge of a lake where the pike’s eggs can stick to the vegetation. Not only can the spawning areas be different for each species, spawning times can vary as well. Spawning times are generally dictated by the temperature of the water. Northern pike spawn early in the spring, heading out into the icy waters in search of their spawning grounds. Catfish spawning follows in the warmer months between May to July. Lake trout and whitefish wait until the fall before they begin their spawning activities, while burbot, a freshwater member of the cod family, lays its eggs under the ice during the winter months.
Once hatched, young fish need to eat – plankton, insects, or other smaller, less fortunate fish. The type and amount of food available for the fish depends on the presence of diverse, healthy shoreline areas that are rich in food and that provide great hiding places for fish to lie in wait. While it may not be obvious that cutting back plants, shrubs and trees from the edge of a stream or lake can affect fish, these areas are actually very important, as they often provide the basic food supply for the bugs and smaller fish at the bottom of the aquatic food chain.
Fish, depending on the species, can be both predator and prey. As prey, fish increase their chances of survival by seeking out hiding places where they evade predators. Great hiding places are often found in the shallows where logs, boulders and aquatic vegetation can be found. When we clear these materials from our shorelines to “tidy up” the swimming area, we have carried out an unwanted house cleaning for the resident fish populations. Other potential hideouts can be found in deep water and in the shadows of an undercut stream bank. The types of hideouts might even vary over the course of their lifetimes. As an example, the young northern pike lurks at the edge of shorelines near vegetated areas and fallen logs to escape bigger fish predators. As the pike grows bigger, it ventures further offshore to deeper water to use aquatic plants and submerged timber as cover so that it can ambush prey of its own.
All species of fish require the freedom to move from one type of habitat to another as seasonal changes and life cycle urges dictate. Most people are already familiar with the idea that many species migrate upstream to spawn and that dams and other obstacles can block fish from accessing these important spawning beds.
Since fish can travel great distances within a watercourse to spawn or feed, any activity that blocks their migration can disrupt whole populations. Walleye, for example, are renowned for their determination to reach their spring spawning grounds. They fight their way upstream and can even negotiate white water rapids. But even this species’ strong swimming skills and persistence can be thwarted by human-made roadblocks such as dams. Other common barriers to migration are undersized culverts that can funnel a lazy creek into a high-velocity jet of water. Fish may be unable to fight their way upstream through this unnaturally fast water. Undersized culverts may stop or delay migrations of strong swimmers, such as walleye and suckers, and can pose an even greater threat to weaker swimmers such as northern pike. These impacts can often be lessened or avoided by installing a wider culvert or bridge to allow fish to migrate easily both up and down stream.
Even seemingly innocent human activities can have a significant effect on fish populations. What’s more, while most fish are able to respond to changes in their environment by simply moving from one area to another, some species are less adaptable and are tied to a particular critical habitat. Critical habitat is generally defined as an area or environment type that a species absolutely requires in order to carry out some or all of its life processes. For a spawning bull trout, an “upwelling area” in a coldwater stream is a must. In this area, groundwater percolating from below the redd (nest) oxygenates the eggs and keeps them from freezing during the over-winter incubation period. Since these upwelling areas are usually few and far between, entire populations of fish may end up “putting all their eggs in one basket”. The loss of these areas can be critical to the health and overall survival of an entire fish population. In cases where a project is proposed to be constructed in an area that has critical fish habitat, the best line of defence is to relocate the project to another area, often not far away, but safely removed from the critical habitat.
If we tinker with the water quality by degrading it with sediment, pesticides, or spilled chemicals, we will force a fish to find a new home, or worse – go belly up.
Most fish species have certain temperature requirements and will seek out waterways that best suit their needs. Some fish are restricted to narrow temperature ranges, while others can adjust easily to a wide range of temperatures. If you take the temperature of a water body, you can probably guess who might live there: coldwater, coolwater and warmwater environments all have a different set of residents. Lake trout require cold, thermally stable water that maintains an average temperature of less than 14°C, even on very hot days. Lake whitefish, walleye and northern pike prefer slightly warmer water while bass, bullheads and suckers thrive in warmwater with average temperature up to 23°C, levels lethal to other species. By cutting down the overhanging vegetation that provides shade, we can turn the water thermostat up or down with sometimes devastating consequences.