Important Habitat Factors For Salmonids
The word habitat often refers to the physical place where an organism lives. Another related use of the word habitat is to refer not only to the physical place where an organism lives, but also all of the living and non-living factors that define that place for the organism. For example, we could say that the habitat of a certain individual Brook Trout is the deep waters of a lake. And we can also say that the habitat is all of the things about that lake that are important to the Brook Trout. All of these characteristics can be included in a description of the habitat - the characteristics of the lake's water, the physical nature of the lake, the other plants and all the various kinds of animals that live in the lake with the Brook Trout.
Of course other members of the same Brook Trout species may live in a different habitat, such as a stream, or perhaps in coastal waters. Such species are said to utilize a variety of habitats.
Atlantic Salmon always use a variety of habitats for the different phases of their lives: the spend their youth in freshwater stream habitats, move into ocean habitats as the become mature, and finally return to freshwater stream habitats to spawn.
Most Brook Trout do not utilize both freshwater and saltwater habitats. The adult Brook Trout usually live in freshwater lakes or streams, then migrate upstream to the smaller reaches to spawn. However, in some coastal populations the Brook Trout may spend part of their adult life in salt water before returning to freshwater to spawn.
What are some of the habitat factors important to salmonids such as the Brook Trout and Atlantic Salmon?
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Cold Water: Most salmonids are considered cold water fish. Their body chemistry is adapted to the colder temperatures and they survive poorly if the water gets too warm. In addition to being adapted to the colder temperatures, the salmonids depend on cold water to supply the high amounts of oxygen they require.
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Dissolved Oxygen: The same gaseous oxygen we depend on when we breath is also dissolved in water and is available to aquatic organisms for their respiration. Unlike the air where the amount of oxygen is abundant and constant regardless of the temperature, in water the amount of oxygen that can be dissolved in the water depends on the coolness of the water. If the temperature rises above a certain point the water cannot hold enough oxygen to prevent the salmonids from suffocating.
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Clear Water: Salmonids use their keen eyesight to look for the prey they eat. In silt-laden or turbid waters they cannot see well enough to hunt.
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Food: Salmonids are active fish and need ample food, both to be able to move about and to be able to grow. Younger salmonids tend to feed on insect larvae in the streams where they are growing up. Later in life, as they get larger, they begin to feed on smaller fish.
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Protection from Predators: Salmonids need protection from the larger animals that prey upon them such as bigger fish. Many young salmonids are eaten by larger fish. Overhanging vegetation, submerged logs and vegetation, undercut banks and large stones may all create places where the salmonids can hide.
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Shelter from Current: For salmonids living in streams, the need to swim against a strong current and avoid being swept downsteam can use up a lot of energy. To conserve energy salmonids try to find places in the stream where the water current is slower. Here they can rest. Anything such as a large rock or a submerged log may create an eddy behind it which contains slower water. Another place where the water is slower is in the pools at the bottom of riffles.
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Nesting Sites: When it is time to lay and fertilize their eggs salmonids require clean gravel beds. The eggs are laid in nests in the gravel. Water must be able to circulate through the gravel and around the eggs. The water carries oxygen to the eggs and carries away wastes. Silt or clay or sand can clog up the spaces between the gravel and prevent the water circulation. This may lead to suffocation of the eggs.
These are just some of the factors important to salmonids, but they are some of the most distinctive ones. There are many other factors which must be considered. For example, the pH or level of acidity in the water must be within certain limits. Salmonids are tolerant of a fairly wide range of acidity levels, but sometimes acid rain or the drainage from mines may make the water so acid the salmonids cannot survive.
It is very important to emphasize that ALL of the habitat requirements must be met before the salmonids will be found in a given habitat. If even one factor is missing or outside of the acceptable limits the salmonids will not be able to survive.