Brook Trout Habitat

The three main factors influencing most trout population are fishing pressure, habitat suitability, and the ability of trout to grow into mature, spawing individuals (MN DNR).  According to the DNR, the trout streams of SE Minnesota are superior to those of northern Minnesota because they are typically spring-fed and have large aquatic insect populations for trout to consume.  Trout, and especially brook trout, are very peculiar about their habitat, having certain physical habitat requirements that must be met.  Below are some of these requirements and pictures of Spring Brook that show these requirements being met.

Examples of why Spring Brook provides such great Brook Trout habitat:

(1) Pool Formation
This photo shows a deep pool formed by a bend in the stream.  These deep pools are an essential part of the habitat required by all stream trout.  Healthy trout streams like Spring Brook have a series of shallow riffles followed by deep pools.  These pools provide trout with a place to swim and hide from predators.  In order for a trout stream to retain the riffle and pool structure, the flow of the stream must remain relatively stable.  Extreme high flow events can cause channel scouring and reduce side pool formation (Hunter, 1990). Occasional high flow events have occured on Spring Brook that have inflicted lasting alterations of the stream channel.

Photo: Deep pool near Decker Avenue Bridge (photo: Jeff Jasperson)

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(2) Clear, Cool Spring Fed Stream

This photo shows a close up of the clear and cool (around 48 F) water of Spring Brook.  Trout, and especially brook trout, require water that is cool and highly oxygenated.  Water at or above 70 F jeopardizes trout survival.  Riffles like the one on the left are well oxygenated because the surface of the water is broken and oxygen from the atmoshphere is more efficiently absorbed. 

Brookies are less tolerant of cloudy water than are rainbow and brown trout (Schmitt, 1998).  Clear water allows sunlight to penetrate to the streambed, promoting plant growth which ultimately provides food for trout.  Clear water also makes it easier for brookies avoid predators, including fisherman.

Photo: Clear, cool water in a Spring Brook riffle (photo:Jeff Jasperson)

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(3) Bank Cover

Prevalent bank cover is a necessary element of every trout stream.  Trout use this cover to escape predators (birds, fisherman, etc.) and to find cooler water temperatures in the areas shaded from the sun.  WIthout bank cover, stream trout do not survive in high numbers.

The removal of bank cover is a frequent problem for streams in urban or residential settings.  If cover is removed and more of the stream is exposed to the sun, the water temperature will become warmer and less suitable for brook trout (Barton and Taylor, 1985).  It is important that wooded corridors are preserved to prevent temperature increases from taking place.


photo: Bank cover along Spring Brook provides shade and places to escape predators (photo: Jeff Jasperson)

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(4) Gradual stream gradient

The gradient of Spring Brook is within the range of highest trout productivity.  The most productive trout streams have a relatively low gradient, from 0.5 to 2 percent, which converts to a drop of 25 to 100 feet per mile (Hunter, 1990).  Streams that have a gradient greater than specified above have swift moving current and must have slack-water created by stream  impediments it it is to support trout.  If the gradient falls below 0.5 percent, a stream is likely to have a silty bottom and water temperatures that are too warm for trout.
           
photo: Spring Brook's gradual stream gradient (Jeff Jasperson)