Text Box: Stream Tender Magazine

“ December 2013 Issue”

 

FISH HABITAT  -  A BASIC UNDERSTANDING

Three Basic Components of

Fish Habitat

Water

Riparian Habitat

Structure

Water

Structure

Riparian Habitat

Riparian Habitat

Woody Debris

Rocks

Weeds

Undercut Banks

TROUT SPAWNING HABITAT

    There is one specialized type of trout habitat that is very important to the on going survival of the species, and this is spawning habitat. Without it, reproduction would be impossible!

    Trout require a clean gravel substrate, with adequate depth of water and the right velocity of flow. Also, the gravel size range needs to be just right for each mature female trout.

    Trout need to fan an egg

nest in the gravel with their tail, so it is important that the gravel is the right size, relative to the size of the female trout.

    Once the eggs are laid and fertilized, the female will fan a cover of gravel to protect the eggs and allow water to percolate thru, while the eggs incubate. A good supply of well oxygenated water is a must for the eggs to hatch.

    The stream gravel aggregate size for spawning trout is usually a mix of some

fine pebbles, with gravel ranging in size, with a few larger stones in the mix. The larger stones add stability to the redd or nest, so that high flow events don’t move the materials in the redd.

    Spawning gravel deposits in streams, are usually enhanced by both boulders and large woody debris that collects pockets of gravel in the right size range for spawning trout.

    Also, adequate velocity is

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TROUT FOOD  -  HABITAT

 

 

 

    Trout feed primarily on aquatic invertebrates. These are small insects that have an exoskeleton, instead of a vertebrae, thus the name.

    Invertebrates that reside in trout streams, utilize the same structure as trout for their habitats. Rocks, weeds and woody debris provide an environment where this fish food can thrive.

    Aquatic insects will also

live in the substrate of streams. Varieties of invertebrates have adapted to burrowing into the stream bed or find habitat in gravel, cobble and detritus.

    These insects provide a food source for resident trout and without them in good supply, fish would not be able to survive.

    Most of a trout streams invertebrate population goes thru a life cycle that includes

The transformation into an airbourne insect, where it emerges from the water into the atmosphere.

   Aquatic invertebrates that transform into a flying insect, do so for reproductive and distribution purposes. During this emergence and when the insects return to the water to lay their eggs, trout will feed on them with determination.

    Trout will also feed on terrestrial insects that live in the riparian zone. A few good examples are grasshoppers, ants, beetles and earth worms. These insects will fall or get blown into the water, where trout will eat them up.

 

 

 

 

 

    Aquatic invertebrates require clean and pure water to survive!

Above: Burrowing nymphs such as this Brown drake, will burrow into a streambed of silt, sand and detritus.

Above: In the adult stage of this mayflies life, it will emerge from the water and fly thru the air, before laying its eggs back into the water.

required to create gravel collection, during run-off events. The gravel present in a trout stream is continually replenished by eroding steam banks upstream.

    One of the most common negative impact on our foothill streams is silt loading. If too much silt is present in a trout stream, the gravel spawning habitats can be smothered in silt. This can often happen after the eggs have already been laid down.

Right Photo:

    The photo on the right shows a pair of brook trout trying to fan a clean nest of gravel on the stream bottom. As you can see, there is a considerable amount of silt and sand covering the spawning gravel.

    It is doubtful that any of the eggs would survive thru an incubation period, under such conditions. Soon after the eggs are laid down, a new covering of silt will smother them! This is a common sight on many of our area trout streams!

Right Photo:

    This photo shows a trout redd that was made by brook trout on a clean gravel bottom of a spawning tributary. The redd is distinguished by the very clean gravel patch shown in the photo. The surrounding area is gravel with a covering of algae or rock moss. Soon the trout redd will also start to change color and darken.

    What is fish habitat? To start to understand fish habitat, you first must learn from the basics. Fish require water, habitat and food to survive. The quality of these three requirements determines how well fish do in any given environment.

    There are two environments that freshwater fish inhabit, those are lake and stream habitats. Because this magazine focuses on stream environments, this article will  cover that particular topic.

    Also, because trout is the primary variety of fish that is mentioned in this publication, we will focus of trout habitat.

    Trout stream require three basic components to support populations; riparian habitat, clean and cold water and structure that trout can utilize for both cover and as a feeding habitat.

    Submerged structure habitat consists of three primary things; weeds, rock and woody debris. Emergent cover habitat is provided by

undercut stream banks, over hanging branches, limbs and grasses, etc..

    In-channel, submerged or partially submerged structure will also help to break the velocity of flow in a stream, creating holding habitats for trout. Especially in riffle areas, where the depth and surface disturbance created by the  gradient is sufficient to hide trout from predators.

    Flow dynamics will provide cover for trout by altering the surface of the stream’s water.

 

   

   The surface chop created by a riffle or counter acting currents can blur the visibility of clear water. This will make it difficult for predators to see trout holding near the bottom of a stream. We can consider this habitat as well.

    Once you understand some of these basic components of what fish habitat is, you will have an easier task in furthering your knowledge of the topic.  The task of being able to know complexities of where and why trout use particular habitats, adds a whole new element to how you look at a stream. This is called “reading water”.

RIPARIAN HABITAT

    Riparian habitat is of primary importance to the health of a trout stream. Without a healthy buffer of mature willows, trees and grasses, a stream is susceptible to bank erosion and channel widening.

    For the trout that reside in a stream, the constant input of woody debris from a healthy riparian zone, creates necessary in-stream habitat under the water’s surface and along its banks.

    During high flow events in the stream, willows and trees can be washed into the stream channel, from undermined stream banks.

    The weight of winter snow can bend willow limbs down into the stream channel, or wind can blow down dead or dying trees onto the water’s surface. All of this woody debris will enhance fish and aquatic invertebrate habitat in the stream channel.

    When a healthy riparian buffer exists along the water’s edge, the flow in the stream channel is constricted. This narrow channel width provides the necessary scouring, to keep the streambed clean, exposing boulders, cobble and gravel.

    The trunks of willows, trees and rocks at the water’s edge, work as debris catchers, collecting floating wood that travels down the stream channel during high flows.

Right:

A healthy riparian zone provides good Juvenile trout habitat!