For grades 4-8


Do you know?

  • Salmon and trout (salmonids) are important to anglers. Salmonids are also important to biologists because their presence helps indicate the health of the stream in which they live.
  • Salmonids are one of the first organisms to be affected if their watery home starts to change or if their habitat is unsuitable. Biologists refer to sensitive animals such as salmonids as “indicator” species. If they are not doing well, it is an indication that there is something wrong with the system in which they live.
  • Because salmonids are so significant, fish biologists have developed many ways to improve stream habitat to enhance fish survival. In some cases, biologists can produce a fishery where none was previously found.

The ecological requirements of salmonids are:

  • Cool, clear, well-oxygenated water
  • Sections of gravel bottom for spawning
  • Occasional pools for feeding and resting
  • Adequate food (aquatic and terrestrial insects, the latter usually falling from streamside vegetation)
  • Cover for protection from predators

Now it’s your turn…

Learning Activity: Features that Improve Fish Habitat

The figure below shows several ways a stream can be improved to provide salmonid habitat. Each structure has been used to meet the special needs of these sensitive fish.

Next to each feature, describe the contribution it makes towards creating a healthy and comfortable environment for fish.


Riffles and Pools

Think about the last time you were at a stream. Let’s review some of the things you might have observed or remember about good fish habitat.

  1. What is dissolved oxygen? Why is it important to streams and fish?
  2. What are pools? What are riffles? What kind of habitat do they provide for fish? Since salmonids spawn in gravel, and gravel is usually found in riffles, riffles are often called “spawning habitat.” The amount of gravel and riffles in a stream (if of good quality) determine the number of salmonids that can spawn there. The places in a stream that provide a place to eat, a place to rest, and a place to hide are called “rearing habitat. “

Look carefully at the drawings.


Learning Activity: Answer these Questions about Riffles and Pools

Answer the questions based on your own experience and the introductory information in this exercise.

Refer to this diagram as you answer questions 1 & 2. INSERT DIAGRAM

Refer to this diagram as you answer questions 3 – 5. INSERT DIAGRAM

  1. Will the dissolved oxygen concentration be higher at the bottom of the pools or the riffles?
  2. Which would give more shelter or protection to salmonid eggs, pools or riffles? Why?
  3. What happens to aquatic insect larvae as the current enters a pool and slows down?
  4. Where would be the best place for salmonid fry to wait for lunch? Why?
  5. Where would salmonid fry use the most energy catching food? Why?
  6. Chum fry spend only as much time in the stream as it takes to get to the ocean (one day to three weeks). Coho salmon juveniles live for a year in the stream before heading to the ocean. Steelhead and sea-run cutthroat juveniles live up to three years in the stream before heading to the ocean. If a stream has good spawning habitat but not much rearing habitat, will it be more likely to support chum or coho salmon fry? Why?
  7. If a stream has both spawning and rearing habitat, which salmonid species might it support? Why?