Importance of Movement–
Seasonal Movements

Some animal movement within streams and rivers are seasonal in nature and represent adjustments to seasonal changes in habitat conditions or movements linked to the life cycle needs of the species.

Changes in habitat conditions, such as temperature, water depth or flow velocity, may require organisms to move to areas with more favorable conditions. During the summer, for example, many salmonid species move up into cool headwater streams to avoid temperature stress in mainstem waterways. When conditions become too dry, these animals shift to areas with suitable water. Floodplain side channels and sidewall channels that are fed by groundwater also provide thermal refuges for fish and other aquatic organisms.

As organisms move through their various life stages they need access to areas that meet a variety of habitat requirements, requirements that may change as these organisms grow and develop. Sometimes spawning habitat doubles as nursery habitat for juvenile fish or larval amphibians. In other cases the survival needs of eggs (e.g. cool temperatures, specific substrates, or well-oxygenated water) may be quite different from those required by juveniles or larvae (appropriate cover, more persistent hydrology, lower flow velocities, or adequate food supplies). Adult fish may require deeper water and larger cover objects.