Tail water fisheries experience regular, consistent water flow and temperature compared to natural streams, allowing fish longer growing seasons and healthy habitat for invertebrates that the fish eat. At the same time dams prevent fish from migrating to headwater streams to spawn. These dams also trap gravels upstream that otherwise would move through a river during natural flooding and thus replenish in-stream spawning areas with new gravel that often gets silted over or scoured to other locations.
It is known that rainbow trout spawn in some areas of the main stem South Fork Boise, despite the loss of spawning gravel. Typical spawning areas are found along braided sections of the river where smaller side channels carry less water and contain smaller gravel conducive to fish spawning.
Updating information on the spawning areas is needed because the main river lacks the smaller sized gravels commonly found in a natural river. Boise National Forest biologists have conducted spawning surveys the past couple of years and have recorded locations -see a map of the 2007 survey at the link below. Volunteers are welcome to assist and observe this effort which is planned for May12-14. The survey is also planned to be extended downstream of Danskin Bridge to the beginning of the canyon reach.
2007 Spawning Redd Survey – map by USFS Boise National Forest
By understanding the behavior of in-stream spawning activity and its increasing or decreasing trends, inference can be made about future populations as well as areas that should be monitored for affects that would be detrimental to future spawning or that could be improved with a variety of improvements encouraging additional spawning behavior.
