Fish will feel the stress caused by low flows, higher water temperatures and competition for space and food. Low water conditions in spring and fall can cause spawning failures and increased predation on young fish. Also, fish will "group up" to take advantage of pools where the water is deeper and cooler -- making them more vulnerable to anglers and predators. If conditions worsen, fish are lost to stress from the higher water temperature, lower oxygen levels, and reduced resistance to disease. These threats can impact adult trout numbers in future years.
To help preserve a threatened fishery anglers can:
Anglers who practice catch-and-release fishing can minimize the stress they place on fish:
On streams experiencing extreme drought conditions and high water temperatures anglers may want to avoid catch and release fishing as it is difficult for trout to recover under these conditions.
Thousands of trout that have migrated from low-water streams into irrigation ditches can be saved if water diversions are gradually reduced at the end of each irrigation period, according to Montana Fish, Wildlife & Parks fisheries staff.
Irrigators can save trout with a three-day water-reduction plan. Three days before irrigators plan to close off their diversions, they should cut the water flow in half. Then, within the next 24 to 48 hours, cut the flow in half again. The following day the diversion can be completely shutdown.
The gradual water reduction triggers an upstream movement that causes trout to move out of the ditch and back to the main stream or river channel. Concern for the state's fish populations is heightened by the continuing drought conditions.
FWP manages rivers for wild, naturally reproducing trout, so it is important to maintain enough fish in a stream that they are able to naturally reproduce and preserve the genetic integrity of that fish population when conditions improve.
For more information—or to obtain the brochure "Methods to Reduce Trout Losses in Irrigation Diversions"—irrigators can contact their nearest FWP office or local conservation district office.