BILLINGS — Hatching brown trout in the Montana stretch of the Bighorn River got a two-week reprieve Tuesday when federal water managers agreed to stabilize flows from Yellowtail Dam.
As the result of a conference call Tuesday between Montana Fish, Wildlife and Parks, the federal Bureau of Reclamation and recreation interest from Montana and Wyoming, the federal dam managers agreed to continue releases from Yellowtail Dam into the Bighorn River at 1,900 cubic feet per second (cfs).
Late last week, federal officials became concerned that water was not flowing into the top end of Bighorn Reservoir, which is backed up by Yellowtail Dam, at anticipated rates. As a result, they cut back the flow from 1,900 cfs to 1,650 cfs Monday morning. Following conversations with FWP Monday afternoon, they returned flows to the higher level and scheduled a conference call for Tuesday morning.
Spring runoff from mountain snowpacks is later than planned this year because of cool weather. However, those snowpacks are above historic averages and FWP officials believe they eventually will work their way into the reservoir.
FWP biologists believe that brown trout eggs, which were spawned in November and December, now are hatching in shallow gravel beds in the Bighorn River. The young fish will not emerge from the gravel until May or June, biologists believe. If water levels in the river drop, an entire year’s worth of fry will perish within hours. Brown trout populations in the Bighorn River already are in jeopardy because drought forced water managers to drop water levels during critical spawning and rearing months in previous years.
Low water levels at this time of year also could hamper the growth of insects, which feed all trout species in the river.
The federal water managers, meanwhile, must balance agricultural and recreation interest both in the river below Yellowtail Dam and in the reservoir. One goal is to fill the lake to an elevation of 3,920 feet by Memorial Day. That is about 10 feet higher than Tuesday’s level.
FWP officials said during the Tuesday conference call that the next two weeks will tell how much late-season precipitation and spring runoff will flow into the lake. If the anticipated runoff does not occur, they agreed, the Bureau of Reclamation will cut flows into the river to as few as 1,500 cfs and start filling the lake. If runoff picks up to a level that will fill the lake, flows below the dam will remain at 1,900 cfs or more.
At 1,500 cfs, brown trout fry will perish, FWS officials believe. But they were willing to risk low flows later in the spring to ensure survival of the hatching trout eggs for the next two weeks.
All parties agreed to revisit spring precipitation and runoff statistics, lake levels and river flows in May.
- FWP -
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