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| Evaluation of Entrainment Losses of Westslope
Cutthroat Trout at
Private Irrigation Diversions on Skalkaho Creek, Montana: Part I |
| Dates: 2002-2005 |
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Background:
|
| Diversion
dam located on Skalkaho Creek. |
Skalkaho Creek is a 40-kilometer long tributary of the Bitterroot River in southwest Montana. The Bitterroot flows 134 kilometers through irrigated farm and ranch land to its confluence with the Clark Fork River near Missoula, Montana. Five major diversions and numerous smaller canals remove water from the river during irrigation season. Many tributaries of the Bitterroot River are also diverted for irrigation during the summer months and contribute little streamflow to the river during that time. Both the mainstem of the Bitterroot River and its tributaries are therefore chronically dewatered during the irrigation season.
Skalkaho Creek supports a healthy population of westslope cutthroat trout (Oncorhynchus clarki lewisi), along with brook trout, brown trout, bull trout, mountain whitefish, redside shiner, and slimy sculpin. This study examined seven lowhead dams on lower Skalkaho Creek that were believed to divert downstream migrant westslope cutthroat trout into irrigation canals. Both post-spawn adults migrating back to the Bitterroot River and juveniles emigrating downstream from nursery reaches of Skalkaho Creek and its tributaries were entrained and became trapped and died in the irrigation canal system, thereby resulting in a net loss to the population. Private landowners and irrigators in the drainage expressed concern over this loss, and collaborated with the research team to help solve the problem. This study has provided beneficial information to project managers regarding the effectiveness of fish screens and the prevention of fish loss due to irrigation diversions. |
Goals:
Provide private landowners, as well as federal/state agencies, with an in-depth evaluation of the value of fish screens to help make decisions on their use and potential value. |
| 1. |
Quantify downstream migrating age-0, juvenile, and adult westslope cutthroat trout entrained at irrigation diversions on Skalkaho Creek, before and after installation of fish screens. |
| 2. |
Evaluate passage efficiency of fish screen structures at irrigation diversions of Skalkaho Creek. |
Abstract:
Post-spawn adult and downstream migrant juvenile westslope cutthroat trout (Oncorhynchus clarki lewisi) are entrained, become trapped, and die in the seven irrigation canals on Skalkaho Creek, a tributary of the Bitterroot River. The research team quantified entrainment rates into the canals using telemetry and trapping before (2003) and after (2004) installation of fish screens at three (Highline, Ward, and Hughes) of the canals to provide private landowners and agency personnel with an in-depth evaluation of the value of fish screens. They also examined the efficacy of the screens in returning downstream migrants to the stream. No telemetered adults were entrained in 2003, but most were residents and therefore did not migrate past the canals. Fifteen telemetered adults were entrained in 2004; three were entrained, bypassed, and entrained again further downstream. Nine telemetered fish were entrained at ditches with fish screens and all nine were successfully bypassed. Only one of 74 telemetered adults successfully emigrated back to the Bitterroot River, by swimming upstream out of a ditch. Five telemetered juveniles were entrained at the Highline Ditch in 2003 and three in 2004, but only one was bypassed. A majority of the 117 telemetered juveniles were residents and therefore did not migrate past the canals. We estimated that 33,722 age-0 westslope cutthroat trout (95% CI, 12,044 to 161,799) moved downstream from July 16 to September 20 in 2003; 8,964 (95% CI, 2,840 to 72,141) or about 27 percent were entrained at the Highline Ditch. In 2004, 7,840 fish were bypassed by all three screens, and of those 6,041 were westslope cutthroat trout. No fish were entrained in two of the three ditches with fish screens in 2004, and only a few fish were entrained in the third. The fish screens effectively precluded entrainment and effectively bypassed adult, age-1 juvenile, and age-0 westslope cutthroat trout. Fish screens were an effective management tool to eliminate entrainment of westslope cutthroat trout at Skalkaho Creek and may also be useful elsewhere to eliminate entrainment of inland salmonids.
Deliverables:
A final report was submitted on December 31, 2004 and provided in the January 2005 WFHI Semi-Annual Report. A Master’s thesis was completed on this project by graduate student, Steve Gale on July 20, 2005. See top of page to download these documents.
Partners:
The study is being conducted in close cooperation with Montana Fish, Wildlife and Parks, local ditch/irrigation companies, and local landowners. |
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|
Vertical flat-plate
self-cleaning screen at Big Creek, Montana. This screen design
is similar to those proposed for
Skalkaho Creek. For a larger view and more information, click
on a photo. |
Graduate
Research Assistant
Steve B. Gale
Montana Cooperative Fishery Research Unit
Department of Ecology, Montana State University-Bozeman
Bozeman, Montana 59717 |
Principal
Investigators
Alexander V. Zale
Montana Cooperative Fishery Research Unit
Department of Ecology, Montana State University-Bozeman
Bozeman, Montana 59717 |
Thomas E. McMahon
Department of Ecology, Montana State University-Bozeman
Bozeman, Montana 59717 |
Collaborator
Christopher G. Clancy
Montana Department of Fish, Wildlife and Parks
1801 N. First, Hamilton, Montana 59840 |
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