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Muggli Bypass Unique & Beneficial Project for Fish

Fishing - Region 7

Wednesday, March 30, 2011

The Tongue River is a major source of irrigation water for farms and ranches that lay along its boundaries. It’s a tributary of the Yellowstone River and provides aquatic habitat for numerous species of warm-water fish. Several diversion dams were built on the Tongue to divert water for irrigation; this has provided stability for agricultural production along the river course. As a long-term consequence of these dams, historic fish passage, annual spawning runs and fish distribution have been interrupted.
Construction of a fish bypass at the base of the historic T&Y Diversion Dam on the Tongue River has allowed opportunity for fish passage and continued water diversion for irrigation. The fish bypass project was designed to operate independently from the established irrigation system. The project was named “Muggli Bypass” after Roger Muggli, the manager of the T&Y Irrigation District. Muggli oversees the operation of the irrigation system at the dam and has provided extensive effort in the project development. 
The bypass was constructed in 2007 with funding and technical support from a variety of sources including: T&Y Irrigation District, Montana Department of Fish, Wildlife and Parks (FWP), The Nature Conservancy, U.S. Fish and Wildlife Service, Natural Resources Conservation Service and the Bureau of Reclamation. 
The bypass was built to allow fish in the Tongue River to move beyond the diversion dam and to re-establish fish movement upstream throughout their historic range. Fish biologists have taken advantage of this opportunity to assess the relative abundance and species of fish in the Tongue and to evaluate the changes in fish populations above and below the dam over time. 
FWP began monitoring fish movement through the bypass in 2008 to determine if the bypass provided the means for fish to move around the dam and into the upper reaches of the Tongue River. The passage was monitored for a 24-hour period each week from late March to mid October. A fyke net was placed at the top of the bypass to capture all fish that made it completely through the bypass channel during the 24-hour periods. 
During the 2008 study, 4,761 fish representing 11 native species—19 species in all—were captured in the fyke net, indicating success in navigating the bypass. Four species in particular—goldeye, freshwater drum, western silvery minnow and smallmouth buffalo—had not been observed upstream of T&Y dam since the turn of the century. It was estimated that 35,000 fish successfully navigated the bypass during the monitoring period.
            In 2009, identical monitoring methods were repeated from March to September and 2,985 fish composed of 20 species were caught in the fyke net.  An estimated 20,880 fish made it through the bypass during the study period. The most plentiful species to successfully navigate the bypass were goldeye and western silvery minnow.  Overall number of goldeye using the bypass was considerably higher than in 2008. Collectively these two species composed 54% of the total number of fish that used the bypass. Other common species included flathead chub, shorthead redhorse sucker and channel catfish. 
            In 2009, Yellowstone River sauger were also observed upstream of T&Y dam, this was the first documentation upstream of the dam since its construction over 120 years ago. Goldeye, freshwater drum and bigmouth buffalo were observed just below Tongue River Reservoir, indicating they swam the entire 160 river miles from the bypass to the base of Tongue River Reservoir Dam. The bypass has provided additional opportunity and environment for many species to spawn upstream on the T&Y Dam.
            Concurrent with the fyke net study, electro-fishing (another sampling technique) was conducted in the Tongue River downstream of T&Y Dam and in other parts of the river so general fish numbers could be compared with the corresponding number of fish that used the bypass. Generally, periods of high-water flows provide a more ideal environment for fish movement, causing a potentially greater number of fish to swim into the Tongue River from the Yellowstone River. Fish sampling revealed that the number of fish making their way through the bypass was higher during periods of increased river flows.  Accordingly, fish numbers declined in proportion to decreased flows.
            The only common species found downstream of T&Y Dam not observed upstream during 2008 and 2009 was shovelnose sturgeon. Biologists believe this was likely due to high water velocities in the bypass channel coupled with attraction problems created from a large back eddy that formed at the mouth of the bypass. The bypass entry from the Tongue River laid perpendicular to the base of T&Y Dam. During high river flows, when sturgeon were present, the increased velocities spilling over the dam created the eddy. The eddy seemed to hamper the ability for some species to find the bypass entry way. Abundant species like goldeye were less efficient at using the bypass because of the eddy.  April 2010, the lower third of the bypass was re-sloped and the channel entrance was moved downstream about 20 feet to eliminate the large eddy. Acting Fisheries Program Manager, Mike Backes has overseen the study and evaluation of fish passage. He noted that other biological factors may come into play for shovelnose sturgeon, despite the opportunity of passage. Backes said, “As a long-lived fish, up to 50 years, shovelnose sturgeon have been spawning downstream of T&Y Dam for many years.  They know how far they have been able to swim upstream and they may not have the instinct or desire to go beyond the dam.” 
Although it may not take place on a yearly basis, FWP will continue to monitor fish passage through the bypass in order to evaluate the long-term impacts for fish in the Tongue River. Electro-fishing will be employed upstream of the dam to determine how species such as shovelnose sturgeon progress in utilizing the bypass.
The bypass has created a biological and environmental connection between the lower and upper reaches of the Tongue River. “It has been very successful for many species of fish,” said Backes. “Some have used the entire 160 additional river miles that have been made available to them.  There are also several tributaries that flow into the Tongue River above the diversion dam that they now can use as habitat.”