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Marine Salmon Investigations Program

March Freeze-up at Auke Creek Research Station

The key to salmonid research projects at Auke Creek Research Station is the fish counting weir. The Auke Creek weir is made operational each year in early March for counting seaward migrating salmonids leaving the Auke Creek-Auke Lake drainage. The 45-year data set from weir operations provides important information about the freshwater life history stages of seven anadromous salmonid species that migrate in and out of this drainage system. The weir is operated on a cooperative basis with the University of Alaska School of Fisheries and Ocean Sciences (UAF-SFOS) and the Alaska Department of Fish and Game. Both of these agencies conduct specific research projects on one or more salmonid species that migrate through the Auke Creek weir.

Photo of frozen upstream weir pool
The upstream weir pool froze to a depth of at least 30 cm during the March 2006 cold snap. This is only the second time in 27 years that the weir pool has frozen.

The weir is a permanent structure with the capability of capturing all downstream and upstream migrant salmonids and can operate during extreme water flows. During the downstream capture mode the weir is operated to spill most of the stream flow through five horizontal inclined screen traps and four vertical V-shaped panels. The traps and panels are covered with aluminum that has 3-mm perforations. More than 99% of the flow in Auke Creek is spilled through the traps and panels, and all fish are retained. The fish and a small amount of water, about 150 leters per minute, are diverted into a collection trough, through a fish grader, and then into separate holding tanks downstream from the weir. The fish are counted daily and the weir is checked several times a day during changing flow conditions and during peak fish migration times.

The Auke Creek weir was installed in the downstream capture mode in 2006 on 1 March. Stream flow was extremely low, and the weir was operating within a few hours of installation of the last trap structures. Stream flow remained low throughout March, and modifications to the weir were required to keep it working. Two horizontal traps were closed off, and the other three traps were lined with plastic sheeting to stop spillage. The entire flow of Auke Creek was diverted into the fish holding tanks at the weir.

  Photo of ice accumulation on the fish counting weir
An unusual freezing period and associated low stream flows at Auke Creek weir in March 2006 resulted in the massive accumulation of ice on the fish counting weir. Ice was removed daily to keep the weir operational.

Record cold air temperatures near -20C during an unusual 8-day cold spell in mid-March froze the small impoundment pool used to manage stream flow on the upstream side of the weir. Stream temperatures dropped to near 0C, and there was a massive accumulation of ice on the weir traps and holding tanks. It required an hour or more each day to remove the ice from the traps, holding tanks, and inside the trough to maintain water flow.

On 18 March we used hammers and wooden stakes to knock the ice away from the weir traps, thus removing the weight of ice from the structures. A 2-inch pump was used to direct water onto the ice on the weir pool to melt the ice attached to the vertical panels and fish traps. It took several days to complete the ice-melting operation in the weir pool. Despite the unusual icing this year, the weir remained operational and the daily fish counts were maintained.

Usually during March, pink and chum salmon fry dominate the number of migrant salmonids captured at Auke Creek weir, with an occasional Dolly Varden or cutthroat trout captured. In 2006, a total of 1,820 pink salmon fry were counted at the weir through March, considerably less than the average count for March of 10,000. Six Dolly Varden char and one cutthroat trout were also captured in March 2006.

By Jerry Taylor

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