Nushagak Weir Projects​​​​​​​​​​​​​​
About​​​
The Nushagak weir projects were started in 2024 as part of BBSRI's Nushagak Chinook Assessment Program.
We operate two fish counting weirs on the Upper Nushagak and Koktuli Rivers, both major Chinook-producing tributaries of the Nushagak river system. ​​​​​​​​​​​​​
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The weirs provide counts of adult salmon migrating upstream to spawn between June 28 and August 15, which covers all of the Chinook run and the majority of the chum and sockeye runs.​​​
Upper Nushagak Weir
The Upper Nushagak weir site is on the upper reaches of the Nushagak mainstem, almost 200 river miles upriver from Dillingham, AK and just above the confluence with the Chichitnok River. ​
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Koktuli Weir
The Koktuli weir site is on the lower section of the Koktuli River, downstream from where the river splits into its north and south forks and just below the outlet of the Swan River. It is approximately 160 river miles from Dillingham.
Weir Design​​​​​
​​​Both of the Nushagak weirs use a fixed panel, tripod design. Steel tripods are anchored in a line across the river, and aluminum panels are rested against them and held in place by water pressure.​​​​​​​​​​​​​ By not fixing the panels in place, they can be easily repositioned or removed and replaced if they're struck by logs or other large debris.
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This row of panels creates a "fish-tight" barrier across the river, so that migrating salmon can only pass the weir when the gates of the livebox are opened.
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Both weirs are also fitted with floating panel "boat gates" which small skiffs and rafts to pass through the weir at any time.
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The weirs are around 180-200 feet long, and use between 20-24 tripods.​​​​
Data Collection
At the weirs, technicians collect three types of data:​​​​​​​​​​​​​
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Passage Counts​
Technicians perform 4-8 hour-long counts per day, counting all the fish that pass through the weir by species.
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Biological Sampling
Once or twice per day, technicians sample Chinook, chum and sockeye salmon and then release them above the weir. Species, sex and length are recorded and scale and tissue samples are taken from each fish.​
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Environmental Data
​Twice per day, technicians record the river stage, precipitation, weather, water clarity and air and water temperatures.
Field Camps
Two technicians live and work at each of our field camps from around June 20 until the weirs are demobilized in mid-August.
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In addition to daily passage counts and sampling sessions, weir crews inspect the weir panels frequently to make sure there aren't any holes that salmon could swim through and to clear off any debris that has floated downriver onto the weir. Occasionally, technicians help rafters, guides, sportfishermen and other boaters pass through the weir if they're not experienced with passing through the boat gate, and have even given tours of the project site to members of the public.
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Our field camps are equipped with solar and gas generated electricity and StarLink satellite internet, which allows crews to quickly transfer data and stay in contact with project managers.​​​​
Why Weirs?
We started the Nushagak weir projects to collect more data about Chinook returns in the Nushagak river system.
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The Nushagak Chinook runs have been declining dramatically in the past 10 years, leading to its listing as a Stock of Concern in 2023.
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We rely almost entirely on ADF&G's Portage Creek sonar project to estimate how many Chinook return to the river each year, but the sonar was proven to be unreliable and inaccurate by multiple studies.
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The Upper Nushagak and Koktuli weir salmon passage data is building a reliable and accurate foundation of data for an independent estimate of Chinook escapement in the Nushagak River.
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As our Chinook Assessment Program expands to include mark-recapture studies, drone surveys, citizen catch reporting and more, the data from these weirs will allow us to create an index of salmon population sizes for the entire Nushagak river system. This will provide another valuable point of reference for managers and regulators overseeing the district's salmon fisheries.
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​For more information, see our 2024 Annual Weirs Report below (in prep.).
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