.png)
Gulkana River Salmon Escapement Sonar Pilot Study
Every summer, thousands of Chinook and sockeye salmon migrate up the Gulkana River to reach their spawning grounds. Understanding how many fish successfully escape the fishery and return to spawn—known as escapement—is essential for sustainable fisheries management.
​
In partnership with the Alaska Department of Fish and Game (ADF&G), AITRC is evaluating the feasibility of using Dual-Frequency Identification Sonar (DIDSON/ARIS) technology to estimate salmon passage in the lower Gulkana River. This pilot study will help determine whether sonar can provide accurate, non-invasive fish counts while expanding long-term monitoring capacity within the watershed.
Why Sonar?
Unlike traditional counting methods, sonar uses high-frequency sound waves to produce video-like images of fish moving through the river. This allows fish to be counted day and night, regardless of water clarity, while minimizing disturbance to migrating salmon.
However, the success of sonar depends heavily on the shape of the river channel. The river bottom must provide a clear viewing area so fish cannot pass unseen beneath or behind underwater features.
Why this spot?
The first phase of this project focused on identifying suitable sonar locations downstream of the Richardson Highway Bridge.
​
Bathymetric surveys were conducted to map the river bottom and evaluate channel depth, slope, and substrate. Suitable bathymetry is critical for accurate fish passage estimates, as uneven bottoms, large boulders, or deep holes can create sonar shadows where fish may pass undetected.
​
The surveys identified several potential monitoring locations with channel characteristics that could support reliable sonar operation.
Why Bathymetry Matters?
A smooth, well-defined river bottom allows the sonar beam to fully image the river channel. Large rocks, steep drop-offs, or other obstructions can block the sonar signal, creating hidden areas where fish cannot be detected.
These blind spots can result in undercounting fish if site conditions are not carefully evaluated before deployment.
Building Future Monitoring Capacity.
This pilot study represents an important step toward expanding fisheries monitoring in the Gulkana River. If successful, a permanent sonar station could provide continuous estimates of salmon escapement, improving fisheries management while supporting Tribal stewardship and long-term conservation of one of the Copper River Basin's most important salmon-producing rivers.
Through collaboration between AITRC and ADF&G, this project combines modern fisheries technology with long-term monitoring efforts to improve our understanding of salmon populations in the Ahtna Territory.
2024 Fisheries Technician, Bailey Roberts, measures the length of a salmon while taking health samples.
Ecologist, Kelsey Stanbro, and 2023 Fisheries Technician, Mia Bobowski, collecting health samples.
Bella Ranck, 2025 Fisheries Technician, joined Kelsey Stanbro, AITRC’s Ecologist, and Morag Clinton, Veterinary Pathologist, for salmon health sample training!
2024 Fisheries Technician, Luke Duvall, taking health samples of the GI tract.