Sonar monitoring shows largest Chinook run on Smith River since program began; seals and sturgeon observed

Project biologists reported to the Del Norte County Fish and Game Commission that sonar monitoring on the Smith River produced the largest single-season Chinook salmon estimate recorded by the project: 27,427 fish for the 2024–25 season. The presenter said the program recorded a single-day peak of 3,585 upstream-moving fish on Oct. 27 and a following day estimate of just over 1,800.

The presentation, delivered by the project’s sonar monitoring lead, described how two types of imaging sonar (DIDSON and ARIS units) produce digital imagery used to count and track fish movements. “The advantage of using these imaging sonars is that they can work in dirty water and in pitch darkness,” the presenter said, noting the equipment cannot reliably distinguish species by image alone and therefore uses Rowdy Creek Fish Hatchery trap data to apportion Chinook and steelhead in sonar counts.

Why it matters: the Smith River is monitored at a single downstream site that, the presenter said, captures runs from most spawning tributaries upstream. The commissioner meeting heard that the Chinook total of 27,427 was about 10,000 greater than the project’s average seasonal estimate (average cited as roughly 17,002), while steelhead counts remain below early-project levels and show year-to-year variability.

How the monitoring works and limits: the presenter explained DIDSON and ARIS technology and described trade-offs between range and image quality. He said…