Idaho Study Finds Whitefish Declines in Certain Rivers

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A recent study by the Idaho Department of Fish and Game has found that while mountain whitefish populations are generally stable or increasing across much of the state, certain rivers and streams are experiencing declines. The study reviewed decades of snorkel survey data and conducted updated field surveys, identifying the South Fork of the Clearwater River and smaller streams as areas of concern. Biologists also documented reductions in whitefish numbers in larger rivers wider than 100 feet. The department is now funding further research to investigate the potential causes of these localized declines.

Why it matters

Mountain whitefish are a native and prolific salmonid species in Idaho, commonly encountered by anglers fishing for trout. The findings of this study highlight the need for continued monitoring and research to understand the factors impacting whitefish populations in certain regions, in order to ensure the long-term health of this important fish species.

The details

The Idaho Department of Fish and Game recently completed two studies examining mountain whitefish trends across the state. The first study reviewed decades of snorkel-count data collected in the Salmon and Clearwater river basins, finding that most mountain whitefish populations in those basins have remained stable or increased since the mid-1980s, with the exception of the South Fork of the Clearwater River where declines were observed. The second study focused on the upper Snake River basin and areas near the Oregon, Nevada and Wyoming borders, re-surveying dozens of streams previously surveyed in the late 1990s and early 2000s. While whitefish remain abundant in many locations, biologists documented declines in smaller streams less than 60 feet wide, as well as in larger rivers wider than 100 feet.

• The first study reviewed decades of snorkel-count data collected in the Salmon and Clearwater river basins since the mid-1980s.
• The second study focused on surveys conducted between 2020 and 2024, re-surveying dozens of streams previously surveyed in the late 1990s and early 2000s.

What’s next

The Idaho Department of Fish and Game is funding a University of Idaho graduate student to investigate possible causes of the whitefish declines, including changes in distribution and abundance.