Wednesday September 27, 2023

Courthouse News Service

Pacific lamprey are making a big comeback at the Bonneville Lock and Dam in the Columbia River Gorge this fall, with returns up 170% from the dam’s previous 10-year average, the U.S. Army Corps of Engineers said Monday.

Army Corps biologists count fish as they migrate through fish ladders at mainstream Columbia and Snake river dams, all of which played a large role in the species’ decline over the last 90 to 66 years.

Since the 1990s, the scientists have worked alongside tribal and government partnerships to improve lamprey passage at the dams — an effort that appears to be paying off, considering as of Sept. 18, biologists counted 63,836 lampreys passing through Bonneville alone.

Overall this year’s lamprey passage represents a 252% jump from Bonneville’s four-year average of 41,414. The number is made all the more impressive given that biologists counted the typically nocturnally traveling species during the day — leading them to suspect this year’s return is a minimum estimate, and the number may actually reach around 165,314.

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