Phys.org details a study carried out on the decline in lamprey numbers:
A new study aimed at understanding habitat needs for Pacific lamprey in western Oregon found this once-abundant fish that is both ecologically and culturally significant prefers side channels and other lower water velocity habitats in streams.
However, because of the legacy of historic land uses in the Northwest – including human settlement and activities – these habitats are much less common than they were in the past. And that may explain why populations of lamprey have declined over the past several decades – not only in western Oregon, but throughout the Pacific Northwest.
“The lamprey decline has probably been going on for the past half century, but it wasn’t until the last 15-20 years that it has been recognized by many in the scientific community,” said Luke Schultz, a research assistant in Oregon State University’s Department of Fisheries and Wildlife and lead author on the study. “Today lamprey populations are at about 5 to 10 percent of the 1960s totals at Bonneville Dam, and the story is much the same elsewhere.
When lampreys are abundant, they reduce predation by a variety of species – especially sea lions, but also sturgeon, birds, bass and walleye – on juvenile salmon and steelhead. It may not be an accident that salmonid numbers have declined at the same time lamprey populations have diminished.
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