SPOKANE — The eggs of endangered Kootenai River white sturgeon in Idaho and Montana are less likely to hatch in the river because of flow changes caused by Libby Dam and other human actions, according to a new report by the U.S. Geological Survey.
The report issued this week concluded that sturgeon eggs hatch best in places where rocks are washed clean of algae by river flow.
The report, prepared in cooperation with the Kootenai Tribe of Idaho, examined hatch success in the laboratory on various surfaces, such as clean rocks, algae-covered rocks and sand. Sturgeon eggs settle and adhere to those surfaces in the wild while they develop into larvae.
The scientists found sand to be a poor surface, because the sturgeon embryos failed to attach to it.
River rocks covered in algae also yielded poor results, in part because they were more hospitable to fungus that threatens sturgeon embryos, the study found.
But clean rocks and waterlogged wood produced good results for the eggs, the report found.
“This is another piece in the puzzle of understanding why some white sturgeon populations in highly altered river systems succeed and others don’t,” USGS fishery biologist Mike Parsley said.
Sandy surfaces now dominate the Kootenai River in areas currently used by spawning sturgeon, the report found.
Meanwhile, dam operations for flood control and hydropower during the spawning season have largely eliminated spring flows that typically would scour rocks of algae and other growth, the report said.
The report suggested that the survival of young white sturgeon could be improved by increasing scouring flows to clean rocks prior to the spawning season.
The white sturgeon was once common in much of North America. It is a very large, slow-to-mature fish that has cultural significance for the Kootenai Tribe and many other Northwest tribes.
White sturgeon was harvested in many places for caviar, but dams and other development have altered its habitat in ways that are still being studied.
White sturgeon in the Kootenai River basin were listed as endangered in 1994. Poor survival of young sturgeon in other places is also a worry.
“Sturgeons are imperiled across the globe,” said Jill Rolland, director of the USGS Western Fisheries Research Center.
Before the construction of Libby Dam in northwestern Montana in 1974, there were an estimated 10,000 Kootenai River sturgeon. Fewer than 500 mature adults of spawning age remain.
The wild Kootenai River white sturgeon is a toothless beast from the days of dinosaurs. It has a large head, armor-like scales, can reach 19 feet long and top 1,000 pounds. It takes 20 or 30 years for white sturgeon to reproduce.
An isolated population of the bottom-feeding behemoths lives along a stretch of the Kootenai that passes through Montana, Idaho and British Columbia, Canada.
Officials have said survival of young sturgeon in the river appears to be nonexistent. The tribes have a hatchery program that produces sturgeon and puts them in the river to prevent the population from becoming extinct.