River bottom may be culprit

October 26, 2013

The eggs of endangered Kootenai River white sturgeon are less likely to hatch on some of the surfaces that have been made more common by human, or anthropogenic, changes on the river, a new U.S. Geological Survey report has found.

The white sturgeon, once common in much of North America, is a very large, slow-to-mature fish that has evolved little from its late Cretaceous ancestors 175 million years ago.

It has great cultural significance for the Kootenai Tribe of Idaho and many other Northwest tribes.

White sturgeon was harvested in many places for caviar, and dams and other development have altered its habitat in ways whose implications are still being studied.

White sturgeon in Idaho’s and Montana’s Kootenai River basin were listed as endangered in 1994, and poor recruitment (the number of a species’ young to survive to maturity) in other West Coast populations is a concern.

"Sturgeons are imperiled across the globe. Our scientists are committed to working with partners, including tribes, to address sturgeon issues across the region," said Jill Rolland, director of the USGS Western Fisheries Research Center.

In the report, prepared in cooperation with the Kootenai Tribe of Idaho, USGS research fishery biologist Mike Parsley and biological science technician Eric Kofoot examined hatch success in the laboratory on various surfaces, such as clean rocks, algae-covered rocks and sand, that sturgeon eggs settle and adhere to in the wild while they develop into larvae.

The scientists found sand to be a poor surface, because the developing sturgeon embryos failed to attach to it. River rocks covered in algae yielded poor results, in part because they were more hospitable to fungus that threatens sturgeon embryos, while waterlogged wood and clean rocks performed well.

The report notes that sand substrates, or surfaces, now dominate the highly altered Kootenai River in areas currently used by spawning sturgeon, and that dam operation for flood management and hydropower during the spawning season have largely eliminated spring scouring flows that typically would clean rocks of algae and other growth.

Finally, the report raises several possibilities, based on the findings, for maximizing white sturgeon recruitment, including substrate-type recommendations for spawning-habitat restoration and the incorporation of scouring flows to clean spawning substrate prior to the spawning season.

"This is another piece in the puzzle of understanding why some white sturgeon populations in highly altered river systems succeed and others don’t," Parsley said.

The publication, "Hatch Success of White Sturgeon Embryos Incubated on Various Substrates," USGS Report Series 2013-5180, by Michael J. Parsley and Eric Kofoot, is available online at http://pubs.usgs.gov/sir/2013/5180.