Ancient fish poses a mystery

by JIM MANNThe Daily Inter Lake
| June 24, 2009 12:00 AM

BONNERS FERRY, Idaho - Pete Rust lifts a rod attached to a buoy from the waters of the Kootenai River, showing off what is used to monitor movements of white sturgeon fitted with sonic transmitters.

Rust, a biologist with Idaho Fish and Game, says there is a network of 60 these sonic receivers in Idaho from Kootenay Lake to the Montana border.

"These tell us who has been by here," Rust says of the receiver. "Instead of chasing the fish around, we chase these things around."

Data downloaded from the receiver identifies the particular sturgeon that passes by, along with dates and times, which can be cross-referenced with river flow and temperature records.

The tracking system is just part of the effort to solve the fundamental problem of why the river's wild sturgeon population has been dwindling for years.

There are many allies in the sturgeon recovery effort, including the Kootenai Tribe of Idaho, the U.S. Army Corps of Engineers, the Bonneville Power Administration, Idaho Fish and Game, the British Columbia provincial government, the U.S. Geological Survey and Montana Fish, Wildlife and Parks.

There is consensus that Libby Dam has had a significant impact on sturgeon since it was finished in 1972, altering temperatures and flows in a way that has hampered spawning success.

There have been other manmade impacts. The Kootenai River used to meander through a broad flood plain downstream from Bonners Ferry, but over time the river has been hemmed in by extensive levees.

What has complicated efforts to improve spawning success is simply the mysterious nature of the white sturgeon.

"I think what really strikes me is that this is such an ancient fish and we don't know a lot about them," said Brian Marotz, a Montana, Fish, Wildlife and Parks biologist who represents the state on the multi-agency White Sturgeon Recovery Team. "And what makes it mysterious is it cruises through deep, turbid waters so we don't have a lot of information about what this fish did before the dam."

The spawning behavior of a species such as bull trout can be easily observed: Bull trout gather on spawning beds called redds in clear water.

But sturgeon spawning is much more complicated. The main problem on the Kootenai appears to be the failure of sturgeon to move beyond a silt- and sand-bottomed stretch of river below Bonners Ferry into a cobble-and-gravel riverbed, known as the Braided Reach, upstream from Bonners Ferry.

Eggs that are deposited in silt and sand "gum up" and do not survive, Marotz said.

So there have been efforts to get adult sturgeon to move upriver into the Braided Reach, starting with adjusted temperatures and flows from Libby Dam.

For years, the dam released high spring flows for sturgeon, but they were suddenly dropped off. Last year, the spring releases were gradually tapered off into the spawning season - mimicking a natural runoff - with a strong emphasis on gradually increasing river temperatures.

A sonar-tagged sturgeon was tracked nearly 35 miles upstream from Bonners Ferry.

"That's the farthest upriver we've seen a tagged adult go," Rust said.

Water releases that got under way from the dam last week are being managed similar to last year's flows.

"If you asked anybody on the recovery team, they would say that temperature is a big driver" in triggering spawning behavior and a likely influence on how far upriver the adults will go, Marotz said.

Rust's monitoring work on the river has turned up evidence that when temperatures drop, it actually sends sturgeon downriver.

"It doesn't take very much of a drop in temperatures to send them back downstream," he said.

But even with the selective withdrawal temperature control system at Libby Dam, it is difficult to completely regulate river temperatures because of influences such as cloud cover and tributaries far below the dam.

There are other possibilities for the lack of spawning success.

Marotz suspects that sturgeon may becoming 'stock limited" as the number of adult spawners has dropped from about 4,000 in 1990 to the current estimate of about 1,000.

This has to do with the basic biology of sturgeon and the deep, turbid waters they spawn in. Other species, such as bull trout, spawn in clear water on defined spawning beds called redds. But that's not the case with sturgeon.

"Sturgeon just start dropping eggs in the water column and the males have to be in close proximity to release their milt, which is only active four to eight minutes." Marotz said. "It leads us to believe you have to have many males."

When the overall population drops below a certain threshold, Marotz said, there may not be not enough males.

The U.S. Geological Survey is spearheading a program aimed at clearly defining the Kootenai's canyon-like sturgeon habitat, this year deploying a boat on the river with a highly sophisticated 480-channel echo-sounder.

"We're studying the physical habitat," Geological Survey hydrologist Gary Barton said. "We're mapping the elevation of the riverbed from bank to bank."

The mapping system will provide information that will be used to design river restoration projects aimed at improving spawning habitat, particularly in the Braided Reach.

Reporter Jim Mann may be reached at 758-4407 or by e-mail at jmann@dailyinterlake.com