Fish on the line 

Pallid sturgeon persevered for 70 million years. Why are they struggling now in Montana?

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The delays had a silver lining, though. They allowed Braaten and Fuller to collect baseline data on the pallid population under normal dam operations, so that when the spills finally came, they would have something with which to compare the fish’s response.

They also began investigating the mystery of the pallids’ missing offspring. By sampling the stomachs of potential predators, they eliminated the possibility that ravenous fish, not dams, were to blame. This brought them to the most popular theory: that the distance newly hatched pallids, or “free embryos,” need to drift while they develop into larvae and gain the strength to swim, and forage exceeds the amount of free-flowing river between Fort Peck Dam and Lake Sakakawea—the vast reservoir that Garrison Dam created downstream. Scientists thought the drifting embryos might be reaching the reservoir’s slack water too early and getting gobbled by lake fish or sinking into the reservoir’s oxygen-poor bottom layers and suffocating.

click to enlarge Missoula Independent news
  • Photo courtesy of Idaho Dept. of Fish and Game
  • The pallid sturgeon's remarkable evolutionary tenacity has been tested through ice ages, volcanic explosions, a mass extinction event and human capture, as evidenced by this historic Idaho Department of Fish and Game photo. But its biggest threat is a series of dams built along the Missouri and Yellowstone rivers.

In 2004, Braaten and Fuller released thousands of hatchery-reared embryos into a side channel near Culbertson, Mont. They followed them downstream and re-collected what they could at different time intervals. The results were deflating. “It looked like even if we got pallids to move up the Missouri, there wouldn’t be enough drift distance to make a difference,” Braaten says.

This new information, however, renewed interest in modifying the Intake Diversion Dam 70 miles up the Yellowstone to allow fish passage, opening up more than 150 miles of new habitat to native fish. If sturgeon used the passage, the added mileage might give embryos enough time to develop before hitting Lake Sakakawea.

In the meantime, Braaten and Fuller examined drift in the mainstem Missouri. In 2007, they released new findings: Immediately after hatching, pallid embryos drift for up to 14 days. Braaten’s models showed that the slowest embryos would travel between 159 and 230 miles before they developed. But there are only about 211 miles of free-flowing river between Fort Peck and Lake Sakakawea. If spawning took place near or in the Milk, a turbid tributary that joins the Missouri 11 miles below Fort Peck, the slowest drifters might settle out of the current before hitting the reservoir. Most, however, would end up smack in the middle of it.

That same spring, Fuller discovered that two females he’d been tracking up and down the lower Yellowstone had spawned—the first documented instances of pallid spawning in the Upper Basin. It was a big step forward, one that allowed researchers to cross spawning off the “reasons-for-recruitment-failure” list.

Later that year, thanks in part to Fuller’s spawning discoveries on the Yellowstone, the pair’s disheartening drift results on the Missouri and the region’s relentless drought, which continued to preclude spills from Fort Peck, the Corps obtained the legal authority it needed to partner with the Bureau of Reclamation to work on Intake, which the Bureau operates. It was a cheaper solution—Intake could cost as much as 10 times less than potential Fort Peck modifications, which are estimated at $500 million—but one that included some controversy. Any money spent on Fort Peck or Intake is money that can’t be spent on recovery and restoration elsewhere on the river—building aquatic habitat in the Lower Missouri, for example. This has angered some downstream biologists who are not convinced that enough wild pallids currently swim all the way to Intake, or spawn in the upper river, for the project to matter much. (Only two or three fish typically make it to Intake each year.) Others believe that even with passage, embryos still won’t have enough room to develop before hitting Lake Sakakawea.

But unlike the Upper Basin populations, Lower Basin fish enjoy access to thousands of miles of free-flowing river, which means no devilishly complicated drift issues. Plus, the Upper Basin’s wild heritage population will almost certainly die out within the decade. This won’t end the species as a whole: Scientists have preserved roughly 90 percent of the Upper Basin pallids’ genetic diversity in hatchery fish, some of which are finally reaching sexual maturity. But unless the drift issue is figured out, their offspring will meet the same fate as their wild brethren: death by reservoir.

Either way, in 2009, the Corps officially terminated Flow Mod. Braaten and Fuller would still share an office and a mission—pallid sturgeon recovery in the Upper Basin—but their research territory shifted. Braaten was assigned to the Yellowstone; Fuller, the Missouri below Fort Peck.

Not long after that, in 2011, the Missouri River Basin experienced a 100-year flood event. Throughout the Upper Basin, record snowpack and spring rains triggered massive runoff. To protect Fort Peck’s structural integrity, the Corps had to release surface water over the spillway. The river raged for weeks.

For Fuller and Braaten, it was an ironic meteorological twist of fate. “We felt it imperative that someone be out there to document the pallids’ response to the record flows,” says Braaten. The crews mobilized: Fuller and his guys on the Missouri, Braaten and his team on the Yellowstone. The huge flows were a stroke of good luck. Getting crews out there, says Braaten, required foresight.

And it paid off. Pallid sturgeon migrated nearly 200 miles up the Missouri toward Fort Peck and the Milk River. “We had never seen that before,” says Fuller. Spring after spring, pallids would leave their wintering grounds below the confluence and swim into the lower Yellowstone. But last year, 16 wild fish went “as high up (the Missouri) as we could have expected them to come.”

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