Marias River flows coming out of Tiber Dam in June will increase sharply to see if mimicking nature can help endangered pallid sturgeon reproduce.
The plan, put together by the federal Bureau of Reclamation, Montana State University and Fish, Wildlife and Parks, will push spring runoff out of Lake Elwell, also known as Tiber Reservoir, from 1,200 cubic feet per second to 5,000 cfs in late June then drop slowly.
“The idea,” says Anne Tews, FWP fisheries biologist, “is to see if pallid sturgeon in the Missouri River will respond to the increased flows by swimming up the Marias and spawning. We already know that shovelnose sturgeon, a close relative, respond to increased tributary flows from the Marias.”
Pallid sturgeon evolved with the mountain snowmelt runoff that would swell the Missouri River each spring. With increased river flows, pallids moved hundreds of miles upstream each spring in search of sandy shoals and gravel bars for spawning.
Their fertilized eggs would sink and stick to the river bottom for a few days as the embryo developed. Then, as larva, the tiny creatures would drift downstream for a couple of weeks and, it’s believed, slightly more than one hundred miles until they developed small tails and swam into estuaries and side channels to find food and grow.
Now, the Missouri River upstream of Fort Peck Dam does not have enough free-flowing habitat for the fish to survive. The larval typically drift into Fort Peck Reservoir where they sink and smother. But if they can be induced to spawn in the Marias, the additional miles may help them survive, Tews says.
Starting May 29, flows coming out of Tiber Dam will increase about 500 cfs a day until reaching 4,000 cfs about June 3. The 4,000 cfs rate will remain constant for about a week, then increase to 5,000 cfs by about June 13. The 5,000 cfs flow will remain for 10 days and will result in a river stage increase of about 3.3 feet above the current river level.
Afterward, the flow coming out of Tiber will decrease about 500 cfs each day until it reaches 1,000 cfs about July 1.
In preparation for the increased flows, fisheries biologists have put radio transmitters in 25 pallids and 90 shovelnose sturgeon. The fish will be monitored at stationary receivers on shore, which will tabulate each fish as it swims by.
Many of these pallids are from a release of hatchery raised, 1-year-old fish in 1998, which are just now reaching sexual maturity.
“Because of this year’s high snowpack and potential for increased runoff,” Tews says, “it seemed like a good year to work with an MSU graduate student and try this. The Marias River flows are going to be elevated anyway this year, with this plan they will just come out of Tiber Dam at a higher rate for a shorter period. This is good for native fish.”
(Report by Montana FWP; Feature photo via fws.gov)