Miles City Fish Hatchery Hosts Prehistoric Visitors
The Miles City Fish Hatchery has played host to some very important and unusual visitors for the past month. Three male pallid sturgeons from the Missouri River in Montana, estimated to be up to 80 years old, have been kept in a large holding tank at the facility. They were brought there so that Montana Fish, Wildlife & Parks can harvest their milt to fertilize eggs, part of the agency's efforts to bolster this endangered, prehistoric species. Hatchery reproduction and stocking of pallid sturgeon has been an annual event since 1997.
With their elongated snouts and bony armor, pallid sturgeons look something like a small, pale crocodile with fins. The visiting males are several feet long and weigh in the 30-pound range, but pallid sturgeon can exceed six feet in length and top 75 pounds. They are among the rarest and largest freshwater fish in North America.
The three males have changed little from their ancestors that lived about 70 million years ago. What has changed, however, is their habitat. Biologists suspect that dams and other alterations to the river systems have impacted both spawning and larval development. FWP estimates that there may be only about 110 adults left in Montana's wild population inhabiting parts of the Missouri and Yellowstone rivers, so recruitment is a priority.
"We took milt from all three males, and that will go over to North Dakota to mix with eggs to spawn females," said Cory Hagemeister, FWP fish culturist at the Miles City Fish Hatchery.
Milt is the term for seminal fluid from fish. In the wild, sturgeon spray the fluid onto roe, or eggs, deposited by the females in large numbers on rocks or hard surfaces. Females swim upstream to spawn between May and July, but they only spawn every two to three years on average. Once eggs are fertilized, the larvae drift back downstream for up to two weeks while they develop. Relatively few survive to adulthood because females are not able to spawn far enough upstream before the larvae drift into an oxygen-deprived zone at the headwaters of Lake Sakakawea in North Dakota. If the larvae do survive, the males won't reproduce until about 10 to 15 years of age, and the females 18-20 years.
The hatchery staff had two mature males lined up to harvest milt, but they were pleasantly surprised when another became available.
"The third male was caught by a 10-year-old girl while paddlefishing" at Intake Fishing Access Site, Hagemeister said. Crews were out looking for sturgeon, so the fish was brought to them and then sent to Miles City.
"He hadn't been seen since '97 in any of the spawns," Hagemeister said.
They identified the sturgeon using his electronic PIT tag. All three males are also carrying radio transmitters.
Once the milt from Miles City is mixed with the eggs at Garrison Dam National Fish Hatchery in North Dakota, the fertilized eggs will return to Miles City. The eggs will represent nine different family groups to aid in genetic diversity, and the target for release is 300 fish per family group. By next summer the fish should be six to eight inches long, ready to release into the Missouri River in Montana. The North Dakota hatchery's remaining eggs will be used in a larval drift study on the Missouri River downstream of Fort Peck Dam taking place this summer.
"They are an interesting fish," Hagemeister said of his work with the pallid sturgeon. "I like it a lot."
With the males' jobs done - for now – they were transported and deposited back into the Missouri River Thursday. If the two hatcheries' efforts are successful and Mother Nature cooperates, a cycle that has been going on for millions of years will continue.
The pallid sturgeon is just one of several fish that the local hatchery works with in its main building and 49 ponds. The hatchery was also preparing walleye fingerlings for release last week. The facility's seasonal target is to raise 10 million walleye fry and one million fingerlings. Another tank was full of tiger muskie measuring over a foot long. The tiger muskie is a sterile hybrid between a northern pike and a muskellunge. FWP raises it for stocking to clean up ponds. Other guests at the hatchery include smallmouth and largemouth bass, channel catfish and occasionally sauger and shovelnose sturgeon.