Endangered Fish’s Breeding Habits Perplex Biologists

Time is running out on the endangered pallid sturgeon, a fish whose ancestors date back 200 million years.

“I’m sure we’re losing fish every year, and we’re not replacing them,” said Mark Dryer, a U.S. Fish and Wildlife Service biologist leading efforts to save the fish. “We haven’t seen any reproduction in the last 10 to 20 years.”

On the endangered species list since 1990, the pallid sturgeon is a throwback to prehistoric times--a gentle, boneless, scaleless fish that can grow to 100 pounds and live 60 years.

It is distinguished by its sucker-type mouth and large whisker-like barbels that hang from its underside to sense its surroundings.

But the fish’s natural habitat has been radically changed in the last few decades. Biologists can find no evidence of natural reproduction.

“It appears we have all adult fish and older fish out there,” Dryer said. “So we need to start reproducing them and stocking them in the wild.”

The total number of pallid sturgeon nationwide isn’t known. The single greatest concentration of the fish is thought to be from 200 to 250 in northwest North Dakota and northeast Montana.

However, trying to gather eggs to grow a new generation in hatcheries has proven as difficult as trying to catch a fish without bait.

Spawning efforts failed in 1994 and 1995 because biologists were still learning about the fish’s idiosyncrasies.

Four separate fishing trips this spring on the Yellowstone River, along the North Dakota-Montana border, landed only six pallid--five males and one female whose eggs were not mature enough.

Unlike most fish, the female pallid spawns only every seven to 10 years.

Runoff from mountain snowmelt has made it too dangerous to continue fishing for at least several months, Dryer said. Biologists must hold nets stretched between boats and float with the current in trying to catch pallid.

“It’s real tricky work when the river flows are so high,” Dryer said.

By the time river flows become manageable again, the spawning season likely will have ended.

Dryer is hoping for better chances next year.

“We’re disappointed we didn’t get the female with eggs we wanted, but the numbers of spawning females with eggs can vary from year to year,” he said.

Other types of sturgeon inhabit lakes and rivers in North America and around the world. But the pallid is unique to the United States, where it roamed the length of the Missouri and Mississippi rivers for centuries.

The fish can appear as friendly as a pet dog. At the Garrison Dam National Fish Hatchery, about 60 miles north of Bismarck, N.D., two males stuck their flattened snouts above water to check on visitors around the tank.

They are called a “bottom feeder” because they suck food from the bottom of the riverbed and spit out the debris.

“Basically, they’ll vacuum the bottom up,” said Rob Holm, assistant manager of the Garrison hatchery. “It’s kind of a neat fish.”

But its normal habitat of turbid, fresh river water has been altered. Dams were built on the upper reaches of the Missouri in the 1950s and ‘60s to control flooding and form lakes. The lower Missouri and Mississippi have been dredged into channels to accommodate barge traffic.

“It’s a whole new world, basically, out there,” Holm said.

Pallids have been found and spawned in the state of Missouri, but biologists believe they may have crossbred with another type of sturgeon called the shovelnose, which is not endangered.

“In Missouri, we come across these intermediate fish that reflect characteristics of both species,” Dryer said.

DNA work is being done to determine the breadth of any crossbreeding and should be completed in about a year.

But biologists are certain that purebred pallids remain in South Dakota, North Dakota and Montana.

“Why we don’t have hybridization is not clearly understood,” Dryer said.

The pallid is most numerous in the Yellowstone and Missouri rivers in North Dakota and Montana because the area has been less disturbed. So that is where efforts to find fish for spawning are being concentrated.

Previous attempts at spawning the fish failed because of timing and water temperature, Dryer said.

In 1994, a female died at the Gavins Point National Fish Hatchery in South Dakota for reasons still not clear.

Last year, at a Montana hatchery in Miles City, the females reabsorbed their eggs before biologists could extract any.

“It’s a real learning process to know when disturbing them causes too much stress, to balance that with checking them frequently enough to know when they’re ready,” Dryer said.

Added Holm, “When working with endangered fish, we don’t want to put any more stress on them than we have to.”

If biologists succeed, eggs will be sent to the Gavins Point hatchery, which is specially equipped to handle endangered species.

But biologists don’t know whether any young pallids will sink or swim in the river habitat.

“If it’s a problem with the habitat, then we’re out of luck,” Holm said. “Who knows what’s going to happen in the next 20 to 50 years? You hate to lose fish that are 200 million years old.”