WILLISTON, N.D. — Then there were four.
That’s the number of endangered adult pallid sturgeon that the U.S. Fish and Wildlife Service was searching for last week as crews drifted trammel nets on the lower Yellowstone River in an attempt to capture and hold a few of the fish for spawning.
“We’re trying to capture the genetics, now, of all of the adults,” said Ryan Wilson, USFWS biological technician for the Pallid Sturgeon Recovery Program.
As easy as netting a fish may sound, the Yellowstone is a big, broad river. In four days of netting last week, the six crews captured 15 pallid sturgeon, three of which were kept for spawning — two males and a female. The crews will return later this month in an attempt to capture the genes of the last remaining unspawned fish, as well as to track fish movements and their use of the river.
The results of their harvest last year is the successful spawning of 1,000 12-inch pallid sturgeon that will be stocked this spring in the Missouri and Yellowstone rivers.
Decades of work
Since 1996, the U.S. Fish and Wildlife Service, with the assistance of the Montana Department of Fish Wildlife and Parks, has captured about 255 fish in the lower Yellowstone River and on the Missouri River between Fort Peck Dam and North Dakota’s Lake Sakakawea. Another population of two wild pallid sturgeon are all that remain above Fort Peck Reservoir in the Missouri River, cut off from the lower reaches by Fort Peck Dam. That tiny population has been supplemented by stocking, as well, with a 2012 sampling showing 336 pallids.
Interestingly, none of the 255 pallid sturgeon that have been captured were siblings, and all of them are presumed to have been born prior to 1955, when the dam creating Sakakawea was completed. It is predicted that the adult wild sturgeon may all be dead in only four years.
Since the dam was erected, there has been no documented wild pallid sturgeon that has been born and lived for one year upstream of Sakakawea. Out of the 255 wild pallids that were once known to live in the sections of the Yellowstone and Missouri, only about 100 are still alive, making the fish one of the rarest species in North America. The fish, a relic of the dinosaur era with relatives found in the fossil record 70 million years ago, were listed as an endangered species in 1990.
“Basically, we’ve used up all of the existing adults,” Wilson said. “Now we’re catching the same fish.”
Diary of a pallid
As the USFWS’s heavy aluminum boat motored loudly up the Yellowstone River last Thursday morning, Wilson stood in the bow looking ahead, holding onto the railing for support. At his feet laid a plastic buoy and a pile of drift net. Behind the bow of the boat was a large galvanized tub that could be filled with river water if a sturgeon was captured.
“We’ve been doing this 15 years and we still don’t know where the fish are,” Wilson said. “We know where they are in general, but not specifically.”
Fish that are captured are scanned for a microchip. An alpha-numeric number that is unique to each fish that has been tagged shows up on a scanner. From the number the fisheries crew can figure out if the fish has been spawned before, where and how many of its progeny were stocked, as well as where and when it was last captured.
Over half of the adults in the river also have radio tags surgically implanted in their stomachs, allowing FWP to generally locate fish with a receiver. Two antennas set up along the Missouri and Yellowstone also track when the fish pass, giving the fisheries crew some idea of where and when fish have moved.
Egg, sperm banks
If a netted pallid sturgeon hasn’t been spawned – which is happening less and less as time goes on – it’s trucked three hours southeast in a 700-gallon, covered fiberglass tank to Garrison Dam National Fish Hatchery in Riverdale, N.D. Once there, the hatchery staff may induce egg laying if it’s a female, or to capture sperm if it’s a male. After spawning, the adults are released back into the river in July.
A female sturgeon can produce about 100,000 eggs, the bigger the fish the more eggs they will produce. Some sturgeon weigh around 60 pounds and stretch to 6 feet long. One male caught last Thursday must have been the runt of the litter. He weighed only 15.4 pounds and measured 44.4 inches.
“This is probably the smallest adult wild pallid we’ve caught,” Wilson said.
The females only spawn every three years, the males every one to two years.
By fall, the hatched pallid sturgeon raised in the hatchery can measure 9 inches long. By the following spring, they’ll stretch 12 to 14 inches, a size at which they are unlikely to be eaten by other fish when they are planted back into the rivers.
Of the hatchery-born pallids that have been released into the Missouri and Yellowstone rivers starting in 1998, not one has yet become sexually mature — 16 years later. Of the fish the same age that have been kept in the hatchery as brood stock, as a backup in case anything should happen to the stocked fish, they were mature at 9 years old.
“The biggest ones we have stocked are now over a meter long,” Wilson said. “The growth is slower than we expected, but that’s based on other sturgeon species like the white sturgeon, which are bigger.”
There are two methods that could help pallid sturgeon successfully reproduce in the Yellowstone and Missouri rivers.
One is being examined right now by the Army Corps of Engineers. The agency has outlined a plan to build a winding side channel around the Intake Diversion Dam on the Yellowstone River. The idea is to allow pallid sturgeon to swim farther upstream to spawn because when their eggs hatch, the larvae drift downstream. The farther upstream the fish can get, experts have theorized, the better chance the larvae won’t end up in Lake Sakakawea in North Dakota where they are eaten or die.
The other option is to mimic spring runoff by dumping more water through Fort Peck Dam on the Missouri River. In 2011, record high runoff prompted dam officials to release a record amount of water from the dam, mimicking what the river’s runoff may have been like before the dam was constructed. Spring runoff helps trigger the sturgeon to spawn, prompting them to run upstream. Pallid sturgeon were documented swimming up the Missouri and successfully spawning.
Biologists believe that 2011 proved that releasing pulses of water into the Missouri — 20,000 to 25,000 cubic feet per second — in the spring could entice pallid sturgeon to swim up the river and successfully spawn.
“It seems like there’s a lot to gain by increasing the flows from Fort Peck Dam,” said Dave Fuller, a Montana Department of Fish Wildlife and Parks fisheries technician. “In 2012, juvenile fish moved up the Missouri to the base of the dam, but now with the water clear and cold they’ve moved out.”
No more new genes
Even after all of the targeted pallid sturgeon are captured and spawned to preserve their varied genetics, Wilson and his crew’s work will continue. They will still return in the summer to net fish as a way to track survival of the planted fish, as well as to determine where the fish move at different times of the year. And they’ll keep searching in hopes of finding a young wild fish, one born from successful spawning that occurred in the Missouri River in 2011.
Because of heavy stocking of the first pallid sturgeon progeny that were raised in hatcheries, which was later cut back to ensure there were fish from a variety of adults, one concern biologists have is that there might not be enough habitat to support all of the planted pallids.
More than 1 million pallid sturgeon fry, fingerling and yearling pallids were stocked in the Missouri and lower Yellowstone in the first 12 years of the program.
“There’s probably not enough available habitat to keep all of the progeny going,” Fuller said. “We started cutting back stocking and talking to geneticists to see what we’re doing here.”
So for now, it’s up to the fish and the rivers to decide how many of the fish survive, but it’s likely up to humans to figure out if they can provide a way for the fish to successfully reproduce in the wild.
“We have them in the river,” Wilson said. “They are surviving. The question is whether they will reproduce.”