Pallid Sturgeon Puzzle: Fisheries Crew Working to Put all the Recovery Pieces Together

Photo credit FWP For many reasons, 2023 was the “Holy Grail Year” for Montana Fish, Wildlife & Parks’ pallid sturgeon recovery efforts in the Yellowstone River drainage. That’s fisheries manager Mike Backes’ term for it. Fisheries crews were able to validate the spawning of two wild heritage females with a wild heritage male and an unknown male in the Tongue River after capturing larvae that matched the parental genetics from three of the fish. For the endangered pallid sturgeon, successful spawning in the wild hadn’t been documented in Montana in at least 30 years, so this was a major breakthrough. Time will tell whether the larvae from those spawns will survive to adulthood, but 2023 marked a promising start. “Beginner’s luck,” Backes calls it now. This summer, fisheries staff spent weeks intensively monitoring the same three wild pallids in the Tongue River using radio telemetry. As in 2023, these three fish initiated their spawning migration from the Missouri River, beginning near Williston, N.D. Ultrasound showed both females were full of eggs. In the end, however, neither female deposited eggs for fertilization before heading back downstream. Backes doesn’t know why the females didn’t spawn, but one difference he noted is that Tongue River flows in 2025 were less than 1,000 cubic feet per second, while 2023 flows ranged from 2,500-3,000 cfs. While crews were monitoring these pallids in the Tongue, another wild heritage female never used for spawning and three genetically high-priority males were brought to the Miles City Hatchery to spawn. It’s part of the pallid stocking and recovery program, which began in 1997 to augment wild populations with hatchery-reared yearlings in the Yellowstone and Missouri rivers. “Finding this new female that could be more than 60 years old, and possibly never touched by human hands, was extremely rare,” Backes said. Wild female code 297, as she was dubbed, was a very welcome addition to spawning efforts at the hatchery. On June 13, she did her part, releasing more than 88,000 eggs. Her eggs were combined with milt from one wild male and sperm from other wild males that had been cryogenically preserved. The process was overseen by Miles City Fish Hatchery Manager Cory Hagemeister, Miles City fish culturists Josh Culver and Larry Bennert, and Jason Ilgen, federal fish biologist at Gavins Point National Fish Hatchery in Yankton, S.D. FWP and U.S. Fish & Wildlife Service coordinate on pallid recovery efforts. This is the second year they have conducted hatchery spawning together, sharing labor and embryos to help diversify populations in both states. Last year, the spawning was done at Gavins Point, and Ilgen brought some embryos to Miles City to hatch. Ilgen has worked with pallid sturgeon for almost 20 years, 18 in Montana, and has collaborated with FWP on a variety of fisheries projects. Backes has worked with pallid sturgeon for most of his 30-plus-year career. Both had high expectations for this spawning, but a little over a week later they learned the bad news: None of code 297's fertilized eggs had hatched. “We had high hopes,” Hagemeister said. “Everything that we know to check looked good. As the date that the eggs should hatch came and went, I hoped that they were just late, but I know it isn’t the way it works. That date is based on temperature, and the development of the egg will happen. Something failed to work in the egg during the development of the larval fish.” “It was heartbreaking,” Ilgen said. “I wanted to justify all the hard work put in by the field crews, geneticists and hatchery staff by producing some healthy fish to stock in the river.” By all appearances, the complex spawning process had gone well. Ilgen’s excitement was palpable that day as he and Hagemeister watched cell division take place inside the eggs, projected from a microscope onto a computer monitor. “We’ve got fertilization,” Ilgen said as he tapped the screen and counted viable embryos. In fact, there was a more than 90 percent fertilization rate in the five groups of eggs checked. “It went so smoothly, I thought nothing could go wrong,” Ilgen said. “In the end, though, I was reminded of the reality of working with pallids: There are no guarantees.” It’s not known yet why the eggs didn’t hatch, but that will be another avenue to explore as their work continues. “We’ve had years where they hatch out, they might be a week old, and they all die,” Hagemeister said. “You could lose them all one day, or one night.” “It’s interesting, and it’s definitely a challenge to work with sturgeon,” he said. “Each species of fish presents a unique challenge to propagate, but sturgeon is just quite a bit different than most of the others.” There’s still a possibility that spawning occurred in the wild with untelemetered fish - wild unknowns or hatchery fish reaching sexual maturity - but for this season Backes and his crew have done all they can. There’s plenty of data to compile for 2025, and then they will need a new game plan for future years. “We’ll learn what we can from 2025 spawning events at the hatchery and in the Tongue River,” Backes said, “and in 2027 the same three females will be on our priority list to monitor.” Females only spawn every two to five years, and they take 15 to 20 years to reach sexual maturity. “The good thing is, we can try to spawn this female again in two or three years, hopefully with better results,” Ilgen said. “My goal is continuous improvement of spawning and rearing practices. I feel that if we are going to go through these propagation and stocking efforts, we should produce the most river-ready sturgeon possible.” “We’ve got so many fish to raise that you don’t really have time to dwell on it too long,” Hagemeister said. River monitoring will continue, along with the stocking program at the hatchery, where significant strides have been made. To date, 20,000 yearling pallids representing 14 different age classes and multiple genetic lines have been successfully stocked by hatcheries in the Yellowstone and Missouri rivers. Some of the oldest age classes are reaching sexual maturity, and a handful of fish have been observed making upstream runs during the spawning window. The goal has always been for pallids to resume natural spawning and recruitment in the wild. With completion of a bypass channel at Intake Diversion Dam on the Yellowstone River in 2022, pallid sturgeon now have access to upstream reaches and the Tongue and Powder River tributaries. Sadly, there are estimated to be fewer than 100 wild heritage fish left in this system, and many are nearing the end of their lifespans, Backes said. Even with a bypass channel, natural spawning and recruitment is far from guaranteed. There must be adequate river flows and water temperatures to trigger migration. Females and males must coordinate their runs. Spawning must occur far enough upstream to allow for larval drift and development before they drift into the anoxic (no-oxygen) zone at the bottom of the river at the headwaters of Lake Sakakawea in North Dakota. Fertilization needs to occur, the embryos need to hatch, and the larvae must settle out in the river to survive and recruit into the population. “Much has been learned, but there are still many unknowns,” Backes said. In 2023, all the puzzle pieces fell into place for pallid sturgeon; now it’s a waiting game to see when it might happen again with wild heritage adults, or with the increasing number of sexually mature hatchery fish released in the river, or both.