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The pallid sturgeon is sometimes called "the dinosaur of the Missouri River."
With its long, flat snout, a few rows of bony scales, and a growth potential of seven feet, it certainly looks prehistoric. And in fact, the species descends from fish that inhabited the Missouri and Mississippi rivers 70 million years ago.
Today, biologists are struggling to keep the endangered fish from going the way of the dinosaurs.
On Nov. 1, biologists with the U.S. Fish and Wildlife Service released several hundred young, nine-inch pallid sturgeon into the waters of the Big Muddy, near Booneville, Mo.
The fish were spawned at the Miles City, Mont., State Fish Hatchery and subsequently raised at the Service's Neosho National Fish Hatchery in southwestern Missouri, with financial support from the U.S. Army Corps of Engineers.
The recent release is one in an ongoing series of stocking efforts throughout the Lower Missouri River. Neosho National Fish Hatchery will continue stocking the fish in the Missouri River near Bellevue, Neb.; Vermillion, S.D.; and Booneville (Franklin Island), Mo.
All fish are marked with individually coded tags so their contribution to recovering wild populations can be evaluated over the next 20 years. Transponders will allow biologists to identify each fish and to eventually collect information on movement, distribution, abundance, survival, reproduction, growth, and other life history parameters.
"We are hopeful this is one of many successful stocking efforts as we try to bring this fish back," said Jim Milligan, project leader of the service's Columbia Fishery Resources Office. If efforts ultimately do bring the fish back, pallid sturgeon may eventually become premier game for recreational fishing.
For now, biologists are concerned with conserving the species and restoring it to the ecosystem. With suckerlike mouths, pallid sturgeon feed on numerous other fish inhabitants of the river, serving an important role in the food chain.
But restoring the species will be no quick feat. "Because pallids don't reach sexual maturity until they are between 10 and 15 years old, and the first generation progeny of any stocked fish would require a similar time span to reach maturity, a minimum 20-year time frame is projected to fully assess the situation," Milligan said. "We do know that stocking can only be successful if these fish have the right environment in which to live and grow."
The Missouri River is certainly not the same river the pallid sturgeon's ancestors inhabited 70 million years ago. But most changes have occurred only within the last 100 years as a result of flood control, navigation, and hydropower operations.
"Construction and operation of the six mainstem Missouri River dams completely altered the hydorology of the river ecosystem as well as converting about one-third of the 2,300-mile-long river into deepwater lakes," said Milligan. "Coldwater releases from the dams through hydropower turbines also radically altered the temperature regime. Corps of Engineers' channelization of the lower third (750 miles) of the river for commercial barge navigation and flood control ... also eliminated well over 100,000 acres of the shallow, low-velocity water needed for nursery habitat."
The once large, free-flowing river characterized by turbid water, braided channels, sandbars, and extensive backwater habitats was radically altered. Now, the Upper River is fractured by a series of dams and reservoirs; the Lower River is a steadily controlled channel.
Of all native fish, the ancient pallid sturgeon has perhaps suffered most from these changes. The ratio of pallid sturgeons to all river sturgeons in the Lower Missouri and Middle Mississippi rivers has declined from 1:20 to 1:650 over the last century.
"Because they have stringent spawning requirements," said Milligan, "pallids have had a hard time establishing self-sustaining populations over the past 30 to 40 years."
Scientists think that a rising river level between May and July can trigger spawning runs, but success still requires water temperatures of about 50-60 degrees Farenheit and suitable spawning substrate.
"Good substrate is generally thought to be clean rock, cobble, or rubble on which adhesive eggs will stick," said Milligan. "The rising or high river stage must persist for four to eight days, depending on water temperature, for the eggs to hatch."
The specific challenges to successful pallid sturgeon reproduction do not stop when the eggs hatch. In fact, larval fish are extremely vulnerable because, while absorbing the yolk sac and growing large enough to swim on their own, they drift with the river current for 5 to 12 days. During this time, they can be eaten by just about any other fish who consume zooplankton, and they can be killed in power plants, water supply diversions, or many other types of intake or water-withdrawal devices.
"Drifting larvae are usually lost or killed before they find suitable nursery habitat," said Milligan.
Suitable pallid sturgeon nursery habitat is typically characterized by areas of shallow water that contain firm substrate such as sand, gravel, cobble; by relatively mild water velocities; and by an abundance of plankton and benthic organisms such as worms and bugs on which the young sturgeon can feed.
As the fish grow, so do their chances for survival. They become more mobile; they can tolerate deeper, faster current; and they can move to more suitable habitats as river conditions change.
While pallids have likely been most disturbed, changing river conditions have also made other sturgeon populations wane.
"Shovelnose and lake sturgeon have also declined," said Milligan. "Lake sturgeon is in serious decline, and shovelnose sturgeon populations are in trouble too because they are being severely over-exploited for caviar production."
Adult female pallid sturgeon, which can produce large quantities of eggs, are also considered at risk for caviar harvest. However, such harvest of pallid sturgeon violates federal law.
Pallid sturgeon were designated a federally endangered species in 1990. Recovery efforts have been ongoing ever since. According to Milligan, a combination of stocking young fish, restoring habitat, and reestablishing more natural river flows is essential to pallid sturgeon recovery.
Some stretches of the Missouri River that have been restored to historic conditions have produced dramatic results. In 1998, Fish and Wildlife Service biologists collected wild-born larval pallid sturgeon the first documented reproduction in the Lower Missouri River in at least 50 years from the waters at Lisbon Bottoms, a habitat restoration unit of the Big Muddy National Fish and Wildlife Refuge in Missouri. Managers there created a side channel of the river to mimic an aspect of the river's historic flow pattern.
Several state and federal fish hatcheries in the pallid sturgeon's historical habitat of Montana, South Dakota, North Dakota, Missouri, and Louisiana are engaged in collaborative efforts to produce pallid sturgeon for supplemental stocking.
Norm Stucky, Fisheries Division administrator for the Missouri Department of Conservation said, "the challenge of saving this unique species from extinction is too great for any one agency to assume alone." The Missouri Department of Conservation began rearing pallid sturgeon at the Blind Pony Hatchery in 1992. Since then, more than 10,000 have been stocked in the Missouri and Mississippi rivers.
The latest stock of pallid sturgeon in the river comes from the nation's oldest fish hatchery. Neosho National Fish Hatchery was established in 1888 to produce and stock sport fish, such as rainbow and brown trout. Today, along with its pallid sturgeon efforts, Neosho is experimenting with ways to raise endangered freshwater mussels.
"We're an old hatchery now working to conserve a much older species," said hatchery manager David Hendrix. "We're going beyond the traditional fish hatchery role to help endangered species like pallid sturgeon."
As with the river, the hatchery has changed over time, reflecting the evolving needs of the Missouri River's fisheries. Together, state and federal biologists will evaluate the progress of stocked fish and monitor the recovery of the pallid sturgeon. Biologists estimate that, along with major habitat and flow restoration, supplemental stocking will be required for the next 20 to 30 years ? a tiny measure of time in relation to the epochal span of this prehistoric species.
