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Dr. Pat Braaten |
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Dr. Pat Braaten is a Research Fish Biologist for the US Geological Survey, Columbia Environmental Research Center, stationed in Glasgow, Montana. His research concerns the federally-endangered pallid sturgeon.
Q: Pat, most Montanans probably consider themselves somewhat knowledgeable about the fish of our state, but not many of us are familiar with sturgeon. Where do they occur in Montana?
A: Three species of sturgeon can be found in the river systems of Montana. A federally-endangered population of white sturgeon occurs in the Kootenai River. The shovelnose sturgeon, which is relatively common, lives in the Missouri River upstream and downstream from Fort Peck Dam, in the lower Yellowstone River, and as a resident or seasonal inhabitant of tributaries such as the Marias, Milk, Powder and Tongue Rivers. The pallid is the third sturgeon species found in Montana, and the main focus of my research. In Montana, estimates suggest there are 40-50 wild pallid sturgeon remaining in the Missouri River upstream from Fort Peck Reservoir, and 100-150 between Fort Peck Dam and Lake Sakakawea in North Dakota, including the lower Yellowstone River.
Q: You made reference to "wild" pallid sturgeon – are there fish that aren't wild?
A: Most Montanans will likely never encounter a wild pallid sturgeon due to their low numbers, but fishermen may catch hatchery-raised juvenile pallid sturgeon. Thousands of juveniles have been stocked in the Missouri and Yellowstone Rivers over the last decade to replenish the wild population. In most instances, anglers can tell if the sturgeon they caught is a hatchery-raised fish by looking at the underside of the snout. Most hatchery fish are marked there with colored elastomer (an elastic bio-compatible plastic) injected in the skin. The color and orientation of the mark tell biologists which year the fish was spawned in the hatchery and where it was released. After they examine their catch, anglers must immediately return any pallid sturgeon back to the water.
Q: When we read about sturgeon, they're always referred to as "ancient fish." Why is that?
A: Modern-day sturgeons belong to a group of fishes that have been around for a very long time. The early ancestors of modern pallid sturgeon likely originated 60–80 million years ago - they were swimming in the waters of North America when dinosaurs roamed the continent. Plus, sturgeons have physical characteristics that distinguish them from more recently-evolved fishes. Instead of scales, they have rows of scutes - bony plates - on their backs and sides. This external armoring is common among ancient fishes. The tails of some species, like the shovelnose and pallid sturgeon, are heavily armored, and the bellies of some species have hardened plates. All sturgeons exhibit the primitive characteristic of having a skeleton made of cartilage rather than bone.
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| Dave Fuller, Montana Fish, Wildlife and Parks, with a wild pallid sturgeon. |
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Q: Is it true that they can live many years, and grow to be very large?
A: That's true. Although pallid sturgeon are only about a third of an inch long at hatching, adults in the upper Missouri basin can exceed 39 inches, and they typically weigh 35-60 pounds. Individuals weighing more than 80 pounds have been reported. Estimating ages of these large fish can be challenging, but we're confident the largest pallid sturgeon found in Montana are at least 40-50 years old, very likely older.
Q: Why is there a research program dedicated to pallid sturgeon?
A: The historic distribution of pallid sturgeon includes the Missouri River all the way from Montana to the mouth of the river, the middle and lower reaches of the Mississippi River and the larger tributaries of these rivers. Today, pallid sturgeon are still found throughout much of this range, but numbers of wild fish are greatly reduced, the species has been extirpated in some areas and there's little evidence of natural reproduction and recruitment. Pallid sturgeon are in danger of going extinct, and we need to know much more about their biology and how they operate in their environment to keep that from happening.
Q: Why are they in danger?
A: There are several factors that arise from human modification of river systems. The construction of dams alters the natural flow regime, temperature regime and habitat processes of rivers, and dams themselves block fish migrations. Reservoirs have inundated much of the natural riverine habitat used by pallid sturgeon, and channelization of the lower Missouri and Mississippi rivers has altered the aquatic habitat. Commercial harvest and pollution may also be factors.
Q: What are the general goals of pallid-sturgeon research?
A: First, we need to understand the biology and ecology of the species in order to develop and test management actions that could improve populations. So, one set of studies focuses on pallid sturgeon life history: where and when they spawn, what habitats they use for spawning, what happens to young sturgeon after they hatch, under what conditions young and juvenile pallid sturgeon grow and survive, and other basic questions. The other type of research tests pallid sturgeon population responses to restored or enhanced habitat conditions, for example, the effects of improved flow conditions or temperature regimes on spawning success.
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Larval pallid sturgeon. |
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Q: What does your own research involve?
A: For the last 11 years, I've been conducting fundamental and applied research on pallid sturgeon in the Missouri River between Fort Peck Dam and Lake Sakakawea, and in the lower Yellowstone River. The Missouri River downstream from Fort Peck Dam is hydrologically altered, and the water temperature is cold as a result of cold-water releases from the reservoir. Both the flow and temperature alterations diminish the suitability of the river for sturgeon spawning and recruitment. In contrast, the flow and temperature regimes in the Yellowstone River are nearly natural. I, along with colleagues from Montana Fish, Wildlife and Parks, have been examining movements and spawning migrations of pallid sturgeon in both river systems, and determining if, when, where and to what magnitude spawning is occurring. To do this, we surgically implant radio transmitters in wild adult pallid sturgeon, then follow and relocate individual fish throughout the spawning season. Our second line of research focuses on the early-life-stage ecology of pallid sturgeon, specifically the period from hatching through the first year of life. This research indicates that pallid sturgeon larvae naturally drift in the river currents for several days, and may be carried hundreds of miles downstream. This long-distance drift provides a possible explanation for the lack of survival and recruitment of pallid sturgeon in this portion of the Missouri and Yellowstone Rivers. Because of river fragmentation from dams and reservoirs, there may not be adequate length of riverine habitat necessary for the drifting life stage.
Our recent work has examined the migration pathways of pallid sturgeon in the Yellowstone River. Besides radio telemetry of fish, we make use of a variety of technologies, including an acoustic Doppler current profiler, side scan sonar and DIDSON (an underwater acoustic camera). Our goal is to define the hydraulic and habitat attributes that are used and avoided by pallid sturgeon during upstream migrations.
Q: How could water managers apply your research findings?
A: Both management of existing water-control structures and design of new structures can incorporate the research findings to help restore pallid sturgeon populations. Research results have indicated that increased flows and warmer water would improve conditions for sturgeon. Experimental releases from Fort Peck Dam have been proposed to test this hypothesis. In the Yellowstone River, a major habitat restoration project is being implemented in the reach affected by the Intake Diversion Dam. The dam will be modified or replaced to facilitate upstream passage by pallid sturgeon and other native fishes, and the design of the new structure will incorporate research findings to optimize conditions for fish passage. The goal is to enhance the pallid sturgeon population by increasing access to upstream spawning areas and providing larval sturgeon with more drift distance after hatching. |
