Adopt-A-Fish update – April 27, 2006
 stitches where a transmitter was implanted and the long antenna. |
while pallids are suffering?
By MATT JAEGER
Montana Fish, Wildlife and Parks
GLENDIVE - Biologists and others working on recovery efforts for the endangered pallid sturgeon are spread far and wide at this time of year. They might be capturing wild adult brood stock fish at the hatcheries. They might be tagging and stocking hatchery-reared juveniles. Or, they might be tracking radio-tagged fish for the Missouri and Yellowstone River Adopt-A-Fish Program.
The amount of effort we put into preserving pallid sturgeon always makes me pause to think about Montana's other sturgeon, the shovelnose, and how subtle evolutionary differences between these closely-related species have resulted in huge differences in the relative number of these fish.
The unique biology of sturgeons allowed them to thrive in the present-day Mississippi drainage for millions of years. Fossil evidence suggests sturgeon have been around since dinosaurs walked the earth as many as 250 million years ago.
But even though sturgeons were resilient and tough enough to persist through ice ages, droughts, climate changes, and continental drift, dams built in just the last 50 years on our large rivers have pushed pallid sturgeon to the brink of extinction. In comparison, Montana's shovelnose sturgeon are doing well.
Why is one sturgeon species highly endangered and another doing just fine?
So far, we've learned that both sturgeons are big movers. Pallids and shovelnose move as much as 150 miles each year during spring and summer months. However, the exact places they move to can be different.
Although both species require river habitats, pallid sturgeon sometimes occupy deeper and slower waters than shovelnose sturgeon. Pallids are more often found in areas with sandy stream bottoms while shovelnose also commonly occupy habitats with gravel and cobble substrates.
A more obvious difference between the two species occurs in their food preferences. Starting at a young age, pallid sturgeon eat primarily fish while even large shovelnose sturgeon prefer to dine mostly on aquatic insects. In many species, a diet of fish instead of insects helps them attain a large body size, which pallids definitely have.
Pallid sturgeon can grow to almost six feet long and over 60 pounds while the current Montana state record shovelnose is about 40 inches and 14 pounds. Some scientists think that large body size evolved to help pallids make very long distance spawning migrations in free flowing rivers.
Some information suggests that pallids could have historically moved from as far away as Kansas City, Mo., to Montana spawning areas. These historic migration corridors may have been cut off when parts of the Missouri River were dammed, causing pallids to decline.
Even small dams, like Intake Diversion on the Yellowstone River can have a big effect on movements. Pallid sturgeon were historically found as far upstream as Miles City but have declined in this part of the river over the last 100 years following construction of Intake Dam, which none of our radio-tagged pallids have ever made it past.
Dams appear to have an even bigger effect on the movements of just-hatched sturgeon, as opposed to adults that have been around for tens of years. Immediately after hatching from eggs, larvae of both sturgeons drift downstream but the similarities end there. Shovelnose larvae drift for 4 to 8 days while pallid larvae drift for 8 to 12 days. In the Yellowstone and Missouri riversm this means that larval pallids will drift 200 to 300 miles before they stop moving downstream.
Each spring, the majority of our radio-tagged pallid sturgeon move to possible spawning areas in the lower Yellowstone River less than 50 miles above the headwaters of Sakakawea Reservoir, which means that most larval pallids drift into the reservoir and likely die. A similar situation occurs in the Missouri River above Fort Peck Reservoir.
In comparison, shovelnose sturgeon larvae move shorter distances and, as radio-tagged fish in the Adopt-A-Fish program indicate, adult shovelnose occur much further above reservoirs than pallids during spawning times, which likely results in higher larval survival.
One of the things we'll be watching is how the movements and distributions of the radio-tagged pallids differ from those of shovelnose. The unique adaptations that have allowed pallid sturgeon to thrive for tens of millions of years puts them at risk in today's world while the slightly different adaptations of their close cousins, the shovelnose, allow them to continue to thrive.
Weekly updates on our radio-implanted fish can be found on the Missouri-Yellowstone Adopt-A-Fish home page with updates posted Thursday mornings in April and May. Just click on the Find your Fish button on the home page.
School classrooms, youth fishing clubs and home schoolers can sign up for the program and adopt and name two fish. Just go to the Web site and click on the How To Adopt Button or send us an e-mail at Missouri-Yellowstone Adopt-A-Fish.
Adopt-A-Fish correspondents Dave Fuller, at Fort Peck, and Matt Jaeger, at Glendive, are fisheries biologists with Montana Fish, Wildlife and Parks. They’ll post weekly updates every Thursday throughout April and May on this site and in the Outdoors section of The Billings Gazette.