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Researchers studying sex and the pallid sturgeon
In romance, timing is everything. The same is true, it seems, for fish.
For the past several weeks, researchers have waited anxiously for the moment when two mature female pallid sturgeon leave the comfortable water in Cape Bend Chute and bolt upstream to spawn.
The fish are ready, laden with eggs, said Jim Garvey, an associate professor at Southern Illinois University. The repeated rise and fall of the Mississippi River is one signal the time is right, he said, and rising water temperatures will be another signal.
But the big mystery, and the reason researchers are on the Mississippi River around the clock with hydrophones and other monitoring equipment to track the females, is that little is known about where pallid sturgeon like to spawn, how long it takes and what the fry do when they hatch.
"We never seem to be there at the exact time they decide to move," Garvey said. "We darn well are going to be out there when the cue happens and they move, and we will use the fancy fish finder to ascertain whether we have a spawning area."
Pallid sturgeon have been on the federal endangered species list since 1990. The fish is partial to the main channels of big rivers and once was found from the upper Missouri River in Montana to Louisiana. Pallid sturgeon closely resemble their cousins, the shovelnose sturgeon, which have become an increasingly important source of roe used as a replacement for banned beluga caviar.
That creates issues for commercial fishers and wildlife agents. Shovelnose sturgeon may be comercially harvested in many locations, including the Mississippi River as it passes Cape Girardeau. It is a federal crime to take a pallid sturgeon from the river without permits.
Massive changes on the big rivers of the central U.S., the result of a decades-long push for reliable navigation and flood control under the direction of the U.S. Army Corps of Engineers, has deprived the pallid sturgeon of access to slack water and side channels scientists believe it favors for spawning.
As environmental concerns have increased, the corps is devoting more money to habitat restoration; Cape Bend Chute and Marquette Island are two examples of how the corps has altered the way it manages the river to create wildlife habitat within the banks of the river.
Meanwhile, millions of dollars have been spent on the Missouri River to create habitat that scientists hope will be attractive to spawning sturgeon, but no one is really sure what setting the pallid sturgeon seeks for nesting, said Dave Herzog of the Missouri Department of Conservation's Big Rivers and Wetlands Field Station in Jackson. The field station and Southern Illinois University are partners in the research, each supplying field researchers and fisheries scientists and sharing the cost of keeping the boats on the river.
"The reproduction of the pallid sturgeon is one of those holy grails," Herzog said. "We want to know where and when. We have issues with hybridization, with the female pallids and male shovelnose interbreeding, so we want to know how, we want to know where and we also want to know when."
97 and 99
The two females being tracked are known, unromantically, as Nos. 97 and 99. They are equipped with beacon tags that emit a high-pitched ping about once a second. Data embedded in the signal tells the researcher which fish they are hearing. The pair of fish are valuable assets for science because pallid sturgeon must live 15 to 20 years before maturing. They can live up to 50 years.
On Wednesday, after picking up Garvey, research assistant Sara Tripp, two SIU-Carbondale publicists and two Southeast Missourian journalists, SIU research assistant Nick Wahl and conservation department assistant Tyler Stearns steered their vessel from the Red Star boat ramp to Cape Bend Chute where 97 and 99 have spent a lot of time lately.
After using the hydrophone to assure themselves that 97 and 99 hadn't started their upstream swim, the researchers set up an echo finder capable of detecting both the pallid sturgeon and whether they have any company. The echo finder also records water velocity, depth and sediment load.
"We overlay all this, and it gives us an idea of the environment the fish is in," Garvey said as he explained the blue, green and red readouts displayed on a laptop computer.
The researchers are prepared to follow 97 and 99 as far north as the Chain of Rocks above St. Louis and as far south as Cairo, Ill. They have an appropriation of $150,000 from the corps' St. Louis District office to follow the hatched fish after spawning.
One issue that must be resolved, Herzog said, is the relative number of pallid sturgeon compared to shovelnose in the middle Mississippi River. Anecdotal records going back more than 100 years include reports of pale sturgeon being harvested in the river, he said. "We just don't know. Is this truly a rare and endangered fish or is it a low level that is maintained?"
Most of the pallid sturgeon being caught and tagged in the middle Mississippi River are too young to spawn, an indicator that some older fish are present and spawning, Herzog said. But the lack of large numbers of older fish creates concerns that commercial fishers are harvesting pallids for their roe rather than returning them to the river. "We are trying to answer those things, and it is very contentious," he said.
Another question that must be answered, he said, is whether pallid sturgeon return to a home location each time they spawn or if they are opportunistic and use any available site that is suitable.
Once the researchers have found a location where pallid sturgeon spawn, scientists will report the details of their find to the corps, Garvey said. "We will tell the corps it is a special location, tell the corps why it is special and tell the corps to make more of them."
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On the Net
Pallid sturgeon fact sheet: www.mt.nrcs.usda.gov/news/factsheets/pal... Southern Illinois University-Carbondale Fisheries & Illinois Aquatic Center: fisheries.siu.edu/