Common Scents
 | | Dr. Peter Sorensen (left) and Dr. Ron Thresher have been working on a multiyear plan to control carp in U.S. and Australian waters. |
In the darkened basement of Hodson Hall, surrounded by tanks and tubes, a student watches three female goldfish move across the screen of a video monitor. Slowly, she infuses water from a male goldfish's tank into the water in which they're swimming and waits to see their reaction.
The student's observations are the latest of thousands made in the laboratory of Peter Sorensen, professor of fisheries, wildlife and conservation biology. For more than two decades, Sorensen has been studying pheromones-chemicals that convey behavior-altering information from one member of a species to another. His laboratory is one of a few in the world that focuses on pheromones in fish. "Most freshwater fish are like dogs-they get around their environment by sniffing," Sorensen says. "There's a whole world to be discovered, which is not only fascinating but potentially very useful. Many cues are extremely specific and potent, and thus might be added to natural waters to alter fish distributions to the benefit of fisheries managers."
Sorensen began studying pheromones as a graduate student in the 1980s, when he found that the behavior of eels migrating into freshwater streams from the Atlantic Ocean was strongly influenced by extremely low concentrations of various natural odors. Soon afterward he and his colleagues described and identified five goldfish sex pheromones-the first to be clearly elucidated in a fish.
In the past decades Sorensen and his colleagues have learned much about the kinds of compounds that serve as pheromones-how fish make them, how other fish detect them, and how they produce changes in physiology and behavior. Recently, he has focused on the possible application of pheromones to invasive species control. One emphasis has been the sea lamprey, an invasive parasite that represents a formidable threat to Great Lakes fisheries. With funding from Minnesota Sea Grant, the Minnesota Agricultural Experiment Station, and the Great Lakes Fishery Commission, Sorensen and his students and colleagues have isolated and identified a migratory pheromone released by larval lamprey that other lamprey can detect at concentrations of less than 1 ounce in 100 billion gallons of water.
More than a decade of study culminated this summer in a field test demonstrating that the pheromone could be used to lure lampreys into traps in the wild. Biologists with the U.S. Fish and Wildlife Service are now collecting and concentrating water at a Michigan lamprey "farm" to provide pheromones for further trials-and potential application-next year. "We almost have the lamprey thing licked to the point where we can hand it over to fisheries," Sorensen says.
Carp control
More recently Sorensen has been looking at using pheromones to control another nonnative fish, the common carp. This species was introduced into the Midwest in the 1800s as a food source for settlers. It has since become the bane of many Minnesota lakes, muddying the waters and degrading ecosystems with its bottom-grubbing feeding behavior.
Several years ago Bill Oemichen ('49) was frustrated with the devastation, so he provided funds to support preliminary research on using pheromones to control common carp. Sorensen later received a small grant from the Minnesota Department of Natural Resources and the Legislative Commission on Minnesota Resources to continue the work. Last year, after presenting a paper on pheromonal control at a fisheries conference in New Zealand, he was invited to join a multimillion-dollar, seven-year program in Australia to eradicate common carp. That project is exploring many innovative techniques, including genetic control, which Sorensen believes will inform efforts to control carp here as well.
Although carp are harder to work with than goldfish, they are showing much promise as candidates for pheromone-based management. "We've seen evidence they use many of the same types of cues," Sorensen says.
Recently Sorensen has been called upon to add his expertise to an arsenal being gathered for yet another invader coming our way. Known collectively as Asian carp, four closely related species of plankton-eaters are working their way up the Mississippi River toward Minnesota. Natural resources managers fear they will cause significant harm to native fish when they settle in. "People look at this issue and think, 'What the heck are you going to do?'" Sorensen says. One approach he's looking at is to use "alarm" pheromones as repellents to discourage the nonnative fish from moving into new waters. He's now exploring the idea in collaboration with Missouri researchers.
If our experience with other non-natives is any indication, preventing Asian carp from harming Minnesota's waters will be a challenge. But Sorensen is optimistic that science is up to the task-if adequately funded and conducted in an imaginative manner. "If you can cure cancer and you can put a man on the moon, you can certainly deal with these species," he says. "Can something be done for carp in Minnesota? The best example is the sea lamprey, and the answer is yeah, and it's being done."
Written by Mary Hoff
Photo from the Minnesota Agricultural Experiment Station
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