Tracking Asian Carp in the Mississippi
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By Tom Eisenhart
Nothing ruins a day of fishing or jet skiing on the Mississippi faster than being slapped upside the head by an Asian carp. Even worse than that is getting knocked unconscious by one of the leaping fish.
It may be hard to believe, but the risk of getting KO'ed by an Asian carp on the Mississippi or one of its tributaries is a growing threat, according to John Chick, a field director and aquatic ecologist with the Illinois Natural History Survey and The National Great Rivers Research and Education Center. The culprits are silver carp, one of two species collectively known as Asian carp, which leap out of the water when they become startled by passing boats.
Today our crew meets up with John on the banks of the Illinois River near Grafton, Illinois. We're here to learn about bighead and silver carp, Asian carp species that have invaded the Mississippi River system and whose numbers and range continue to grow.
Unfortunately (or perhaps fortunately, considering the risks) a scheduling conflict will keep me from joining John on the river to see the jumping phenomenon first hand. But Andrew Simpson, one of our crew's videographers, and Mark Godfrey, our photographer on this leg of the trip, will join John and his crew to see if they can 'rustle up' some Asian carp for our cameras.
John knows more than a thing or two about Asian carp. He co-authored a number of papers examining their impact on native species and ways to potentially control their spread.
Asian carp are filter-feeding species, which means they vacuum up zooplankton, algae and other small aquatic organisms, much like native paddlefish and bigmouth buffalo do.
Because of their voracious eating habits, they were introduced to the United States as a way to cleanse catfish ponds in southern states. During floods sometime in the mid- to late 1980s, Asian carp escaped into the Mississippi River and its tributaries and found the new waters to their liking.
Having read about how rapidly Asian carp can grow — they can reach three to four feet in length and weigh more than 100 pounds — I assumed they must be an ecological disaster for the Mississippi and tributaries where they've gained a 'finhold.'
Research to date hasn't provided a conclusive answer. Last year, John and his science colleagues published their findings on the diet overlap among Asian carp and three species native to the Mississippi and Illinois rivers. Their research showed that of the three native species studied — paddlefish, gizzard shad and bigmouth buffalo — the diet of Asian carp and gizzard shad overlapped significantly, less so for the other two native species.
Yet even in the case of gizzard shad, ongoing monitoring has not indicated a decline in their numbers because of Asian carp. As John explains, the reason that Asian carp have not eaten native filter-feeding species out of house and home is because plankton, their common food source, is extremely abundant in the Mississippi and Illinois rivers.
There is some evidence from the Illinois River that the condition of gizzard shad and bigmouth buffalo has declined in recent years — individuals from these species are becoming thinner. Yet scientists have not documented population crashes.
While the jury is still out on exactly what impact Asian carp are having on the river's ecology, "state and federal agencies agree this is an invasive species that no one wants here," says John.
Controlling Asian carp numbers, however, is no easy task. There is some commercial harvesting of Asian carp on the Mississippi and Illinois rivers. But markets tend to be limited; Americans generally aren't fond of the idea of eating carp, which is compounded by the fact that Asian carp filets are very bony. Bio-controls could be an answer, but it's challenging to find a solution that will control carp without harming native species.
One potential solution may come from the increasing number of hybrid Asian carp in the river. Scientists are finding that bighead and silver carp are mating with each other. The hybridized fish, in turn, mate with other bighead or silver carp.
"Typically, hybrids don't do as well reproductively in the long run as pure strains of a species," John explains. Taking that one step further, it may be possible to further curtail reproduction by introducing sterile Asian carp.
When we all get back to our hotel later in the afternoon, I find out that maybe it wasn't such a bad thing to miss my close encounter with leaping carp. Andrew and Mark look a bit glum; dried white slime and scales cover their clothes and equipment. At least they weren't knocked out cold.September 26, 2013