Friday, June 26, 2015

Locking out Asian Carp at St. Anthony Falls

Water & Watersheds

by John Shepard

When they're agitated, high-flying Asian carp as big as porkers can conk people on the head and knock them out of boats. Two weeks ago, these noxious aquatic invaders gave the upper Mississippi River shipping industry a whack on the side of its noggin—a singular occurrence at a place of extraordinary convergence: St. Anthony Falls in downtown Minneapolis.

Stone Arch Bridge and downtown Minneapolis (Creative Commons)

St. Anthony Falls

At the Falls, elements from the past—ruins of historic flour mills and a magnificent stone-arch railroad bridge that is now a half-mile long park—are surrounded by glimmering new buildings. Coal and hydro power plants provide background for art festivals, outdoor operas, and place-based performance dance events like CGEE's longstanding Solstice River. Recreational paddlers, joggers, strollers, bikers, and two-wheeled electric Segway riders segue with commercial traffic on land and water. And on June 10, 2015 nature crashed into hubris, or maybe just shortsightedness.

The Invasive Threat

Four of the seven species of Asian carp brought to the U.S. in the 1970s to control weeds and parasites in fish farms—bighead, black, grass, and silver—have become a major menace. Since escaping into the wider world, they have been making their way upstream through America's river systems, over-eating and out-competing native fish along the way. Unlike the relatively benign common carp, which have been in the U.S. for more than 100 years without stirring up too much trouble, the Asian carp reproduce with abandon, can consume up to forty percent of their body weight each day, and can fatten up to more than 100 pounds. They tend to completely dominate aquatic ecosystems wherever they get established. 

Vibrations from outboard motors drive the fish into a frenzy and they leap high into the air in spectacles that have inspired a new kind of sport—assaulting the flying carp with arrows, swords, and spears. 

Keeping the carp out of the Great Lakes has become a driving priority for wildlife managers, but even if that effort succeeds Asian carp are poised to "spell disaster for our nation's freshwater ecosystems," according to the National Park Service. The Service estimates that freshwater fisheries could be impacted in as many as 31 states. At a recent public meeting, Chris Stein, superintendent of the St. Croix National Scenic Waterway, warned that the impact of these invasive fish on that pristine Mississippi River tributary would make other threats, like expanding development, pale in comparison.

Shutting down the Lock

Regression of the falls from 1680-1887
(U.S. Army Corps of Engineers)
In an attempt to keep the carp from traveling any further upstream, on June 10 officials closed the massive steel doors of the river's two uppermost locks—maybe forever. Since 1963 the locks have allowed passage for barges and recreational craft around the river's only major waterfall, which was encased in concrete to prevent its continual and rapid erosion (10,000 years ago the falls were several miles downstream where Ft. Snelling is now). 

I will miss "locking through" these giant passageways in a puny canoe or kayak. Doing so involved hanging onto a rope as 10 million gallons of water released from the lock chamber into the murky downstream currents enabled a 50-foot descent that took only a couple of minutes. Then giant doors would slowly open to views of the historic bridge and the river below (the video below of canoes passing through Lock and Dam # 1 a few miles downsteam of St. Anthony Falls was made during a CGEE Mississippi River Institute in 2010).

Back to the Future

For paddlers, the past will intrude into the future once again, as the ancient portage around the falls will become the only way for vessels to beat the carp in the quest to reach upstream waters.  

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