Asian carp, coming to a lake near you?

William D. Balgord

Several members of an invasive fish family are knocking at the door of the Great Lakes. Aggressive immigrant species, otherwise known as Asian carp (originating in China, Russia and Southeast Asia), the “bighead”, “silver”, “black” and “grass” carp, have been found in the upper Illinois River as close as 25 miles from Lake Michigan. Only one remaining lock and dam stands in the way of their grand entry. The interconnecting Chicago Sanitary and Ship Canal (CSSC ) leads directly from the upper Illinois River into Lake Michigan and waters beyond. Once breeding populations establish themselves, they will become a permanent fixture and nearly impossible to eradicate from the Great Lakes.

Bighead and silver carp, voracious filter feeders in their own right, compete with native species like mussels, forage fish, and infant game fish (walleye, trout, and salmon). Invasive Asian carp escaped into the Mississippi River system when fish-rearing ponds in the South, where they were introduced to clarify water, flooded in the 1990s. They have since spread into the Ohio, Missouri, Illinois and Wisconsin River systems and are detected as far north as the Minnesota-Wisconsin portions of the Mississippi up to the mouth of the St. Croix River.

The super-filter feeders grow as large as 100 pounds. An individual may consume daily 25 percent or more of its body weight of plankton (floating algae, insect larvae and tiny crustaceans related to shrimp). Plankton serves as the basis of the food chain that ultimately supports large sport fish. The somewhat smaller silver carp will often jump high into the air above the water surface when disturbed by a passing motor boat. They have caused serious injuries in collisions with unsuspecting boaters and water skiers.

Bighead and silver carp ignore offerings of minnows, insects and artificial baits by angles. They are difficult to catch by hook and line. Their juveniles are easily mistaken for bait fish (gizzard shad) and may be spread inadvertently to new water by unaware anglers. Moving Asian carp is now illegal in all states. Black carp eat mussels, snails and other mollusks and present additional threats to Great Lakes ecosystems. Grass carp are vegetarians that will consume enormous quantities of native aquatic plants before turning to targeted invasive plants like the European milfoil. Using sterile grass carp to control invasive plants has turned out to be a questionable practice at best.

Great Lakes states conservation departments definitely have their work cut out for them. In an attempt to prevent carp from expanding their ranges into Lake Michigan, the attorneys general of several states (Minnesota, Wisconsin, Michigan, Indiana, Ohio and Pennsylvania) joined in suing the U.S. Army Corps of Engineers to close off the CSSC until effective means of eradicating Asian carp from the upper Illinois River are demonstrated. So far federal courts have refused to issue an injunction ordering a permanent closure of the canal.

The State of Illinois joined as a co-defendant arguing that permanent closure would result in a billion and a half dollars in economic losses to Chicago area businesses that rely on shipments through the canal.

The plaintiffs project losses exceeding seven billion annually from impaired sport and commercial fishing and other popular recreational uses in the Great Lakes (including its tributary and distributary river systems throughout the United States and Canada) should the carp be permitted to spread. The case is expected to be heard by the U.S. Supreme Court. Whether the issue is resolved in time is not clear.

The affected states are preparing reaction plans, in the event of further invasions, that may slow and eventually deter these unwanted fish. Whether their efforts can be as successful as the controls on the lamprey eel that focus on electrocuting adult eels as they migrate up Great Lakes tributaries to spawn, remains to be seen. The invasive lampreys that threatened extinction of salmon, whiting, lake trout and steel-head from the Great Lakes in the 1970s have been successfully brought under control (but not exterminated) so that the cold-water fishery could recover. It thrives today, but nervously awaits arrival of the carp.

William D. Balgord, consultant and writer, heads Environmental & Resources Technology, Inc. in Middleton, Wis.