Usually, Asian carp only make the news when an airborne lunker knocks a boater out cold. While the danger of injury from the frequently-leaping 50-pound fish is nothing to laugh at, the real danger is the huge ecological threat posed by these non-native species once they reach the Great Lakes. They have already turned large stretches of the Mississippi River into carp zones, where they make up over 95% of the fish species. That’s why I was glad to see the Detroit Free Press feature an article on the carp on the front page of their Sunday edition, and I hope plenty of people will sit up and take notice when they read,
If the carp do reach the Great Lakes, most experts warn that the lakes will become giant carp ponds where other species, such as salmon, lake trout and walleyes, are starved out of existence. After colonizing the lakes, experts say, the carp would assault rivers and their tributaries.
Unless Congress can get off its duff and authorize funding for an electronic barrier across the Chicago Sanitary and Ship Canal to supplement the current, poorly functioning one, the entry of the carp into Lake Michigan — if it has not already occurred — will be a foregone conclusion. The carp have been spotted less than 50 miles from the lake.
The two species of Asian carp that are posing this threat are the silver carp (Hypophthalmichthys molotrix) and bighead carp (H. nobilis), natives of southeast Asia that were introduced into Arkansas aquaculture farms for algae control in the 1970s. Floods, levee breeches, and perhaps intentional release allowed them to escape into the Mississippi River system. They are now found as far north as Minnesota, and south to Louisiana, altering ecosystems and sometimes wiping out fisheries along the way.
One adult Asian carp can eat 40 pounds of zooplankton and phytoplankton a day. Multiply that by millions of carp (each female can produce 2 million eggs), and you have an situation that quickly and dramatically undermines the base of the food chain. It’s not hard to imagine the disastrous consequences to the vast array of invertebrates, fish, and other aquatic organisms that rely on this plankton for survival. And this impact will eventually be realized farther up the food chain, when the gulls, terns, grebes, loons, and other birds that feed on small fish find their food sources depleted.
Lest you doubt the impact a filter-feeding organism can have on a large lake ecosystem, let’s look at the zebra mussel, another aquatic invader introduced into the Great Lakes via ballast water in 1988. They are also very efficient filter feeders. They are presumed to be the cause of the dramatic rapid decline in diporeia (“scud”), small crustaceans that are one of the cornerstones of the aquatic food chain. Both the diporeia and mussels compete for the same microscopic food. The diproreia decline (click graphic for Lake Michigan history) is now impacting Great Lakes aquatic communities.
Zebra mussels have also indirectly caused tens of thousands of bird deaths in Lake Erie due to botulism poisoning. The mussels are so effective at filtering the water that clarity greatly increases. Increased sunlight leads to more algae growth. When algae blooms die, the decomposition consumes oxygen. Botulism bacteria thrive in anaerobic conditions. Mussels concentrate the bacteria and are eaten by gobies (a non-native fish) . Birds — many loons, grebes, gulls, and other waterfowl that eat mussels or gobies usually die.
The zebra mussels that filtered the lakes and began these chain reactions are the size of a thumbnail. Asian carp have been called “100 pound zebra mussels.”
I follows that diminished fish forage has an impact on the health and reproductive success of colonial waterbirds in the Great Lakes, although I am not aware of any published studies. I suspect that eventually migratory songbirds that follow Great Lakes shorelines and rely on aquatic insect larvae hatches during spring migration may also be effected by these profound ecosystem alterations.
We have few weapons against Asian carp once they are established. They don’t take bait, and avoid nets. We have to try to prevent them from entering Lake Michigan. An electronic barrier was installed in the Chicago Sanitary and Ship Canal in 2002, but it does not span the entire canal, is deteriorating, and was only intended as a stop-gap project. A new barrier was started in 2004, but has not been completed due to lack of funding. The Free Press article reports,
A faltering, temporary electric barrier outside Chicago, in theory, keeps the Asian carp from entering Lake Michigan. A more powerful barrier, with two rows of electrodes crossing a canal, should have been in place last October, but Congress has yet to approve $16 million in funding.
This barrier, which will also help prevent the spread of other exotic species into the Great Lakes, may be our only defense, although fish may be able to pass through the barrier in the wakes of large ships. And it does nothing to prevent ballast dumping or other means of introduction into the Great Lakes.
Please consider writing to Congress to speed up authorization for funding of the barrier. Great Lakes state Congress members are in favor of the funding, so it is especially helpful for people living away from the Great Lakes to encourage their representatives to sign on. You can look at sample letters (PDF) by the Great Lakes Fishery Commission to House and Senate members; for the mailing or email address of your own House members, go to this site, and this one for your Senators. While you are at it, encourage them to support reauthorization, strengthening, and funding of the National Aquatic Invasive Species Act, legislation that is critical to preventing and understanding invasive species in the U.S. and which has also suffered from non-action.
- Scientists Fear Leaping Carp to Invade US Great Lakes
- Leaping carp video from Minnesota Public Radio
- Invasive Asian Carps in North America 2006 Symposium — abstracts online
- Wisconsin Sea Grant invasive species pages have a great deal of info on barrier issues
Flying carp: USGS
Diporeia graphic: Milwaukee Journal Sentinel