Threat from Grass Carp Highlights Problem with Artificially Connected Great Lakes Basin

In late October, the U.S. Geological Survey confirmed that four grass carp had reproduced in the Sandusky River, in Ohio. This is the first instance of a species of Asian carp reproducing in the Great Lakes basin, and proof that it is more important than ever to keep the more threatening silver and bighead varieties of Asian carp out of the Great Lakes by separating the Lakes from the Mississippi River. Now, a new editorial in the New York Times highlights the importance of separating the Great Lakes for different reasons.

The term Asian carp refers to many species of fish, each with different characteristics. The Asian carp normally referred to as the threat to the Great Lakes are the silver and bighead varieties that eat massive amounts of plankton, and thus have the potential to outcompete native fish throughout the food chain. Grass carp, in contrast, primarily eat water plants and in so doing threaten the ecology of Lakes by changing the rate of plant growth and extent of plant cover. Indeed, because of their specific diet and voracity, grass carp were introduced to the U.S. in 1963, deliberately, to control aquatic vegetation. Further, it was the recommendation of a government task force studying Asian carp that infertile grass carp could be used in lakes and rivers to control aquatic vegetation. As a coalition in Illinois has pointed out, the threats from grass carp to the Great Lakes are different from those presented by silver carp.

The editorial in the New York Times contends that grass carp are a threat in the Great Lakes for another reason altogether: their potential to invade the Hudson River through the Erie Canal. The authors, David Strayer, a senior scientist at the Cary Institute of Ecosystem Studies, and John Waldman, a professor of biology at Queens College, City University of New York, write:

“The establishment of a large population of grass carp, a fish that flourishes in large, turbid rivers like the Hudson, could further endanger this habitat and decimate the river’s already embattled native fishes.”

The Hudson River has a history of invasive species that have traveled from the Great Lakes, and the zebra mussel is a good example. The zebra mussel’s invasion caused an 80 percent decrease in the plankton in parts of the river, which drastically changed the dominant fish species in the ecosystem. Because of the zebra mussel invasion, the aquatic plant life in the Hudson took on an even more critical role in the health of the ecosystem by supplying food for small invertebrates, which in turn, supplied food for fish. Now this critical aquatic vegetation could be significantly harmed by the grass carp.

This concern raised in the editorial is real, but not new. As early as 2005 the Great Lakes Regional Collaboration Strategy recognized the threat to the Great Lakes and other watersheds by keeping them artificially connected. The Great Lakes face the threat of silver and bighead carp invading and successfully reproducing by staying connected to the Mississippi River. A study by the U.S. Army Corps of Engineers, slated to come out in January of 2014, will look at the best options for separating the Lakes from the Mississippi. The Healing Our Waters-Great Lakes Coalition hopes this will provide a blueprint for permanent separation of the two bodies of water. If we do not separate the Lakes from the Mississippi, the threat from invasive species could extend far beyond the Lakes and into the Hudson River.


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