Great Lakes food web devastated
Written by The Pilot-Independent   
Thursday, 30 December 2004 10:13
It's often said that the devil is in the details.

A new report by the National Wildlife Federation (NWF) on the toll of invasive species to the Great Lakes food web, a phenomenon that's impacting some of our most storied sport fisheries more every day, is a case in point. Problem is, it is as if the devil has been cloned a dozen times over.
The 44-page report, the most exhaustive I've seen on the subject, provides an in-depth look at the devastating effects that invasive species are having on the multi-dimensional food chain of the Great Lakes.
As the foreword of the report states, non-native species are "harming fish at the top of the food web and decimating organisms at its base."
As a result, the ecology of the lakes (Superior, Michigan, Huron, Erie and Ontario) is changing at an alarming rate, the repercussions of which are being felt by everyone, including sport anglers.
"What we're trying to do is raise the issue of invasive species so that action is taken," said Mike Murray, NWF staff scientist for the group's Great Lakes office. "We're trying to generate broader public and private interest about the issue. The stakes are very high."
The Great Lakes are enormous bodies of water and widely hailed as national treasures. In raw numbers, they make up about 20 percent of the world's surface freshwater, enough to fill the Grand Canyon and submerge the continental United States under nine feet of water, according to the report.
The Great Lakes are also economic hubs, affecting eight states and two Canadian provinces. The lake's sport fisheries alone support 75,000 jobs, with an additional 9,000 linked to commercial fishing. Another statistic from the report: Recreation and tourism in the region is "valued at $15 billion annually with $6.98 billion related to the fishing industry."
"Invasive species are not a regional problem," said Murray, who coordinated the project. "They've slowly worked their way south and west of the Great Lakes for the last decade. It is in everyone's best interest to fix this problem."
As I've detailed in this space in other columns, the invasive species found in the Great Lakes represent a wide range of organisms, including aquatic plants, invertebrates, fish and algae. Since the 1880s, at least 160 exotic species have invaded the Great Lakes, researcher say, many of which hitch rides on U.S.-bound ships and are introduced through ballast water discharges, however unwittingly.
Let's concentrate on one piece of this complicated puzzle.
According to Murray, a key part of the Great Lakes food web is macroinvertebrates (small animals without backbones) that "link algae with fish communities." Aside from fingernail clams and other native organisms, diporeia ? a tiny shrimp-like amphipod ? is of biggest concern to researchers.
Diporeia, Murray said, are an important, high-energy food source for many fish. "Most fish feed on them [diporeia] at some point in their life cycles," he said. "They're very important to the food web."
But diporeia, along with fingernail clams, have declined significantly over the last 20 years, in large part, researchers believe, due to the introduction of two invasive species: zebra and quagga mussels.
The upshot is that scientists, Murray said, have observed "impacts" on fish that depend on diporeia as a food source.
For example, in Lake Erie, smelt populations have declined. In Lake Ontario, slimy sculpin and young lake trout have declined. In Lake Michigan, whitefish have shifted from eating diporeia to the more abundant but less nutritious zebra mussel, the result of which is leaner and smaller whitefish, according to the report. The same chain of events is true for the decline of fingernail clams. Poor recruitment (reproduction) of yellow perch since the 1980s is also thought to be tied to the decline of diporeia.
Because yellow perch are forage for walleyes, muskies, northern pike and other sport fish, their decline can impact a number of fisheries.
"It's a complicated puzzle to explain, let alone understand," said Murray. "That's one of the many challenges we face."
The NWF, along with a laundry list of local, state and federal agencies such as Sea Grant, say a multi-pronged approach is needed to mitigate the problem of invasive species and their ecosystem-wide impacts.
Targeted and better-funded public policy initiatives are a start; many are pending right now in Congress. Critical "knowledge gaps" cry out for more research. Public education must continue ? and even increase.
It is my hope that the NWF report inspires lawmakers, researchers, industry leaders and average citizens to work together to protect the Great Lakes from the ominous and costly presence of invasive species.
The time to act is now.

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