Great Lakes fish experts behind moves to hold
off Asian carp
03-12-2009 Dave Spratt / Special to The Detroit News, USA
The Great Lakes do not need this. The Chinook salmon already have been starved out of Lake Huron and they're doing a delicate balancing act in Lake Michigan. The problem is a lack of plankton, the tiny critters that feed the small fish that feed the big fish.
That critical plankton problem comes courtesy of invasive zebra and quagga mussels. Now, we're looking at an invasion of Asian carp -- some of the most ravenous plankton-eaters on the planet. There are fears they already have passed man-made barriers and will eventually cause the collapse of Great Lakes fisheries.
Today, teams from all eight Great Lakes states including Michigan, the federal government and Ontario are poisoning a seven-mile stretch of the Chicago Sanitary and Ship Canal. The five-day process is designed to kill off every fish in there, because there are concerns that Asian carp are perilously close to Lake Michigan, and the electrical barrier that holds them out needs to be shut down for maintenance.
The poison will kill what's there, and then the barrier will be turned back on. Another barrier -- for a total of three -- will come online next year. But the barriers are imperfect. They can't stop fish movement if there's flooding, for example. Some people have questioned their value. Building and maintaining them costs money.
But if enough Asian carp reach the Great Lakes and establish a population, it's not unreasonable to expect some very important players -- salmon, whitefish, lake trout -- to suffer in lakes Michigan and Huron. Walleye are the lifeblood of Lake Erie, both to the American sportfishing industry and the Canadian commercial fishery. They've become the premier sport fish on the U.S. side of Lake Huron, too. It just so happens that in Germany the introduction of Asian carp has most affected the zander, which is essentially the same species as walleye.
"The worst case is exactly what's happening on the Mississippi River, where Asian carp are found en masse," said Jim Dexter, the Lake Michigan Basin Coordinator for the Michigan Department of Natural Resources. "It's a very productive system where there's a lot of food for those fish, and the effects have been devastating. They have displaced virtually all the native species and comprise virtually all the biomass in those stretches."
There's still hope that such a disaster could be averted in the Great Lakes, especially if strong efforts to keep the fish in their place continue. Ironically, the existing food-web problems in lakes Michigan and Huron could ultimately prevent the Asian carp from ever taking hold, Dexter said.
"Our collective opinion is that in Lake Michigan and Lake Huron I do not believe that there's a high probability of huge numbers of these fish being able to survive and do well," he said. "The food resources are just not there. The bottom of the food chain has changed so dramatically in the past few years."
What's more, there is a fairly huge gap between a few Asian carp getting into Lake Michigan and Asian carp taking it over. Duane Chapman, a biologist with the United States Geological Survey (USGS) and a leading authority on Asian carp, acknowledges that carp in the Great Lakes are hardly a good thing: "Once it starts, I don't see an upside." But he also said a lot of things will have to happen in order for the carp to do in the Great Lakes what they've done in the Mississippi.
"Just getting a couple fish past the barrier wouldn't be enough to probably start a population," Chapman said. "If you have a male and female at the same place at same time it's possible, but the chance of that is not very likely. It typically takes multiple introductions for an invasive species to get started."
That's what happened in the Mississippi River. The fish were initially imported in the 1960s to help fish farmers clean their ponds. Their release into the Mississippi is often blamed on widespread flooding in 1993, but Chapman said Asian carp began escaping into the Mississippi shortly after they were brought to the United States. They existed in the river in low numbers from the late 1970s on. Their numbers exploded in the 1990s.
In this undated file photo, the invasive species silver carp, a variety of the Asian carp, is pictured by the Illinois River in central Illinois. AP
"They've gotten to be just totally out of control, but it didn't happen overnight," Chapman said. "The Great Lakes are a huge system. If they get in there, I fully expect them to not immediately take off and have a giant population."
Chapman added that much of the Mississippi River system has maintained a strong fishery for its key species, namely flathead catfish, channel catfish and blue catfish.
One more limiting factor, Chapman said, is the carps' life cycle. To successfully spawn, Asian carp need rivers that flow unimpeded for up to 100 kilometers, or about 60 miles. Many Great Lakes tributaries are dammed; Chapman said only 22 U.S. rivers have been identified as long enough to allow them to spawn successfully. Other factors like flow rates and water temperature could even reduce that number. On the other hand, many Canadian tributaries of Lake Huron have no dams at all, and the USGS doesn't count those.
"If you got enough fish in there, some of them are going to figure out where the right place is, and that's why keeping the number down over time is very important," Chapman said.
A handful of Asian carp have been found in Lake Erie, but those are suspected releases from live fish markets. Unlike the Mississippi, where Asian carp spilled in repeatedly over time, the Chicago Sanitary and Ship Channel appears to be the one place the carp can enter the Great Lakes.
There are barriers there. And poison raining down today. And that's exactly the kind of steady pressure that's needed to keep the carp from the Great Lakes, according to Chapman. It costs between $1 million and $2 million a year to keep those barriers in place. It's money well spent, he said.
"It isn't going to be the end of the world if you can keep the population down," he said. "It does make sense to keep this barrier in place. The game is not over."
Dave Spratt is editor of http://www.greatnorthernoutdoors.net/. He can be reached at dspratt@greatnorthernoutdoors.net.
(Bron: http://www.detnews.com/)
(Bron foto: http://www.theglobeandmail.com/news/technology/science/asian-carp-may-have-breached-great-lakes-barrier/article1371407/)
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