Here is a comparison of prey fish abundance in Lake Michigan in 2006 and 2007. Prey fish are bloaters, alewife and other species eaten by larger fish: salmon, lake trout and whitefish: |
The volume of all prey fish in the lake -- alewife, bloaters and other small fish eaten by salmon, lake trout and whitefish -- dropped by half, from 61 kilotons in 2006 to 30 kilotons in 2007, according to data compiled by the U.S. Geological Survey's Great Lakes Science Center.
That's the lowest volume recorded since the government began tracking prey fish densities in 1973. Prey fish abundance last year was 92 percent below the record volume of 400 kilotons recorded in 1989, said Chuck Madenjian, a USGS research fishery biologist.
At the same time prey fish numbers are plummeting, the volume of foreign dreissenid mussels in Lake Michigan -- quagga and zebra mussels -- increased 13 percent in 2007, according to USGS data. There were 245 kilotons of quagga and zebra mussels in the lakes, eight times the volume of all prey fish; quaggas account for 98 percent of the mussels in the lake, according to government data.
"Most of the stuff we bring up in our bottom trawl now is quagga mussels," Madenjian said. "Their population has just exploded in the lake in the last five years."
The divergent trends of more mussels and fewer prey fish doesn't bode well for the Lake Michigan ecosystem or the sport and commercial fisheries.
Quagga mussels hog the plankton that comprises the base of a food chain that supports most fish species. The dime-sized mussels, which snuck into the Great Lakes in ocean freighters' ballast water, have been linked to the collapse of Lake Huron's salmon fishery.They are shrinking salmon and whitefish in lakes Michigan and Ontario and causing algae blooms that foul beaches and botulism outbreaks that have killed 75,000 fish-eating birds around the Great Lakes over the past decade.
A state biologist said anglers should expect to catch fewer salmon, and smaller salmon, in Lake Michigan in the coming years. There aren't enough prey fish in the lake to support the near-record salmon catches anglers have enjoyed in recent years, said Randy Claramunt, research biologist for the Michigan Department of Natural Resources.
"I think we're going to see reduced salmon catches in the near future," Claramunt said. "This is not a crash of the salmon fishery, it's more like a soft landing."
