Alewives rebound in latest Lake Michigan forage fish survey
Written by Green Bay Press-Gazette   
Friday, 11 January 2008 03:58

If there's anything positive that can come out of a survey that found the fewest Lake Michigan forage fish in more than 30 years, it's that alewives are holding their own.

Though at numbers well below the long-term average, alewives — the favored forage for the big lake's multimillion-dollar salmon and trout sport fishery — were up about 18 percent over the fall 2006 survey, which was one of the three lowest ever. 

Chuck Madenjian, a research fishery biologist for the U.S. Geological Survey's Great Lakes Science Center, said scientists believe there were 30 kilotons of prey fish in the lake last fall. That's more than 66 million pounds, but about half of the 2006 estimate.

The biggest drop was in bloater chubs, only at about 1 percent of their high two decades ago. Deep-water sculpin numbers also plunged, and smelt numbers — already very low — declined more.

On the other hand, the volume of quagga and zebra mussels increased about 13 percent, to 245 kilotons. That adds up to more than 500 million pounds of mussels.

"It's almost all quagga mussels now, not many zebras," Madenjian said. "Some trawl catches had over 1,000 pounds of mussels in."

The specially equipped boat — about 75 to 80 feet long, Madenjian said — annually surveys the bottom off seven ports, including Sturgeon Bay and Port Washington off the Wisconsin shoreline. Tows are done every 60 feet of depth, starting in 60 feet of water and ending in 360 feet of water. Ten-minute tows that take only a few minutes to lift at shallower depths can take nearly a half-hour at the greatest depths.

Whitefish and yellow perch will eat the smaller mussels as part of their diet, but it's not enough to stop the growing mussel population from filtering out phytoplankton important to small fish and invertebrates.

"There's a lot of doom and gloom talk these days," Madenjian said. "People are really concerned. But I do think it would be a mistake to put all the blame on the mussels. There maybe were too many salmon in the lake, and bloater populations could be somewhat cyclic. Let's see what happens."

Some commercial fishermen don't think bloater numbers will come back, but Madenjian is not so sure. The population was lower in 1976, he said, prompting an emergency closure.

As for the alewives coveted by salmon and trout — and the anglers who seek them — Madenjian said the most common length seen in the trawls was between 5 and 6 inches, likely from a strong 2005 year class.

Still, alewife numbers were lower only three times since the survey began in 1973.

"The overall trend is smaller size (of salmon)," Madenjian said. "With the states stocking fewer, the numbers might come down some, but it depends on natural reproduction, too."

 
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