Evolution rapid in Great Lakes fishing
Written by The Ithaca Journal   
Tuesday, 16 May 2006 16:02

Changes in the biology of the Great Lakes once crept along at the snail's pace of evolution. Today, nervous scientists see radical changes occurring in years rather than centuries.

For example, salmon fishing in Lake Huron collapsed within two years of the disappearance of alewives, their primary prey fish.
 
Some researchers, however, think it's a temporary problem. They think Huron's prey base can be repopulated by alewives produced in the vast, rich nursery grounds of southern Lake Michigan.

Mike Gnatkowski, a charter captain in Ludington, Mich., hopes the optimistic scientists are right.
“We had great salmon fishing last summer, about as good for numbers as you could want,” said Gnatkowski. “But they definitely were smaller than we saw two or three years ago.”

Southern Lake Michigan is warmer and richer than southern Lake Huron. The bottom end of Lake Michigan is more than 100 miles farther south than the bottom end of Lake Huron. It also covers a much bigger area and is more influenced by weather systems that come from the Gulf of Mexico.

Southern Lake Michigan is fed by numerous rivers, and currents and upwelling stir the nutrient-laden water into a nourishing broth. This supports a huge population of tiny creatures that provide food for bigger animals, including alewives.

In many ways, southern Lake Michigan mimics Lake Erie, the richest of the Great Lakes, in its ability to support life.

When scientists recently sampled 50 miles offshore in Lake Michigan, they found more than 6,000 young-of-the-year alewives per acre, said Randy Claramunt, a biologist at the Michigan Department of Natural Resources research laboratory at Charlevoix.

By contrast, scientists working on Lake Huron last summer found few or no alewives in their nets after hours of trawling. Some researchers suggest the decline is an indication that zebra and quagga mussels have changed the food chain so much that Lake Huron no longer can support large numbers of juvenile alewives.

John Newman, a Flint, Mich., angler who fished on Lake Huron for 22 years, switched to Lake Michigan last summer “because there just weren't enough chinooks left in Huron to make it worth the effort and gas,” he said. “You could fish all day and catch a bunch of lake trout, but you'd be lucky to get one salmon.”

Newman fished out of Grand Haven and Ludington in Michigan in July and August.

“We caught more chinooks than I have in 22 years of fishing for them,” he said. “The only thing that bothered me was their size. We'd get four-year-olds that only went 10 pounds when they should be 16. I'm a little nervous about it because they were starting to look like the Lake Huron fish did before the crash.”

Lake Michigan produced record numbers of salmon last year, but the fish were two to three pounds smaller on average than a decade ago, a sign of poorer nutrition.

Salmon are open-water roamers. They're also short-lived; they don't have time to learn what's best to eat. They spend a few months in the rivers where they hatch and have about three years in the lakes to build mass and reproductive organs for their sole spawning run. Their choice of food is genetically programmed.

“Salmon are wired to eat alewives,” Claramunt said. “They will continue to hunt down the last alewife before they switch to other prey species.”

The salmon have proved so effective in Lake Huron that alewives have virtually disappeared. That was followed by a crash in the salmon population.

Lake Huron's salmon population likely will continue to fluctuate, Claramunt said, “but within a narrower range. Some years salmon numbers will be up, some years they will be down. Fisheries managers need to teach anglers that we can't get away from some fluctuation.”

 
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