Lampreys make a surprise showing
Written by Detroit Free Press   
Friday, 01 September 2006 04:50

Many anglers who fish the St. Clair River and Lake St. Clair have been surprised this summer to find small lampreys clinging to muskellunge, catfish, pike, walleyes and even smallmouth bass.

State and federal biologists say that lamprey numbers in those waters do appear to be up, but they probably don't present a threat to game fish because they are small, native silver lampreys, not the larger and more voracious exotic sea lampreys that nearly wiped out the Great Lakes lake trout populations 50 years ago.

Walt Thomas of Port Huron said he began finding lampreys on walleyes earlier this summer. "For a while there it seemed like half of the fish had lampreys on them. They weren't very big, but there sure seems to be a lot of them," he said.

"My buddy fishes for muskies on (Lake) St. Clair and said he caught fish with four, five of these things on them. We can't figure out what's going on. I thought they were supposed to have spent millions of dollars trying to reduce lampreys."

Gary Towns, the Michigan Department of Natural Resources fisheries resources manager for southeastern Michigan, said, "We've seen larger numbers (of lampreys) in those areas, but we're not sure why. They're probably all silver lampreys, although some of them can be very dark in color."

Michigan has four native lamprey species: northern brook, brook, silver and chestnut. They all spend several years as worm-like ammocetes in the bottom mud, then transform into eel-like adults that live eight to 20 months.

The brook lamprey species are not parasitic. In fact, they stop feeding after transforming to adults and die in a few months. Silver and chestnut lampreys do become parasites as adults, using their round sucker mouths filled with hooked teeth and a file-like tongue to bore into soft-scaled fish and suck their body fluids.

Chestnut lampreys are more common in streams on the Lake Michigan drainage, where they commonly parasitize trout, while silver lampreys are found more often on the eastern side of Michigan.

But silver and chestnut lampreys are small. They average about 10 inches and look like big nightcrawlers, and unlike sea lamprey, which grow to two feet, they rarely kill their hosts.

"It doesn't make much sense to kill your host species, because eventually you'll eat yourself out of house and home and you'll die, too," said Dennis Lavis, who runs the U.S. Geological Survey's lamprey research facility at the Hammond Bay Biological Station on Lake Huron.

Towns said, "It might be that the increased cleanliness of the water has increased the survival of the juvenile lampreys," referring to greatly reduced toxin levels in the Great Lakes and associated rivers in recent years.

Lampreys, both native species and sea lampreys, are even more sensitive to polluting chemicals than most native game fish, and the effort to reduce pollution in most Michigan rivers has given all species of lampreys more places to spawn.

"The juveniles live in U-shaped burrows in the sediments for several years and feed on detritus," material that drops to the bottom and decomposes, Towns said. "It could be that the bottom sediments have just got so much cleaner that more of the juveniles are surviving to adulthood."

Lavis said the difference between native lampreys and sea lampreys illustrates the havoc that can be caused when a new species is introduced to an established ecosystem.

"The silver and chestnut lampreys evolved with the other animals in the Great Lakes. They've had thousands of years to figure out how to get along," he said. But sea lampreys evolved in the oceans with access to much larger prey. When they came into the Great Lakes through man-made shipping canals, they preyed primarily on slow-moving, soft-skinned lake trout, which were the biggest fish available that the lampreys could easily parasitize.

Within about 30 years, lake trout were virtually wiped out in most of the Great Lakes, because unlike native lampreys, the bigger sea lampreys drained the fish until they died.

"Silver lampreys don't usually kill fish," Towns said. "They feed on them for a while and then drop off. I'm sure some smaller fish do die from the (parasitism), and if you had 20 on a big fish like a muskie it would probably kill it, but that's not they way they work.

"There probably were a lot more silver lamprey in the pre-settlement days" before the rivers were polluted, Towns said. "But who knows? We may be seeing a resurgence, or maybe we're seeing the peak of a cycle. These (waters) are changing so fast, and we've got a lot to learn."

 

 
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