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Muskellunge Die-Off in Southeast Michigan Being Monitored

April 25, 2006

A significant number of muskellunge, the second largest game fish in Michigan, have been observed dead over the last month in Lake St. Clair and the St. Clair and Detroit rivers, according to Department of Natural Resources fisheries biologists. The die-off is being monitored by the DNR and volunteer groups in the area.

"Any time a significant number of fish die, we are concerned for the resource and monitor the situation closely to determine the factors behind it," said Gary Towns, DNR Lake Erie Management Unit supervisor. "We feel the current situation has likely been caused by a combination of factors which have impacted the muskies in the area."

Towns said the DNR has essentially ruled out pollution as a factor. He said species such as walleyes, emerald shiners and other minnows, which are more sensitive to pollution, do not seem to have been affected. Anglers are currently catching lots of walleye, bass and other species which appear to be very healthy, Towns added.

DNR fisheries officials feel the die-off of muskellunge could have been caused by several factors including a combination of spawning stress, a warmer winter which may have set the stage for a higher incidence of disease, and recent rapid warming of water over the past several weeks. It is unknown if the bacterial disease first detected in Lake St. Clair muskellunge in 2002, known as musky pox (Piscirickettsia sp.), is involved. Fish with visible signs of musky pox have red rashes and sunken eyes.

Towns said the muskies that are being found in Lake St. Clair and the Detroit River appear to have died about a month ago and were likely on the bottom of the lake and river system. As they have been decomposing, they have floated to the surface of the water, he said. Due to the decomposition, DNR pathologists cannot test the fish for musky pox or other diseases. Only live fish or fish that have been dead for less than a few hours can be tested for bacterial or viral diseases, Towns said.

The rapid warming of the water in the St. Clair River and Lake St. Clair area could be a major factor, Towns said. Normally in late April, the water temperatures are in the mid-40s. Towns said that presently the water temperatures are in the low to mid-50s, and some anglers have reported water temperatures in isolated bays in the 60 degree range. Rapid water temperature changes can put a lot of stress on fish, he said.

In terms of musky pox, Towns said while many muskies may be infected with it, the disease is usually only fatal to a few fish. Musky pox could cause the death of some fish when the fish are under stress, for example during the spring when water temperatures can warm rapidly.

The DNR has contacted Canadian fisheries officials to monitor their side of Lake St. Clair and the St. Clair River as well, and they have reported some dead muskellunge, too. While a musky die-off was observed in the spring of 2003, very few dead muskies were reported in 2004 and 2005.

"We want area anglers to know that we are aware of the problem and we appreciate their reports of dead muskies in the waters of the St. Clair River, the Detroit River and Lake St. Clair," Towns said. "We are actively monitoring the situation to determine the extent of the die-off, however; we feel at this time it is a combination of weather, spawning stress and perhaps some disease factors which have affected the fish."


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