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
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
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."