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Biologists concerned about muskie deaths
By Bill Parker
Editor
Mount Clemens, Mich. — The mysterious deaths of hundreds of muskies on the Detroit River and Lake St. Clair has DNR biologists concerned and baffled.
Boaters and anglers started seeing dead muskies floating in the Detroit River just after ice-out on Lake St. Clair, fisheries biologist Mike Thomas told Michigan Outdoor News from his office at the DNR’s Mount Clemens Fish Research Station.
“I first saw some reports on fishing web sites, then we started getting phone calls from fishermen who were seeing two or three dead fish a day over the course of a fishing trip on the river,” Thomas said. “Most of them seemed to be mature, adult fish over 36 inches in size. Most of them appeared to have been dead for a long period of time.”
Thomas said it’s not unusual to see a few dead fish in the spring, especially after a rough winter. But as the reports continued to stack up, so did the concern.
“As the reports continued, it looked like something out of the ordinary,” Thomas said. “We don’t know for sure how many fish there were, but off the cuff, I’d say probably something like 10 fish a day for 50 or 60 days. That’s based on how fast the water runs through the river and from reports from reliable guides and fishermen who are on the river all the time.”
Since all of the fish Thomas recovered were already badly decayed, he believes they probably died in Lake St. Clair and were washed into the river. He also said that because of the bad condition of the fish, the cause of death could not be determined.
However, on opening weekend of muskie season, June 7-8, a fisherman found a dead muskie in Lake St. Clair that was still relatively fresh and turned it over to Thomas. The fish is on ice and headed to Michigan State University for testing.
While Thomas admits he doesn’t know what caused the deaths of the fish, one theory that bears investigating is that the fish were stricken with the Piscirickettsia bacteria.
In May of last year, several muskies were caught in Anchor Bay that had red rashes or lesions on their skin. Testing at MSU by Dr. Mohamed Faisal determined that the fish were stricken with the bacteria.
According to the DNR web site, Piscirickettsia are not known to infect humans or other terrestrial animals. Piscirickettsia has been found to infect a wide range of salmonid fish species causing infection and high mortalities in Chile, Norway, Ireland, and Canada. But until last year’s discovery on Lake St. Clair, it had never been found in non-salmonid fish species.
Similar agents, known as Piscirickettsia-like organisms, have been found to be associated with increased mortality rates in other fish species, including white seabass, black seabass, tilapia, blue-eyed plecostomus, and dragonet. Three of these Piscirickettsia-like organisms have already been reported in non-salmonid fish species in North America.
“Unfortunately we’re not at the point where we can collect any tissue samples from dead fish because the (Piscirickettsia) bacteria dies when the fish dies,” Thomas explained. “Through external investigation there were no lesions on the (dead) fish we found this year like the ones that we found on the live fish that have tested positive. We can’t say for sure if the bacteria had any affect on these (dead) fish.”
Thomas said Piscirickettsia is still present in Lake St. Clair.
“We are still processing fish at MSU, and fish with lesions have tested positive, so it is still present,” he said. “It didn’t go away over the winter.”
A study in the late 1970s indicated that Lake St. Clair had a population of approximately 17,000 adult muskies, based on catch rates and size limits. Thomas estimates that today there are “conservatively” between 20,000 and 30,000 adult muskies in the 420-square-mile lake.
By Bill Parker
Editor
Mount Clemens, Mich. — The mysterious deaths of hundreds of muskies on the Detroit River and Lake St. Clair has DNR biologists concerned and baffled.
Boaters and anglers started seeing dead muskies floating in the Detroit River just after ice-out on Lake St. Clair, fisheries biologist Mike Thomas told Michigan Outdoor News from his office at the DNR’s Mount Clemens Fish Research Station.
“I first saw some reports on fishing web sites, then we started getting phone calls from fishermen who were seeing two or three dead fish a day over the course of a fishing trip on the river,” Thomas said. “Most of them seemed to be mature, adult fish over 36 inches in size. Most of them appeared to have been dead for a long period of time.”
Thomas said it’s not unusual to see a few dead fish in the spring, especially after a rough winter. But as the reports continued to stack up, so did the concern.
“As the reports continued, it looked like something out of the ordinary,” Thomas said. “We don’t know for sure how many fish there were, but off the cuff, I’d say probably something like 10 fish a day for 50 or 60 days. That’s based on how fast the water runs through the river and from reports from reliable guides and fishermen who are on the river all the time.”
Since all of the fish Thomas recovered were already badly decayed, he believes they probably died in Lake St. Clair and were washed into the river. He also said that because of the bad condition of the fish, the cause of death could not be determined.
However, on opening weekend of muskie season, June 7-8, a fisherman found a dead muskie in Lake St. Clair that was still relatively fresh and turned it over to Thomas. The fish is on ice and headed to Michigan State University for testing.
While Thomas admits he doesn’t know what caused the deaths of the fish, one theory that bears investigating is that the fish were stricken with the Piscirickettsia bacteria.
In May of last year, several muskies were caught in Anchor Bay that had red rashes or lesions on their skin. Testing at MSU by Dr. Mohamed Faisal determined that the fish were stricken with the bacteria.
According to the DNR web site, Piscirickettsia are not known to infect humans or other terrestrial animals. Piscirickettsia has been found to infect a wide range of salmonid fish species causing infection and high mortalities in Chile, Norway, Ireland, and Canada. But until last year’s discovery on Lake St. Clair, it had never been found in non-salmonid fish species.
Similar agents, known as Piscirickettsia-like organisms, have been found to be associated with increased mortality rates in other fish species, including white seabass, black seabass, tilapia, blue-eyed plecostomus, and dragonet. Three of these Piscirickettsia-like organisms have already been reported in non-salmonid fish species in North America.
“Unfortunately we’re not at the point where we can collect any tissue samples from dead fish because the (Piscirickettsia) bacteria dies when the fish dies,” Thomas explained. “Through external investigation there were no lesions on the (dead) fish we found this year like the ones that we found on the live fish that have tested positive. We can’t say for sure if the bacteria had any affect on these (dead) fish.”
Thomas said Piscirickettsia is still present in Lake St. Clair.
“We are still processing fish at MSU, and fish with lesions have tested positive, so it is still present,” he said. “It didn’t go away over the winter.”
A study in the late 1970s indicated that Lake St. Clair had a population of approximately 17,000 adult muskies, based on catch rates and size limits. Thomas estimates that today there are “conservatively” between 20,000 and 30,000 adult muskies in the 420-square-mile lake.
