Outdoors: Fish die-off in Lake St. Clair not surprising
If you look at gizzard shad twice, they die.
It’s no surprise that they’re often the first fish to show signs of disease or distress.
These delicate silvery fish recently have made headlines for large die-offs due to what the Michigan Department of Natural Resources recently confirmed as viral hemorrhagic septicemia (VHS), a fish pathogen which causes internal hemorrhaging.
Infectious virus causing large fish die-off on Lake St. Clair
It looks ugly, but don’t be alarmed.
In 2006, gizzard shad, blue gills, black crappie, muskies, freshwater drum and yellow perch died by the multitudes. Lake St. Clair was rife with dead shad, bass, muskie and perch in the spring of 2009. In 2011, there were reports of huge gizzard shad die-offs, and bass died due to co-pathogens from VHS. In 2013, they were reported in nearby Lake Erie.
Each of these years had something in common that eventually stopped the spread of the disease: the water warmed up past 60 to 65 degrees. VHS is a virulent pathogen, but it thrives in cold water. Once the waters become temperate, biologists say the danger is over. Lake St. Clair’s water temperatures are just hitting 60 degrees. The virus can still be there in reservoirs, but research shows it has never been known to cause disease in water above 64 degrees.
Though the virus dies in warm temps, gizzard shad boom with warm summers and mild winters. And anyone who tried ice fishing Lake St. Clair this winter knows they had to bring their own ice: the conditions were right for a population boom.
When shad get crowded, it stresses them and they become vulnerable to existing pathogens, such as VHS.
“It’s like sardines in a can if they’re concentrated together in the canals and it means less food for each individual fish,” said DNR research biologist Jan Hessenauer, who works on Lake St. Clair. “We also had a quirky spring a couple 60-, 70-degree days, those temp changes cause a lot of stress for fish. It makes them vulnerable.”
Hessenauer isn’t surprised by the recent outbreak.
“Fish acquire immunity from exposure to diseases. The last outbreak we had was in 2011 and those fish are getting older, aging out. It’s time for a new exposure to the disease.”
But the concern isn’t just about dead shad. Any angler worth their salt knows that shad are baitfish, with endless lures designed to mimic this fishy fare. Therein the danger lies: a vulnerable shad looks delicious to other fish on the foodchain, including muskies, pike, walleye, and bass, all of which can contract VHSv.
In 2006, VHS took a bite out of the musky population, but it recovered quickly. However, the situation wasn’t so pretty in New York’s Thousand Islands.
“Biologists there told me that VHSv really put a dent in their musky,” said Gary Whelan, fisheries project manager for the DNR. “The virus can hide a long time in fish. It’s no different than herpes, which can go unseen for years, but when there’s a stressor it will emerge. The large populations of gizzard shad represent a stressor. Humans and fish, we all have the same type of immune systems. When we’re healthy we can fight off diseases. But when our body has been battling something, like cancer, then we might go into the hospital and die of pneumonia. So, it might not be VHS that kills the fish, it could be some other opportunistic pathogen stepping in which is not normally a problem,”
“Most of the fish will fight VHS off and survive. So, it’s rare to see a population-level effect. We didn’t have one last time, but we want to know if there are going to be population level effects.”
It’s the anglers who help with that, said Whelan. Biologists can’t be everywhere. Michigan has less DNR personnel and financial resources per water acre than any other state, according to fisheries chief Jim Dexter. Citizen eyes and ears make a difference.
“People have been sending us photos and it looks it’s taking the same course as last time. We’re hearing a few reports about bluegills, largemouth bass, yellow perch and even a report of one musky,” said Whelan. “We’re asking the public to keep an eye on it.”
He says kills of more than 25 fish are something to be concerned about. “If it’s just a couple fish, it could be anything.”
He explains that every spring, there are fish die-offs, regardless of VHS. People panic. Usually, it’s normal spring die-off.
Spring die-off occurs due to various stressors. Fish come through the winter waning in strength because they’ve been eating less. As the water heats up, their metabolism rises and they direct energy to spawn, which can be strenuous.
Lake St. Clair homeowner, avid angler and musician Matthew Shafer, who is best known by his stage name “Uncle Kracker,” isn’t worried. He grew up on the lake.
“There are tons of them up and down where I live. It’s spring. It happens. Water warms up, some don’t make it,” said Shafer. “People are losing their marbles over it.”
“The public can provide the reports to our fish kill email address at DNR-FISH-Report-Fish-Kills@michigan.gov,” Whelan said. “This information helps us track this event and determine where best to collect additional samples.”
Anglers are reminded to refrain from moving live fish between water bodies and to properly dispose of bait. Boaters need to make sure their bilges and live wells are emptied prior to leaving a boat launch, and equipment must be cleaned and disinfected after use. Visit michigan.gov/fishing for more information on how those who fish and boat can help limit the spread of fish disease and invasive species.