The Michigan Department of Natural Resources (MDNR) is investigating a fish die-off – particularly of gizzard shad – that have been reported by citizens around Lake St. Clair.
Government officials in Michigan say a number of samples have been collected to determine the cause.
Some of the fish may have been affected by viral hemorrhagic septicemia virus (VHSv), a very contagious pathogen, but the DNR is still waiting on confirmation.
“Thanks to the public’s vigilance we are able to get timely samples from these fish mortalities, and it is very likely VHSv is involved,” stated Gary Whelan, research program manager for the DNR’s Fisheries Division.
“VHSv has been detected in these waters since at least 2003, and when conditions are right the pathogen will cause disease events like this one.”
Dave McCready, owner of Ed’s Bait in Wallaceburg, told the Sydenham Current he is skeptical about the reports.
“I would honestly wait to see some research from the Ontario Ministry of Natural Resources and Forestry and MDNR,” McCready said.
“Shad die off every year, so I wouldn’t be too alarmed about it. For some reason it seems to be gaining some publicity this year.”
McCready added: “We haven’t been seeing VHS signs in the walleye, perch or bass.”
Ministry of Natural Resources officials told the Sarnia Observer back in 2011 that they believed a massive die-off of gizzard shad was a natural occurrence in January that year.
Officials said the die-off that year was likely a result of temperature shock, after a warm weekend, followed by cooler temperatures.
Government officials in Michigan say many of the collected fish showed the classic external signs of VHSv: bloody patches on the skin. VHSv first caused fish mortalities in the St. Clair-Detroit River corridor in 2006 and occasionally has been detected in these waters since that time, DNR officials say.
The virus is known to infect more than 30 species of Great Lakes fish and has been found in lakes Superior, Huron, Erie and Ontario, along with a few inland lakes.
Some species such as lake sturgeon and walleye are very resistant to it and others such as bluegill, largemouth bass, muskellunge, gizzard shad and round goby are very susceptible to the virus, government officials in Michigan said.
The pathogen causes the fish’s blood vessels to leak, which is why the skin shows bloody patches. This symptom is shared with other pathogens, so testing is needed to confirm if VHSv is involved. Previous research has shown that many fish recover from this virus infection, although there is no treatment.
“The public is encouraged to continue to provide us with reports of fish kills with a focus on kills of more than 25 fish,” Whelan said.
“The public can provide the reports to our fish kill email address at DNR-FISH-Report-Fish-Kills@michigan.gov. This information helps us track this event and determine where best to collect additional samples.”
MDNR officials said anglers are reminded to refrain from moving live fish between water bodies and to properly dispose of bait.
