GREAT OUTDOORS: Common spring fish diseases lead to angler concerns

About a week ago, I received a fretful call from a licensed charter boat captain friend of mine relaying news that he just heard of a 20 million fish winter-kill of walleyes in Lake Erie off the New York shoreline. It got my immediate attention, as I wondered if last fall's storm force wind events decimated bait fish availability, impacted walleye gills with mud or had some other unexplained effect on their well-being. However, it was a big relief when I checked with Eric Weimer, supervisor of the Ohio Division of Wildlife Sandusky Fisheries Research Station, who confirmed that an alewife die-off did occur last spring but no 2026 fish kills have been reported yet. Another "Fakebook" rumor put to rest... Alewives invaded the Great Lakes after the Welland Canal was opened to bypass Niagara Falls, previously as far as they and other Atlantic Ocean species could ascend. Mass mortality events occur when their metabolism speeds up after water temperatures rise in the spring and summer in the absence of enough prey. You may recall that after years of public work crews and volunteers toiling to clean millions of alewives off the shorelines of Lake Michigan, experimental stockings of Pacific salmon were introduced to prey on them to suppress their numbers. Related to alewives, gizzard shad die when water temperatures drop too low. A southern species that may have gained access into the Great Lakes via the Ohio-Erie Canal, the majority die when water temperatures drop in the winter but are often seen floundering during the early spring. Viral Hemorrhagic Septicemia (VHS) was first confirmed in Lake Erie in 2006 when thousands of freshwater drum, yellow perch, gizzard shad, walleye and other species perished from it. Hundreds of dead muskies from Lake St. Clair carried downstream in 2005 were seen floating in Lake Erie and lying along shorelines. Visible symptoms include bulging eyes, open sores and bloody internal organs. VHS usually disappears when water temperatures exceed 59 degrees. In 2023, thousands of dead bluegills and a limited number of a few other species surfaced all around east and west harbors from VHS. A skin disease commonly found on walleyes that appears as raised, wart-like tumors is called lymphocystis, nicknamed cauliflower disease or fish herpes. While usually not fatal to walleyes, many anglers elect to throw those with severe cases back rather than take a chance that the sores on the head and scales, which do not penetrate into the meat, will make them sick (they won't). It is prevalent in the spring when fish spread it while they are concentrated while spawning. I have frequently seen bass with cottony white, then brown or black fuzzy patches across their backs from an often-fatal fungal infection called saprolegnia. It can develop after they have been landed with an abrasive net, poorly handled or kept out of the water too long, especially while it was already under stress from guarding its nest during spawning season. Most fishermen know that salmon die after spawning, but other species of fish are sometimes fatally weakened from the combination of disease and spawning. Smelt have a species-specific parasite called glugea hertwigi that creates cysts in their gonads and intestines that commonly lead to post-spawning mortality. When I worked at Stone Lab, I would get calls in April about "millions" of dead baby walleyes floating on the water between Kelleys and Pelee islands. It never hurts to check, but each time I did, the "baby walleyes" would turn out to be mature smelt that died after spawning.