Tower Area Fisheries Supervisor Keith Reeves discussed the future of Minnesota’s cold-water fish species at an event hosted by the Ely Field Naturalists on Wednesday.
Temperatures across the state have consistently trended upwards over the past several decades, leading to increased lake surface temperatures, plus a longer warm season and extended periods of stratification. These conditions are less favorable for Northern Minnesota’s cold-water species, especially heat-sensitive species such as lake trout, which do not fare well in water above 48℉.
Looking at data from Mendota, Reeves said, the water temperature reached around 72℉ one summer and the local cisco population plummeted and never recovered.
“All the fish died, they had a summer kill, and they’re all gone. And then they didn’t have any fish after that. I think it was just because it got that warm. They might not have gone if the temperature was a degree or two colder than that,” he said.
“Why would we protect fish? It’s just fish, right?” said Reeves, “But they’re like a canary in the coal mine. We know if these fish go away, it’s because the habitat is going away.”
“If you’re protecting that cold-water habitat, you’re protecting the very best of our environment,” Reeves continued, “So not everything’s just a warm water pond, but now you have diversity.”
Reeves displayed a map outlining various conservation strategies across the state. For now, most of the Boundary Waters locale stands in the “vigilance” zone, meaning wildlife managers and researchers will “watch and measure and make sure things aren’t happening out there,” said Reeves. Much of the rest of St. Louis County stands in the “protection” phase, which requires a bit more action.
“This (strategy) puts better protections on the habitat, cold-water habitat, to prevent it from being eroded,” said Reeves, “In the lower part of the state, well, we can do some thinking, but it’s not going to bring the cold-water habitat back.”
He says the focus now is on North Central Minnesota, including Cass, Aitkin, Hubbard, and southern Itasca County, “where there are ways to save things, to manage, to protect environments.” This can include the creation of refuge lakes, or lakes of biological significance, where efforts can be concentrated to help species thrive.
Sampling and monitoring efforts have ramped up since 2022 to better understand local fish populations. Wildlife researchers may take samples with gill nets or, in some of the deeper trout lakes, nets that reach up to 50 feet down. In other conditions which don’t allow the use of a net, samplers may simply go fishing.
Reeves emphasized the importance of conservation to maintain Northern Minnesota’s unique array of cold-water fish.
“If you protect the environment, you end up with cleaner water and good habitat,” said Reeves, “We have great stuff up here.”
