Climate change could drive native fish out of Wisconsin waters

The cisco, a key forage fish found in Wisconsin’s deepest and coldest bodies of water, could become a climate change casualty and disappear from most of the Wisconsin lakes it now inhabits by the year 2100, according to a new study.

In a report published online in the journal Public Library of Science One, researchers from the University of Wisconsin–Madison and the Wisconsin Department of Natural Resources project a gloomy fate for the fish — an important food for many of Wisconsin’s iconic game species — as climate warms and pressure from invasive species grows.

In the case of the cisco, a warming climate poses a much greater risk than do exotic species such as the rainbow smelt, the invasive that most threatens the deep-dwelling cisco by eating its eggs and young, the Wisconsin researchers say.

“By 2100, 30 to 70 percent of cisco populations could be extirpated in Wisconsin due to climate change,” says Sapna Sharma, a researcher at the UW–Madison Center for Limnology and the lead author of the new study, which predicts the decline of the cisco according to a number of possible future climate scenarios. “Cisco are much more at risk due to climate change rather than interactions with exotic species.”

The cisco, sometimes called lake herring, is now found in about 170 inland lakes in Wisconsin. A member of the trout and salmon family, it is also found in the Great Lakes and once formed the basis of an important commercial fishery before overfishing and the invasion of the alewife, rainbow smelt and sea lamprey caused its populations to diminish dramatically.

Sharma described the cisco as a sentinel species: “It’s one of the most vulnerable fish species in Wisconsin because it depends on cold water,” says Sharma, an aquatic ecologist and statistical modeling expert. “Cisco aren’t the most important socioeconomic species out there, but they are a good indicator of water quality.”

From an ecological perspective, when fish species are displaced by changes in water temperature or for other reasons, it opens the door to other species, especially exotic invasives. The ecological niche occupied by the cisco is also favored by the rainbow smelt, a foreign species that has been in the Great Lakes for decades but that is only now making its way into Wisconsin’s inland lakes.

“The range expansion of invasive species with climate change could be a problem,” Sharma explains. “It could change the composition of species we’re familiar with in Wisconsin. It may be that just a few species dominate. The species composition wouldn’t just be different, there could also be less biodiversity.”

In addition to the ecological change that would be prompted by a warmer Wisconsin climate, Sharma notes, the impoverishment of aquatic ecosystems will have potential socio-economic implications, especially in a setting like Wisconsin where recreational fishing is an iconic pastime, not to mention an important industry.

“This could very well impact the fishing experiences we have,” avers the Wisconsin researcher.

In addition to Sharma, co-authors of the new Public Library of Science One report include M. Jake Vander Zanden and John J. Magnuson, also of UW–Madison, and John Lyons of the Wisconsin Department of Natural Resources.