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In a report published in the online journal Public Library of Science One, researchers with UW-Madison and the Wisconsin Department of Natural Resources predicted a gloomy fate for cisco, a key forage fish that serves as food for many of the state’s iconic game species.

Cisco — often called lake herring — are found in the state’s deepest and coldest waters, but researchers say that warmer waters and increased presence of invasive species are now threatening the fish’s habitat and survival within the state.

Researchers found that a warmer climate poses a greater risk to cisco than the invasive species rainbow smelt, which devours the native, deep-dwelling fish’s eggs and young.

Still, the study says the exotic predator is not the biggest threat to the species’ continued presence in Wisconsin waters. According to Sapna Sharma, a researcher at the UW-Madison Center for Limnology and the lead author of the study, its sensitivity to warming could reduce the species’ population drastically.

“By 2100, 30 to 70 percent of cisco populations could be extirpated in Wisconsin due to climate change,” said Sharma. “Cisco are much more at risk due to climate change rather than interactions with exotic species.”

Currently, cisco — a member of the trout and salmon family — is found in roughly 180 lakes in Wisconsin as well as the Great Lakes, mostly in the northern regions of the state.

“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.”

At one time, the species was a base for a commercial fishery before overfishing and invasive species — including rainbow smelt, the alewife and sea lamprey, reduced its populations significantly.

Researchers warned that if the species is displaced by changes in water temperature, it could further root the invasive species in the state’s ecosystems, since the rainbow smelt would likely occupy the ecological niche left behind.

“The range expansion of invasive species with climate change could be a problem,” Sharma explained. “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.”

Sharma said that, in addition to ecological changes, a warmer Wisconsin climate could have socio-economic effects on the state since recreational fishing is both an iconic pastime and industry.

“This could very well impact the fishing experiences we have,” Sharma said.

Additional Information:

• Comparing Climate Change and Species Invasions as Drivers of Coldwater Fish Population Extirpations