New Thriving Species: A warmer Lake Superior is causing fisheries to diversify their hatcheries as a larger variety of fish are beginning to thrive including the walleye (pictured above). Image: megankhines/Flickr
L'ANSE, Mich. — Long dedicated to the trout that sustain its commercial fishing, the Keweenaw Bay Indian Community started rearing fish that historically couldn't survive in much of frigid Lake Superior.
"We started raising walleye at the hatchery in 2005," said Evelyn Ravindran, a natural resource specialist with the tribe. "We see them more and more."
Commercial fishing has been a steady staple for the tribe over the past few decades. Walleye is a highly sought fish in the lower Great Lakes. And so the tribe, sensing a business opportunity, added that fish to its hatchery.
Lake Superior's chilly waters used to be too cold in most spots for walleye to live, but, spurred by warmer runoff and less ice, the lake has warmed far faster than predicted over the last five decades.
The change is offering more real estate for many fish.
Vulnerable to invasives
A warmer Lake Superior, however, has less habitat for some trout and is vulnerable to invasive species that already have drastically changed the other Great Lakes.
About 20 members of the tribe fish commercially, said Gene Mensch, a biologist with the Keweenaw Bay Indian Community's Natural Resources Department.
Trout fishing adds to the bottom line for the community, no question, said Mensch, though "you can't put a price tag on what it means" to some of the members.
The lake is warming faster than the atmosphere, said Jim Kitchell, a professor at the University of Wisconsin, Madison, and senior author of a new study examining the lake's fish. "Lake Michigan and Huron are warming but at half the rate [of Superior]."
More walleye, less chinook
Over the past 40 years, the large, deep freshwater lake has had an average water temperature increase of about 5 degrees Fahrenheit, partly due to a 50 percent ice cover reduction over the same time.
Such changes have increased suitable living areas for walleye by 223 square miles, one-and-a-half times the footprint of the city of Detroit. Chinook salmon and lean lake trout have seen habitat increase by 191 and 161 square miles, respectively, according to the study from Kitchell and colleagues.
Lake Superior, the largest of the Great Lakes, covers 31,700 square miles.
"We see the biggest changes in walleye, as 30 years ago they were limited to these very few little areas," Kitchell said. "They have expanded their habitat in enormous ways."
And fishing catch rates prove it. In 2012, charter boats on Lake Superior caught 7.3 walleye for every excursion, according to the Michigan Department of Natural Resource data. That number was 0.002 in 1998.
The warmer waters aren't good for all fish – habitat decreased 62 square miles for the siscowet – a fat, deep-water-loving lake trout.
Of the five Great Lakes, Lake Superior most closely resembles its fishery of 100 years ago – before invasive species altered the other lakes' rather dramatically. The lake, which touches northern Minnesota, Wisconsin, Michigan's Upper Peninsula and Canada, is more remote and sees less shipping traffic than the others.
Warmer temperatures could allow for invasive species to become a bigger problem, especially the blood-sucking sea lamprey, said David Jude, a fisheries research scientist at the University of Michigan, who was not involved in the study.
Sea lamprey are already present in the lake and mostly feed on lake trout.