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Climate change transforming where Great Lakes fish live

Sep 17, 2019 04:53AM ● By Editor

MDNR Resource Analyst Joe Nohner, left, prepares to anchor as Kevin Wehrly a fisheries research biologist with the MDNR's Institute for Fisheries Research marks their GPS coordinates on Cedar Island Lake in White Lake Township Tuesday, Sept. 10, 2019 as Research analyst from MSU Ken Yeh looks on.  © Mandi Wright, Detroit Free Press 

By Keith Matheny of The Detroit Free Press - September 16, 2019

Climate change is warming the waters of the Great Lakes and other lakes and rivers in the region — a big concern to scientists and fisheries managers, as few animals are more sensitive to temperature than fish.

Different fish species need different temperature ranges to thrive. And the region's warming waters are already causing fish population shifts, with the consequences not yet fully understood.

What fish can be caught where will continue to change over the next few decades — perhaps dramatically. And that will impact — and could harm — a vital economic driver in Michigan. Some 1.1 million anglers contribute $2.3 billion to Michigan's economy each year, through purchases of gear and clothing, booking hotel rooms, buying meals and more, the nonprofit Michigan United Conservation Clubs found in a study released in January

"If you like bass, things are looking good. But if you like walleye or cisco, things aren't looking as good," said Gretchen Hansen, an assistant professor at the University of Minnesota's Department of Fisheries, Wildlife and Conservation Biology.

At the Michigan Department of Natural Resources, and its counterpart agencies in Minnesota, Wisconsin and elsewhere throughout the Great Lakes region, planning for how to manage fisheries amid these significant shifts is already a matter of urgent study.

Region's air, water getting warmer

A popular sport fish in Michigan, walleye are considered a cool-water fish — for optimal breeding and growth, they want lake conditions warmer than trout, but cooler than bass and panfish. They're having trouble finding that anymore in southern Michigan's warming inland lakes, said Kevin Wehrly, a fisheries research biologist for the Michigan DNR's Institute for Fisheries Research in Ann Arbor.

"Historically, we've stocked walleye into inland lakes in southern Michigan, and there are many of those lakes that just don't support walleye any longer," he said.

"It's most likely water temperature. Water temperature is the main driver of most (fish) species' distribution patterns."

To the north, in Ontario, studies of fish populations in thousands of inland lakes show warm-water-loving species such as smallmouth and largemouth bass are making their way into northern lakes where they've never been seen before. Those newcomers could stress the fish that already make those lakes home, as they compete in many cases for the same habitat and food.

Air temperatures in the Great Lakes region have warmed faster than the rest of the United States — by 1.6 degrees Fahrenheit between 1901-1960 and 1985-2016, as the rest of the contiguous U.S. warmed only by 1.2 degrees. By the end of the 21st century, global average temperatures are expected to rise an additional 2.7 degrees F to 7.2 degrees F, depending on future greenhouse gas emissions, with corresponding changes in the Great Lakes region, a report by 16 researchers around the Great Lakes Region, sponsored by the nonprofit, Chicago-based Environmental Law and Policy Center, found earlier this year.

Kevin Wehrly is a fisheries research biologist with the MDNRs Institute for Fisheries Research lowers a Secchi disc before doing water quality testing at Cedar Island Lake in White Lake Township Tuesday Sept 10 2019Kevin Wehrly is a fisheries research biologist with the MDNR's Institute for Fisheries Research lowers a Secchi disc before doing water quality testing at Cedar Island Lake in White Lake Township Tuesday, Sept. 10, 2019.  © Mandi Wright, Detroit Free Press 

The Great Lakes have warmed faster than the surrounding air in recent years, according to the Great Lakes Integrated Sciences and Assessments Program (GLISA), a collaboration of the University of Michigan and Michigan State University funded by the National Oceanic and Atmospheric Administration, part of a national network that focuses on adaptation to climate change and variability.

That warming impacts local waters as well. Summer surface water temperatures on the coldest Great Lake, Lake Superior, increased approximately 4.5 degrees F from 1979 to 2006, a significantly faster rate than regional atmospheric warming. Declining winter ice cover is the largest driving factor, according to researchers.

The 'double-squeeze' on cold-water bottom fish

In deeper lakes, summer temperatures cause water to form distinct temperature bands, warmer near the surface and colder below, a phenomenon called thermal stratification. Warming makes that process stronger and longer-lasting, and oxygen can't permeate those thermal layers to reach the bottom.

Historic weather records also show climate change is leading to stronger spring storms that spur nutrient runoff from farms and lawns, which, in turn, fuel algae blooms in lakes. When those blooms die in a lake, they sink to the lake bottom and remove oxygen. The layers prevent a replenishing of the depleted oxygen, creating hypoxic "dead zones." The dead zone in algae-challenged Lake Erie from this phenomenon, every summer into fall, can be more than 6,200 square miles.

"There's an example of a Great Lake where you've already seen, partly through warming and the (depleted oxygen zones) in the central basin, you already see cold-water fish isolated in the eastern basin and not really found much in the other parts of Lake Erie," said Brian Shuter, a professor in the University of Toronto's Department of Ecology and Evolutionary Biology.

For fish that need cold, deep water, like lake trout, the lack of oxygen at the lake bottom pushes them closer to the surface, into temperatures and habitats that aren't optimal for them to thrive, Wehrly said.

"We call that a temperature-oxygen squeeze," he said. "They're limited by temperatures from the top, and they're limited by oxygen depletion on the bottom."

Cisco, a lake herring species native to Michigan, prefer cool-to-cold, deep water.

"We had about 153 cisco lakes in the state historically" out of Michigan's 11,000 inland lakes, Wehrly said. "We've lost a number of those populations because of that total loss of oxygen in the cold water portion of the lake during the summer."

Fishing through big data

When Karen Alofs looks to see how fish populations are changing in Ontario lakes, she doesn't use waders and nets. She uses a computer and big datasets.

Alofs, an assistant professor of applied aquatic ecology at the University of Michigan's School for Environment and Sustainability, has spent the past several years, going back to her days at the University of Toronto, studying how warming waters in the northern Great Lakes region might be affecting where fish live.

Fortunately for her, the Canadian province of Ontario offered a great way to check: data from fish surveys in 1,527 inland lakes, taken both decades ago, between 1957 and 1986, and again more recently, between 1983 and 2011. The surveys for each lake, on average, were about 29 years apart.

Crunching the numbers, Alofs landed a big finding: The northern range of warm-water-loving sport fish such as largemouth and smallmouth bass, bluegill and pumpkinseed is shifting farther north, and rather dramatically: from 8 to almost 11 miles per decade.

"The large-bodied sport fishes were the ones that had the largest shifts in their distributions northward," she said. "For example, smallmouth bass is one of the species that's expanding north, and now occurring in lakes in northern Ontario that were previously too cold for them."

Kevin Wehrly a fisheries research biologist with the MDNRs Institute for Fisheries Research takes a sample of water out of Cedar Island Lake in White Lake Township Tuesday Sept 10 2019Kevin Wehrly a fisheries research biologist with the MDNR's Institute for Fisheries Research takes a sample of water out of Cedar Island Lake in White Lake Township Tuesday, Sept. 10, 2019.  Photo:  © Mandi Wright, Detroit Free Press 

Research shows the fish expand their range via human stocking by government agencies or fishing clubs; naturally through connected waterways and drainage networks, and by illegal introductions by anglers and lake residents, or from bait-bucket transfers.

While bass expanding their ranges farther north sounds on its face like good news for bass fishermen, it's more complicated than that.

In the northern lakes where warm-water predator fish like smallmouth bass are establishing themselves, small prey fish — we'd call them minnows, Alofs said — decline, and are more likely to vanish from lakes. Brook trout also tend to decline, she said, as the bass compete for the same food.

The loss of prey fish not only potentially impacts the cool- and cold-water species of fish already living in northern lakes, it could cause an eventual crash in populations of the bass now gaining a foothold.

"Bass are extremely efficient predators in warm water," Shuter said. "They pretty much clean up the feeder fish that lake trout also rely upon."

The vast Great Lakes have more space and habitat range for fish to find a way to limit the impacts of new stresses, but that's harder for them to do on other lakes, Hansen said.

"Range expansions, when we're talking about inland lakes, are tricky things to think about," she said.

Managing a shifting population

How to manage fish populations, and preserve a multi-billion-dollar sport fishery, in the changing environment of the rest of this century will not be simple.

"We're trying to be proactive as an agency, trying to understand what waters are vulnerable, what species are vulnerable — and likewise, what waters and species are resilient — and shift our management decisions accordingly," Wehrly said.

"Certainly, as warm-water species become more abundant, that's what you're going to catch more of. We have many of those species already in the state. The southern part of the state is already dominated by warm-tolerant species. What we'll see is just a shift in where that line is in the state."

The DNR is currently trying to pull together Michigan's archive of fish survey data from lakes, to look at historical changes over time in a similar way to how Alofs has in Ontario, Wehrly said.

Researchers say the emphasis will become highlighting lakes and rivers better equipped for stressed fish populations to withstand warming waters, and targeting efforts there — "protecting those places we think are going to be the strongholds for many of these species," he said.

There are some lakes where "it's clear that the climate is not going to be suitable anymore," Alofs said, without naming names. 

"And then there are some lakes where the climate may be all right, and if we protect these fish from other stresses, like overexploitation or pollution, we might ensure they can make it through those really warm years," she said.

a small boat in a body of water MDNR Resource Analyst Joe Nohner prepares to dock the boat after running tests with his team at Cedar Island Lake in White Lake Township Tuesday Sept 10 2019Joe Nohner prepares to dock the boat after running tests with his team at Cedar Island Lake in White Lake Township Tuesday, Sept. 10, 2019.  Photo:  © Mandi Wright, Detroit Free Press MDNR Resource Analyst 

Things could become as outside-the-box as lake-by-lake catch limits, Alofs said. 

"Targeting bass over walleye in certain lakes may actually favor the long-term viability of the walleye population," she said. "These are all management tools we are thinking about right now."

Alofs is also collaborating with Wehrly on examining walleye fry, or juvenile fish, as they grow in rearing ponds throughout the two peninsulas of Michigan, before they are stocked in state lakes in late spring and early summer or fall.

"These fish are being raised at a variety of different temperatures," she said. 

The researchers want to check the metabolic rates of the fish — how their bodily processes work —at those different water temperatures, for both Lower Peninsula and Upper Peninsula walleye stocks.

"We hope to better understand whether those fish are better adapted to those temperatures, and how temperature might impact the survival of those fish," she said.

The Great Lakes region's fish are vital to our way of life, Alofs said — as a sustainable food source, for angling and its impact on the economy, and from a cultural perspective. But our freshwater fish species are more threatened than most of their fellow animals on land or in the ocean, she said.

"They accumulate all of these stresses: climate change, pollution, invasive species, habitat destruction," she said. "We have less of a body of knowledge to work with to understand the declines of the habitats we see. 

"Fish can act as a canary in the coal mine, and be indicators of environmental problems as they emerge."

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