A warmer and wetter climate in the Midwest could lead to the displacement of some cold water fish species in southern Lake Michigan and trigger mass die-offs in smaller inland lakes, according to a report published this week by Purdue University.
As the atmosphere warms due to the proliferation of greenhouse gases, so too are the Great Lakes, warns a Purdue University-led report on the impacts of climate change in Indiana. Summer surface water temperature in Lake Michigan has warmed about 3 degrees since 1980, and is projected to accelerate, rising at least 1 degree a decade, experts say. A hotter climate could become a problem for some game fish, like trout and salmon, that depend on cold, oxygen-rich waters.
â€śI think it might be a surprise to a lot of people that Lake Michigan is warming,â€ť said Tomas Hook, a professor of fisheries and aquatic sciences at Purdue and director of the Illinois-Indiana Sea Grant.
The warming is expected to reduce the amount of time cold water fish spend in the southern basin of Lake Michigan, where the chance of catching these species is already limited because itâ€™s shallower and more tepid than the rest of the lake. Now, much of the lake is so deep and cold in open water that most fish canâ€™t survive there, but warming will likely open up more habitat for the majority of fish, Hook said. However, whether they will be able to find sufficient food in those new waters is unclear.
â€śWith water heating up, species, particularly ones who prefer cold or cool water, their body temperature is dependent on the temperature of the water,â€ť said Karen Murchie, a research biologist with Chicagoâ€™s Shedd Aquarium. â€śThey can behaviorally select where they want to live, but they could potentially be squeezed out of where they want to live and where they want to go. This resonates, not only with Indiana waters, but all of the Great Lakes.â€ť
â€śTemperature is a master factor when it comes to fish,â€ť Murchie said. â€śItâ€™s so important and thatâ€™s why itâ€™s such a concern.â€ť
Milder water temperatures are expected to expand the range of warm water fish like bass, which are confined to southern Lake Michigan.
â€śBass fishing should be better,â€ť said Paul Labovitz, superintendent of the Indiana Dunes National Lakeshore. â€śBut if Iâ€™m a salmon fisherman, Iâ€™m going to be really disappointed when the lake warms up. Those are real impacts that people see right now. This isnâ€™t a 50- or 100-year thing. This is happening right now.â€ť
To withstand warmer temperatures, cold water fish, like chinook salmon, will expend more energy and require more food. In Lake Michigan, invasive mussel species have decimated the abundance of plankton, small organisms that serve as base of the food chain and the staple of many small fish diets. In doing so, the mussels cleared up the lake, but theyâ€™ve also contributed to the decline of the chinook salmonâ€™s primary prey, a small fish known as the alewife, whose population has crashed in the past several decades.
The breakdown in the food chain and the warming temperatures have been on the minds of fishermen, including Chad Kirkman, 32, of Chesterton. While Kirkman said heâ€™s not too concerned with the overall makeup of fish in the southern end of the lake, nodding to the healthy numbers of carp, channel catfish and bass, he has noticed the toll that warmer waters can take on steelhead when they return to spawn in Indiana tributaries in June.
â€śIf you hook one of them out there, you pretty much have to keep them, because the water is like 60-something degrees and they canâ€™t take it,â€ť Kirkman said. â€śItâ€™s like a person trying to run a marathon when itâ€™s 120 outside â€” itâ€™ll kill you. A lot of times after you take them off the hook, thereâ€™s no point in putting them back in the water because theyâ€™ll just flounder around and die.â€ť
If summer heat continues to spill into fall, anglers like Carl Beutler, of Westfield, Ind., also wonder about the impact of long-term temperature shifts.
On a recent weekday, after winds churned up colder waters in parts of Lake Michigan, Beutler and his son Joseph Oakman were among several fishermen who cast their lines along the lakefront pier in Portage, Ind., hoping for king salmon, expected to be in the area for spawning, to bite. But like most of the others, they left empty-handed.
â€śItâ€™s something everybody is concerned with,â€ť Beutler said about climate change. â€śShort-term, it will just reposition where the fish are at. Long-term, repercussions could be the destruction of spawning habitat, because they need a lower temperature to spawn. If the water temperatures increase, they are going to deteriorate before they even hatch.â€ť
The situation may be even more dire for cold water species inland, however. In addition to warmer waters, more frequent heavy precipitation could increase agricultural runoff and induce more algal blooms. When that algae dies near the lake bottom, it becomes food for bacteria, which deplete oxygen levels in deep, cold waters. This places cold water fish in a vise between warm surface water they canâ€™t tolerate and deeper cool water with little oxygen. Perhaps no other species underscores the severity of the issue than the cisco, a cold water whitefish that was once found in about 50 lakes in Indiana, but now remains in only six, Hook said.
Researchers say more algae blooms are likely for both ecosystems, although inland lakes are most at risk. There, cold water fish have to occupy a shrinking area as water warms near the surface and oxygen levels drop near the lake bottom.
â€śThey canâ€™t really migrate much but up and down in the water column,â€ť Hook said. â€śI would expect to see more die-offs in those types of systems. A lot of aquatic species donâ€™t have the flexibility to migrate into new systems like terrestrial organisms do.â€ť
The lack of oxygen typically persists until fall, when warm water cools and can mix with deeper water. With springlike temperatures arriving earlier and summer temperatures lingering into fall, the Purdue report warns that warming climate could prolong the period when there is less oxygen in the deeper water.
Temperatures in Illinois and Indiana have risen more than 1 degree over the past century, but scientists expect the warming to accelerate. Summer temperatures in Illinois could resemble Texas or Oklahoma by the end of the century, according to the U.S. Environmental Protection Agencyâ€™s archives.
The statewide average temperature for Illinois this summer was 75 degrees, 1.4 degrees above normal. This summer, Lake Michigan was measured at about 5 degrees above its long-term season average.
At a recent meeting in Portage to discuss the report, Labovitz, the national lakeshore superintendent, remarked about the changes heâ€™s noticed. The Indiana Department of Natural Resources has received reports of armadillo sightings. Beach season has unofficially extended into October. And, he is trying his luck growing sweet potatoes, a crop harvested in Southern states and California.
Hook, the Sea Grant director, said state resource managers have been accounting for short-term considerations, like invasive species or pollution, but the new study â€” part of a series of reports detailing the far-reaching impacts of climate change in Indiana â€” recommends they account for climate change by incorporating strategies such as pumping oxygen into the bottom of some small lakes.
Because these are such complex systems, itâ€™s difficult for even experts to predict what the end result will be, said Jeffrey Dukes, director of Purdueâ€™s Climate Change Research Center.
â€śThe bottom line is that these sort of changes are already happening,â€ť Dukes said. â€śWe already have things that are stressing aquatic ecosystems, and this is only going to increase the stress for many species. We donâ€™t know how many are going to deal with the changing climate on top of everything else. Itâ€™s going to cause problems for cold water species, but itâ€™s going to mix things up for all species.â€ť