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Nature

Why Tullibees Matter: Conservation Conversation on Water Temperatures - Northern Waters Land Trust

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Northern Waters Land Trust
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This week we welcomed back the folks from Northern Waters Land Trust.  Our guests were John Sumption – Land Conservation Specialist and Annie Johnson Grants Manager/Conservation Specialist and board member Bob Karls. 

The Northern Waters Land Trust (NWLT) is a non-profit conservation organization working to protect water quality and preserve environmentally sensitive lands and water resources. Formerly the Leech Lake Area Watershed Foundation, NWLT serves the watersheds in Cass, Crow Wing, Hubbard and Aitkin Counties of Minnesota, and represents 2,235 lakes, 3,400 miles of rivers and streams, and nearly 4.2 million acres.

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Credit Northern Waters Land Trust
Tullibee or cisco

Some background on our conversation from NWLT and StarTribune today:

State wildlife managers became alarmed in 2006, when they noted tullibee kills in 18 lakes during temperature spikes in July according to Peter Jacobson a DNR fisheries biologist. That’s when they decided to launch a long-term project to use tullibee as a barometer for climate change.

Tullibee (also known as cisco) are a fish that some of us know about, but when I discussed with several lake associations on lakes that have tullibee in them most were not aware of them and few had ever seen one!  Some old timers and a few others fish them during the ice fishing season – but they are a significant forage fish in over 600 lakes in Minnesota and 48 high quality cold water lakes in north-central Minnesota.  NWLT has focused on a subset of these 48 lakes currently as part of its Clean Water Critical Habitat program. 

Warmer water fish include sunfish, crappie, bass, and many rough fish

Colder water fish include walleye, trout, and tullibee (also known as cisco) need colder water.  Long term warming of water in a lake and especially critical warm temperature during the peak of the summer can have fatal impacts on some species of fish.

Tullibee is the most tolerant cold water fish species and are a very important as a food source for predator fish like musky, pike and walleye.

In other words, if Tullibee can’t survive, then other fish won’t either.

But Tullibee won’t be alone. A major study published in the journal Science found that if greenhouse gases and average temperatures continue to rise at current rates, the world will see a major loss in diversity. One in six species around the globe could disappear because they can’t move or adapt fast enough to changing habitat.

Peter Jacobson, a fish biologist with the state Department of Natural Resources has been studying tullibee since heat-related fish kills first got his attention in the hot summer of 2006.

In the Minnesota lakes that are home to tullibee, it plays out like this. In deeper lakes, the water stratifies into layers of increasingly cold temperatures. When a lake gets hot at the surface, the tullibee go deeper. But they also need good supplies of oxygen, which can be scarce at the bottom. So they try to find that sweet spot that is cold enough (~64 degrees F) and has enough oxygen (2ppm and optimally 5ppm).

Longer summers result in less mixing of lake water layers, which means less oxygen makes it to the bottom. The tullibee get squeezed upward by low oxygen and then they encounter warm temperatures.

It’s not just the gradual warming — it’s also the sudden hot summer spikes.  Several lakes in our area saw temperature spikes in 2006 and 2012 and in lakes with tullibee there were significant die offs in those lakes with thousands of dead fish on the surface by early August.  While the eagles enjoyed an easy meal, it was a warning about how fragile the “fish food chain” is in our lakes and the impact that both climate change and also development of the watersheds around out lakes can be.

If tullibee don’t exist anymore, it doesn’t mean that walleye, musky and pike will disappear totally, but there will be fewer, smaller fish and the other species in the ecosystem will become their primary food source.

NWLT in 2021 I in its 7th year of a program to safeguard the clean, cold water that tullibee require by protecting 75 percent of the forests in watersheds surrounding clear-water fishing lakes from development or agriculture use.  NWLT are working with conservation groups including the Minnesota Land Trust, local governments and the DNR to protect this land.

Forests anchor land and keep it from eroding into lakes. Erosion-added phosphorous aids the growth of algae that depletes oxygen in the deepest waters of a lake, where tullibee live. Protecting forests to protect fish is a tactic we employ on lakes here in our north central lakes of Minnesota.