A couple months back I sat down with Assistant Professor of Biology at Winona State University Dr. Jennifer Biederman to discuss trout, trout streams, invertebrates and the research going on in the driftless area. Dr. Biederman lives near Winona on a local trout stream I am quite fond of. She received her BA from St. Mary’s University and her PhD from the University of Minnesota. Currently she teaches classes at WSU and has written papers on the subject of brown trout feeding habits in ground water streams and has contributed to other papers looking at brown trout growth in the driftless area.

I sat down with her after contacting Dr. Neal Mundahl who suggested that Dr. Biederman would be a good resource to help answer some of the questions I had regarding invertebrates, habitat and climate change in the driftless area. I should preface this by saying that this is the first interview I’ve ever done, it was more challenging than I expected and that Dr. Biederman was an excellent sport who took time out of her busy life to sit down with a local trout geek for an hour to talk bugs, fish and the state of the driftless area. Thank you Dr. Biederman.

A couple general things I learned from this interview are:

  • Trout in the driftless area grow faster than trout in other streams given the abundance of food in the harsher times of the year.
  • It is thought that one of the main contributors to that growth is the abundance of winter emerging midges in southeastern Minnesota.
  • As with most places climate change could significantly affect the driftless area and specifically the trout population which is a terrifying thought for me. According to a 2011 study by the Wisconsin DNR1, a 5°F increase in air temperatures could potentially wipe out brook and brown trout populations in the driftless area.
Diamesa: The Winter Emerging Midge

Do you have a favorite invertebrate?

I don’t know that I have a favorite but one has kind of grown on me. There’s a type of midge that is winter emerging, I’m sure you’ve seen them out there. They are in the genus called Diamesa, and taxonomically speaking they are still not well understood and there’s a lot of these out there. Some of them emerge in the winter, and some emerge in the spring, but the ones that emerge in the winter, I think they’re cool. They feed trout in the winter when there isn’t a lot of other food available.

Are they (midge) the most prolific biomass in the streams?

In general on most streams that I’ve worked on yes they are the most biomass available in terms of food and they are also the food that they (the trout) consume the most. When you look at what food contributes the most in terms of calories, they (midges) aren’t always the most important. The Scuds and snails are actually calorie-wise pack more of a punch. It’s like eating an apple pie versus like a bran muffin or something. But the fact is is by volume they are still eating tons and tons of midges, especially at times of the year when other aquatic invertebrates might not be as available such as in the winter.

What kind of field work are you involved with?

Recently I’ve had a hiatus with doing a lot of field work but I’ve been doing a little bit with bioenergetics modeling, which basically looks at the trout, and how the water temperature influences the trout and how they grow given what they’re eating. So we look at the nutrition of all the food their eating, look at the water temperatures and we’ll kind of see, if the water temperatures are X in the middle of summer and trout are eating Y then how fast should they be growing and use that information to model the future with regards to climate change. So if the water temperatures go up the trout have a higher metabolic demand and thus they’re going to have to eat more in order to grow at the same rate.

We’re also doing some work on the Whitewater river where we’re looking at better ways to deal with big rainfall events. If you remember a couple years ago when there was a big trout kill off on the South Branch of the Whitewater River, this work is actually in response to that event. We had a large fish kill, the response is really slow and by the time anyone got there to look at the water, the waters gone. And so what this project is going to do is it’s going to look at how we can better respond in situations when there are these massive rainfall events in a watershed like the Whitewater where it’s heavily agricultural and very vulnerable when there’s large rain events.

Part of the project is looking at what the baseline conditions are, the invertebrate communities, the fish populations in different reaches and the baseline stream conditions then monitoring for rainfall events. We are working with the geomorphologist at WSU to monitor water conditions and working with local individuals to help sample and monitor after rainfall events. There are going to be six sites throughout the White Water Watershed.

Stomach Contents: Midge Larvae

What other interesting research is being done in our area?

Len Ferrington has been doing some stuff in the lab at the UofM and trying to make some projections based on climate change. Specifically with the reproduction of the winter emerging midges and consequences if water temperatures warm up even a few degrees which could wipe out these midges. This could be of big consequence to trout in the driftless area because one thing that we are finding is that unlike trout streams in similar latitudes in other parts of the world, the trout here grow really fast. Part of the reason for that is that they grow a lot during winter and spring. Whereas traditionally you kind of think of winter and spring as being a time when a lot of fish just kind of stopped growing or are just maintaining. They might even lose weight a little bit because conditions are harsher for them metabolically.

Where are we at in terms of climate change with regards to trout and invertebrates in southeast Minnesota?

I don’t know if I could speak to recent changes or observations based on long term trends but I know in the short term future things people are a little concerned. I would say partly because right now where Winona is or the driftless area in general we’re kind of at the margin in terms of the temperature tolerances that trout can handle. So if we get any warmer, that’s when trout are gonna become stressed out. If we kind of plot the annual temperature of our streams it doesn’t change a whole lot because they’re spring fed but in the winter time, which is a time when trout seem to be growing really well, part of the reason for that is they probably have a lot of food available like those winter emerging midges. Another reason is that the temperature profile of the streams where they’re growing fast in the winter, the temperature is perfect for them to be growing so if those temperatures start to warm up a little bit what’s going to happen is metabolically they’re going to need to have more food to eat. More food in order to grow and if there’s less food available the scenario could be bad. So if there are fewer midges available, because of warmer water temperatures, it could present kind of a double edged sword, with a lack of food during the winter and an increase in metabolic demand because of the warmer water temperature.

And then there’s also summer temperatures. Summer is a time when here actually the temperatures are not as ideal, like it actually gets a little bit warm in the summer and so if those summer water temperatures started rising and we know there’s a relationship between the rise that we see in air temperature and a rise in water temperature so it’s pretty predictable. If we know the air temperatures are rising this much, we can predict that groundwater is going to rise. And for some of our streams there actually isn’t a whole lot of room temperature-wise to go up before trout are going to become stressed and so what exactly the projections are in terms of when that’s going to happen yet very.

Have any projections been made regarding climate change effects on the trout, invertebrates or the streams?

There was a study done by some folks at the Wisconsin DNR probably six or seven years ago now where they actually did some modeling for Wisconsin trout streams. Actually, I think they did it for all fish, but they included brown trout and brook trout and they did temperature projections. What they tried to look at was if air temperatures increase one degree three degrees or five degrees in the next 50 years. What’s going to happen? And what they found was that brown trout distributions are going to, I forget what the exact percentage is but let’s say 90 percent decline and the brook trout would be done with a three to five degree increase in air temperature. So it is one of those things where it doesn’t look very good.

Now what can we do about that?

We have to kind of pinpoint which streams have habitats that support a good diversity of aquatic invertebrates, that are shady and have good water quality.

Currently our habitat improvement practices remove most trees from the stream banks to slope and connect the flood plain. How do we shade the streams but also slope eroded banks? Are there steps or practices we can consider with regards to habitat that might help?

So I think one thing that you could look at is having heterogeneity or differences in habitat, so not necessarily having shade along the entire stream but having shaded areas with considerable depth that serve as a refuge throughout the stream. We call this a thermal refuge so that there is a spot where, especially those bigger trout on higher stress days, can go when they are feeling more stressed. The diversity on the banks is important because I think a lot of research has shown that having banks that have grasses and shrubs and aren’t bare, that’s actually good because then you have a diversity of invertebrates. You get more production of terrestrial invertebrates that can wash into the streams which is a good thing, although in the driftless area terrestrial invertebrates are a relativity small percentage of trout diets. Overall I think good water quality is an important thing, reducing runoff, and monitoring the watershed as a whole, all that stuff kind of plays a role.

What can the average angler do to help the trout or invertebrates?

I think go trout fishing, the general recreational activity of fishing does not have a profound negative impact on the majority of our streams. Generally speaking, I don’t think that there is a huge amount of pressure on most streams given the amount of fish we have. With good management, many of our streams have healthy populations of trout and so they can kind of handle the historical angling pressure. And one of the big things is just continuing to buy trout stamps, continuing to buy fishing licenses which contributes to the funding that agencies get. In our area, the more connected we are and the more you can create a connection to trout streams the better it is for the overall conservation of things. Even now I’ll meet people who’ve grown up here and they barely know this place has trout. This can’t be a good thing when, you know, they’re the ones who live here, they’ll be influencing policy makers on the size of frac sand mines we should allow. If they don’t understand that connection.

So I think in general for trout, fishing is actually a really good thing and keeps us engaged. It keeps us engaged and also I think sends a message to the state that this is where money needs to be going. They do surveys of anglers and when they’re allocating dollars for research and conservation and habitat management, they look at, where people are recreating. And so I think that fishing and engaging is a big one for sure.


  1. Lyons, J. , Stewart, J. S. and Mitro, M. (2010), Predicted effects of climate warming on the distribution of 50 stream fishes in Wisconsin, U.S.A.. Journal of Fish Biology, 77: 1867-1898. doi:1111/j.1095-8649.2010.02763.x




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