Wisconsin Public Television WCCI Matthew Mitro, Response of Wisconsin's Cold Water Fish to Climate Change Lecture 286: March 26, 2009  cc >> Our first speaker tonight is Matthew Mitro. And Matthew Mitro is a cold water fisheries research scientist for the Wisconsin Department of Natural Resources. He has worked on statewide trout stream research since 2003. Prior to coming to Wisconsin he was a population ecologist at the United States Environmental Protection Agency's Atlantic Ecology Division in Rhode Island and a stock assessment biologist for the Atlantic State Marine Fishery Commission in Rhode Island. Matthew received a PhD in fisheries at Montana State University where he studied rainbow trout recruitment. Matthew also received a masters in statistics at Montana State, a masters in fisheries at the University of Vermont and a bachelors in biology at Colgate University. So I'd like to welcome our first speaker. Thank you. >> Thank you Michael. So this evening I'm going to be talking about response of cold water fish in Wisconsin to potential changes in climate. 

Anybody who's ever gone swimming in Lake Superior in the summertime knows what cold water feels like. Cold water lakes, cold water ponds, cold water streams remain relatively cool during the summertime even when temperatures get hot. And by cool I mean temperatures in these water bodies remain maybe less than 70-degrees Fahrenheit or so, and oftentimes much cooler than that. For this presentation I'm going to focus on the cold water streams in Wisconsin. This here is a picture of a cold water stream located right here in Dane County, Mount Vernon Creek. Mount Vernon Creek, like many other cold water streams in the state are heavily influenced by the input of cold groundwater which tends to buffer these streams to changes in air temperature and helps them remain cool during the summer. Fish are ectotherms. Fish exchange heat with the environment around them and the body temperature of fish tends to be about the same as the water temperature around them. Temperature affects fish, it affects their biochemical and physiological processes in fish. And fish consequently have adapted to different temperature regimes such as they can function efficiently in these environments. 

So because of this we can say that some fish that have adapted to live in warmer water bodies we tend to refer to warm water fish. And those that have adapted to colder water we can refer to as cold water fish. This figure shows in a little more detail what it exactly means to be a warm water versus a cold water fish. But to begin with, fish are really amazing creatures in that they've adapted to live in some fairly extreme water environments across the globe. On the cold end of the spectrum, you have fish in the Antarctic that live in waters where the temperatures throughout the life of the fish never exceed 0-degrees Celsius. On the other hand, you have fish that live in warmer water environments. For example, fish that occur in lakes in eastern Africa. The water temperatures there are often up near 40-degrees Fahrenheit which is over, or 40-degrees Celsius which is over 100-degrees Fahrenheit. Here in Wisconsin we're in more of a temperate environment, seasonal environment, so we experience temperatures across the range. At this time of year, or in the winter rather, temperatures in all water bodies in the state tend to be very cold. 

But in the summertime as air temperatures increase, different bodies of water, temperature in different bodies of water increase to various degrees. The brown trout in this figure is one of the cold water fish in Wisconsin streams. Brown trout are fall spawners; they lay their eggs in the streams in the fall and their eggs incubate during the winter at colder temperatures. Brown trout then have a preferred feeding range which may range from about 5 to about 19-degrees Celsius or so. And within that preferred feeding range there is a range of temperatures in which growth is optimized. Now as temperatures rise towards 20-degrees Celsius or higher, the environment is a little bit warmer than these fish prefer and they start to become stressed. As water temperatures rise even higher, up to 25-degrees Celsius or more, the environment then becomes lethal for these cold water fish such as brown trout. But warm water fish such as carp, up at the top of this figure, those temperatures that are lethal for brown trout are actually optimal for carp. Which we would then refer to as warm water fish. So when dealing with, as pertains to fish and streams in Wisconsin there are two particular fish that are of major importance, particularly to recreational anglers in the state, one of the them is a brook trout. 

This is the only native -- to streams in Wisconsin. And this figure, the green shaded area show the native distribution of brook trout in North America. And you can see that Wisconsin is sort of near the western and southern edge of its native range. Where the brook trout does occur further south in Wisconsin it tends to be in higher elevation areas such as in the Appalachian Mountains. Brook trout have also been introduced to other parts of the country, the lower peninsula of Michigan and many of the western states, and they've become naturalized in those environments. The other trout or fish species that's of importance in Wisconsin cold water streams is the brown trout. Brown trout are not native to Wisconsin. They originally came from Europe. They were brought here over a century ago. And they have been introduced and become naturalized in many streams and lakes throughout North America. 

So Wisconsin is a very important state in terms of cold water fisheries. We do have cold water trout streams located throughout the state. This is a figure that shows streams that the Wisconsin Department of Natural Resources manages for trout. These are streams that we've been in over the years, we've surveyed these streams. We have found trout and managed these streams to continue to support trout fisheries. There are over 44,000 stream miles throughout the state. Over 10,000 of these are classified as trout streams. We have further classified those waters based on the quality of trout fisheries that, or quality of trout populations that you'll find in these streams. Our class 1 streams, shown in red in this figure, are the best of our streams. These are the streams that support growth and survival of trout from year-to-year and also, and importantly, they support natural reproduction of trout such that these fish populations are self-sustaining and provide essentially self-sustaining fisheries. 

So we don't require supplementing these populations at all. The other streams, the class 2 streams, shown in blue and the class 3 streams in green, are streams that may be somewhat degraded, they do support trout growth, sometimes trout survival from year-to-year. Generally, they don't support natural reproduction. So these streams require supplementing by stocking fish in these streams to maintain adequate fisheries. And we also spend money that we raise through the sale of trout stamps to rehabilitate habitat in these streams. I'll step back a second. One other thing I wanted to add is that recreational trout fishing is a rather important part of the economy of Wisconsin. About a year ago the Trout Unlimited commissioned a economic impact report for the driftless area of Wisconsin. This is in the south western part of the state in Wisconsin and also across the border in Minnesota, Iowa and Illinois. And the report found that recreational anglers in the driftless area contribute over a million dollars annually to the regional economy. 

So recreational fishing for trout is an important part of the Wisconsin economy. Now back to climate change. You've heard a lot in this series about potential changes in climate in Wisconsin and when thinking about climate change in trout, a couple important questions include how do changes in the climate affect changes in the stream environment? And then how do changes in the stream environment may be attributable to changes in climate? How do they affect changes in trout condition, trout abundance or trout distribution? Now the University of Wisconsin Center for Climatic Research has been working recently on scaling down global climate models to get better, more region-specific predictions as to how climate may change in Wisconsin, in particular. What we found or what we've heard from the researchers at the Center for Climatic Research to date from the models they've worked on to date is that as far as temperature is concerned in climate change in Wisconsin, we may expect to see significant warming in all months of the year, particularly higher low temperatures. We may also expect to see more extreme heat, days in which the temperature exceeds 90-degrees Fahrenheit. And also less extreme cold, days in which temperatures are less than 0-degrees Fahrenheit. And then for precipitation, their models are predicting that we may see greater total precipitation throughout the state, primarily in the winter and spring. And we may also see more heavy precipitation events and fewer light precipitation events. So from here I'm going to discuss first temperature implications of climate change and then precipitation. Now we have a pretty good idea how temperature affects individual fish and in our case here, individual trout. 

Temperature is an important factor that affects metabolism and consumption of trout which are two important components of growth. And we do know that if temperature is increased above what is considered the optimum for growth, this can result in reduced maximum consumption rates, increased metabolic rates and then consequently decreased growth.  Moving on from what climate change may do to individual fish we then, of course, ask the question how does this translate to effects at the population level? We don't know quite as much about how changes in climate may affect the population level of fish, as opposed to individuals, but there has been some work that has been done. This is one study that came out a couple years ago in the proceedings of the National Academy of Sciences on mechanisms for climate induced mortalities on fish populations in whole lake experiments. And they did this study with juvenile rainbow trout. And in this controlled study they found that increased metabolism at higher temperatures resulted in fish actually trying to compensate for that by increasing their consumption rates in order to maintain their growth rates. And by doing this, by over-compensating for consumption, they then found that these fish were, that their greater feeding rates would put them more at risk, particularly being vulnerable to predators. And this resulted in a reduction of the survival of about 50% in this case. Back here in Wisconsin we've been working on, one of the things we've worked on recently was setting up thermal tolerance curves for brook trout and brown trout. In order to look at how changes in temperature may affect the distribution of populations of these -- in Wisconsin and Michigan. 

This is a project I worked on with Kevin Wehrly and Li Wang from the Michigan DNR using data from streams throughout Wisconsin and Michigan. And basically what I wanted to show out of this figure was that whether you're looking at various forms of, or various summaries of temperature, whether it is a daily mean or daily maximum temperature, at shorter exposure periods, as you're towards the bottom of this figure, these fish can tolerate somewhat sharp increases in temperature up to 24, 25, 26-degrees or so. But only for short time periods. As the exposure period increases from one to three to seven days or so, there's a very rapid decline in the temperature that these fish can tolerate. Such that if we were to see increases in stream temperature attributable to changes in climate or for whatever reason, if the exposure period to those temperatures were to increase beyond a day or two then it could start to limit the distribution or the suitability of these streams for fish for brook trout or brown trout. Another project that we've also worked on recently takes the issue of fish distribution an important step further. This is a project I worked on with John Lyons, who will be speaking next, and Janice Stuart from the USGS in Middleton. And the idea behind this project was to use readily available data for watersheds throughout the state using geographic information system data layers for land cover, geology and such variables. And setting up models to then predict, based on this watershed habitat and climate inputs, which would be the stream temperatures that we would encounter in any stream temperature in that watershed and then what would be the suitability of those streams with different fish species. Would the fish species such as brook trout or brown trout be present or absent. 

Two of the models we looked at, the first one at the top there, the inputs were landscape variables and climate data and we used these models to predict stream temperature. And in another model used again the landscape and climate data as well as predicted stream temperatures in stream flow to then predict whether a fish species was present or absent. So what we got out of this was a present day snapshot of which stream segments throughout the state were suitable for a particular fish species versus unsuitable. For brook trout on the left we found over 17,900-kilometers of streams, shown here in blue, which were predicted by the models to be suitable for brook trout. And brown trout on the right there. And it matches up with actual observations of these species of fish. We found out that the predictions were quite good in showing where these fish occur and where they don't occur in the state. Now given that some of the input variables to these models included climate variables such as air temperature, the next logical step might be to consider how would changes in these climate input variables affect the distribution of fish. It's not exactly what these models were designed for but we thought it would be interesting to look at these what-if scenarios. And for example, what if air temperature and stream temperature increased by 1-degree, by 3-degrees, by 5-degrees or so, how might we expect the distribution of these fish species to change in the state? I'm going to show you what those figures look like and I'll preface it by saying we think this will probably be considered a worse-case scenario. 

We don't believe that, for example, if air temperature were to increase across the state of Wisconsin that stream temperature would increase uniformly in all streams, for example. There are many reasons to believe that different streams would be buffered to different extents to changes in air temperature. And I'll get into that a bit when I talk about precipitation. So in this model if we were to increase temperature by 1-degree Celsius we found a significant loss in the number of streams that had been previously predicted to have brook trout present, losing 73% of them. And those are now changed to the pink color. Brown trout, however, tend to be a little bit more tolerant to changes in temperature or to increases in temperature than brook trout, and in fact might increase in distribution. Here's a model showing a 28% increase. So some of the streams that are no longer suitable for brook trout, now suitable for brown trout. We were to continue or what-if scenarios to 3-degrees Celsius we then see an almost complete loss of brook trout waters and now a significant loss of brown trout waters. And then finally 5-degrees model will predict none of the waters will be suitable for brook trout and almost none of the waters suitable for brown trout. 

But what I think we should just get out of this modeling exercise though is that stream temperature is very important for trout and very important in identifying their distributions throughout the state. But again there are reasons to believe that many of these streams may be buffered to different extents to changes in temperature. Another thing to consider is what factors influence stream temperatures. And in those models looking at landscape level variables, things like groundwater input, we used a rather coarse measure of groundwater input in these models, was important. Land cover was important, as well. If you have urbanization in the watershed, urbanization results in impervious surfaces. You get precipitation that tends to runoff and leave the watershed quickly rather than infiltrating into the ground and recharging groundwater. There are also other important stream reach variables which we did not consider in these models because we don't have that data for every stream reach in the state. But as an example some of our degraded streams tend to become wider and shallower over time. And those tend to warm up faster when air temperature warms up. 

Versus streams that are in much better condition and may be narrower and deeper and the water in those cases is more resistant to temperature change. So back to the predictions from the UW Center for Climate Research on precipitation they predicted general increases of precipitation in the state of Wisconsin primarily in winter and spring and more heavy precipitation events. This is where the good news, if there can be any good news for climate change, comes in. In that our cold water streams are basically cold water streams because of the influence of groundwater. If we do get more precipitation, it's believed that we will get more infiltration, better recharge in our groundwater and this can benefit streams by increasing stream flow. If you increase stream flow, you increase the volume of water in the stream. It will take more exposure to high temperatures to increase the temperature of that body of water. So there will be a little better buffer to changes in air temperature. About two years ago we started another study where we set up some long-term trout monitoring sites in the driftless area of Wisconsin. In which we wanted to look at changes in trout populations over time and changes in stream flow over time, as well. 

We put out our continuous water level monitors in these streams in early summer 2007. Every hour these monitors would make a pressure reading and from that we can get an estimate of the level of stream flow in an area. In the first two years of the study we actually captured two heavy extreme precipitation events. Some of the type of events that climatologists are predicting we might see more of in the future. Looking at a figure like this, of course the thing that probably jumps out to you first are these two flash floods that occurred. The one, the August 2007 flood in Wisconsin, and then the June 2008. But when we started this study it wasn't particularly to catch these large scale events but more to look at changes in base flow. And what we did find, for example in Timber Coulee here, if you look at the base flow prior to the August 2007 flood, after that flooding event, base flow in the stream had increased by about 12% to 13%. And then after the next flooding event in June 2008, base flow increase another 12%. So even though these precipitation events were extreme, large volumes of water moved through these watersheds very fast, we did apparently get a lot of infiltration into the groundwater and a bump up in stream flows in these areas. 

This is one more figure for a different stream, Plum Creek, also in the driftless area of Wisconsin. Again the stream received a lot of rain during these precipitation events as well. But the changes in the water level were quite different from Timber Coulee. Just kind of showing that in different watersheds precipitation events are going to affect changes in stream flow differently. Now I do want to comment a bit about these extreme precipitation events that have occurred. While they have been quite damaging to a lot of property along streams, areas that have been flooded, we've seen a lot of damage to roads throughout the driftless area, it turns out these extreme precipitation events are not quite as hard on the trout. We do see in some areas, this is a picture of the I believe the Sugar Creek. Some of these streams do get, when these high volumes of water move through very quickly, a higher gradient stream like this, the force of the water does do a lot of, affect a lot of change on the stream. It cleans out a lot of sediment throughout the stream, which of course is good for trout. It opens up a lot of gravel substrate which is important for spawning. 

But it can shift around these stones. And towards the back of this picture here on the stream you can also see damage to the stream bank. That becomes important to us as fish managers when we go out and try to restore streams. The next stream here is Big Spring Creek down in Iowa and Grant County. In this stream it also received, from what I've heard from other regional fish managers, probably the greatest flooding event in the past 30 years. There was a bridge, hard to see in this picture in the background there, that got completely washed out. And down in the lower right corner here I've shown a section of the stream that was about a mile downstream that had been worked on a couple years ago in which we put in what are called -- structures. These are essentially creating an artificial undercut bank. And if you're looking at that picture and a flooding event had not occurred and the structure had been intact you wouldn't be able to see it. These structures, you can probably see the wood board along the bank there, would have been covered by those big boulders. 

The water had completely washed these out. So that's something to keep in mind when we're going out trying to work on these streams to improve them for trout. If we're going to see large scale events that are going to wash out the work that we do, that might make us want to rethink what kind of habitat restoration we're doing in different parts of the stream. Other streams, here Timber Coulee again, as you get further down into the stream valley, somewhat lower gradient, the force of the water coming through from these large scale precipitation events is not quite as strong, you don't see quite as much damage as we see in more upstream areas. But Timber Coulee had also been worked on extreme habitat restoration. In this case, many of the stream banks had been sloped back to open up the stream channel so that when you get these large volumes of water moving down the stream channel, the water can leave the channel and go out into the floodplain. And that kind of dissipates a lot of the energy. And the case of Timber Coulee we didn't see any significant damage to any of the stream structures or stream restoration work that had been done on this particular stream. One last point I wanted to make about extreme precipitation events. If they do occur at the wrong time of the year, you can have a significant impact on the production of a new year class. 

Again, brown trout and brook trout are fall spawners. These eggs incubate in streams over winter. Around this time of the year these fish are emerging from the reds where the eggs were laid. And these fish are very small. They are 15 to 20 millimeters in length. You walk along the stream banks you may see some of these fish swimming around in the slack water near the stream channel or any of the sides of the stream channel. But if you get any significant flooding events at this time of the year, these little fish don't have a chance. They're going to get washed out of the system. And it's possible you can see a poor year class production in those years. So if this extreme precipitation events happen to occur at this time of year when these fish are most vulnerable, then we can see effects on recruitment to these populations. 

One year may not mean the end of a particular population but if it happens on too regular of a basis you might see population level effects. The precipitation events that did occur in the driftless area in the past couple of years did knock down younger year production numbers, but not to a level that it would have any impact on the population as a whole. So I'll finish up by discussing a few adaptation strategies for climate change. The first one I want to mention is considering the idea of triage. If we're going to see changes in climate, changes in temperature, changes in precipitation which may affect changes in our streams, we may want to identify the best trout streams and make sure we're protecting those ones that are going to be most likely to persist in the changing climate scenario. And then on the other end of the spectrum our most marginal trout streams. Those are the ones that we might want to set aside and not expend valuable resources on them. And so the ones in the middle we may want to devote our trout stamp dollars that we use to habitat restoration towards to rehabilitating streams in which we're likely to realize the benefits of habitat restoration, should climate change. Again preparing for extreme events. This is another stream that we've monitored, Mormon Coulee Creek. 

It's a highly entrenched stream. We saw the very extreme peaks in water flow during these flooding events. We want to make sure that if we're doing any restoration of streams like this we're not putting structures into the stream that are just going to get washed out should these flooding events happen again. But rather work on opening up these stream channels to the floodplain so that these floodwaters can be better dissipated and not exacting a lot of damage on these streams. We also want to make sure we can manage for, pay attention to managing for refugia from higher temperatures. Again, degraded streams tend to become wider and shallower. Those warm up faster. If we're going to restore those, we want to make sure we're narrowing these stream channels, and deepening them so that they're better buffered to changes in air temperature. In the upper right corner an example of a stream in which we've created artificial undercut bank. Again shaded cover for fish making sure we're using those in streams that may be at lower gradient sections where we're not going to see damaging floods ripping them apart. 

And then in some parts of the state we might want to manage for shading in riparian areas to protect streams from solar input. And then finally it's also going to important to make sure we protect groundwater and promote land conservation and conservation tillage methods in agricultural areas for improving groundwater recharge. Now there have been a study in Wisconsin that has looked at the effect of keeping some of our environmental essential agricultural land enrolled in the conservation reserve program. So essentially taking these environmentally sensitive lands out of agricultural production. And what we've shown that has done is actually vastly improved groundwater infiltration in those watersheds and has really benefited trout streams in those particular watersheds. So to summarize climate change in cold water fish such as trout. If we do see warming stream temperatures, this could potentially limit trout distribution. If we see increases in precipitation, we may have the benefit of improving base flow and this may buffer streams from the effects of any changes in air temperature. On the other hand, if these predictions of increased precipitation are wrong and we actually encounter a drought scenario, then it switches to the other end of the spectrum, droughts would actually exacerbate air temperature effects on cold water streams and trout. And then finally, it's going to be important for stream managers to rethink stream habitat and watershed habitat management in terms of paying more attention to adaptation strategies that can help our trout streams be a better buffer to changes that may have resulted from climate. 

That's what I have, and if there's anytime for questions I'd be happy to try to answer a few. [APPLAUSE]