brook trout
Coldwater fish, such as Wisconsin’s native brook trout, are very sensitive to changes in water temperature and other environmental conditions and may be important ecological indicators for climate change. In addition, native coldwater fish are an integral part of Wisconsin’s natural legacy, brook trout in net and coldwater fisheries are a core part of our culture and identity. Anglers make a significant contribution to the local and state economies in pursuit of their passion. In the face of changing climate conditions it is important to assess the potential impacts to coldwater fish and fisheries and implement adaptive management plans to ameliorate climate change impacts on Wisconsin’s coldwater streams and inland lakes and their fisheries.

The purpose of the Coldwater Fish & Fisheries Working Group is to identify the potential impacts of climate change on coldwater fish and fisheries in Wisconsin streams and inland lakes and to develop management adaptation strategies in response to climate change impacts. The Group will make use of existing information and propose new research where necessary to advance science-based management of coldwater fish and fisheries impacted by changes in climate.

Potential Risks

brook trout in net

Male Brook Trout
Photo by Matthew G. Mitro

The Coldwater Fish & Fisheries Working Group is in the initial stages of investigating the potential risks of climate change to coldwater fish and fisheries in Wisconsin. In general, the primary risks concern changes in water temperature and stream flow that may be attributable to changes in air temperature and precipitation.

Coldwater fish have specific thermal requirements and typically thrive in streams in which the mean summer (June-August) daily water temperature does not exceed 22°C. Questions remain, however, about how water temperature and stream flow will change in response to changes in air temperature and precipitation associated with climate change.

Potential impacts of climate change on coldwater fish will be mediated through changes in thermal habitat and stream base flow, as well as changes in stream geomorphology, groundwater recharge and input, water quality (nutrients, sediments, etc.), and other habitat variables. The impacts on coldwater fish may include changes in life history patterns, distribution, and community structure.

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Vulnerabilities

elk creek

Elk Creek
Photo by Matthew G. Mitro

The science is not yet conclusive and requires more investigation to identify the vulnerabilities of stream fish populations to climate change impacts. However, we expect vulnerabilities to occur in streams supporting coldwater fishes such as trout, which are generally intolerant to habitat degradation.

Coldwater streams are not distributed uniformly across Wisconsin. Streams that will be especially vulnerable to climate change impacts will also vary geographically across Wisconsin and within regions depending on the condition of individual streams. Streams in undisturbed watersheds with sufficient groundwater input may be well buffered to climate change impacts. Streams in urbanized watersheds or flowing through agricultural areas exhibiting severe erosion may be more vulnerable to climate change impacts.

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Data Needs

Data needs to address the identification of risks, vulnerabilities, and adaptation strategies are many and varied:

scientists walking in the river surveying elk creek

Photo by Matthew G. Mitro

  • Climate change predictions for Wisconsin (air temperature and precipitation)
  • Hydrologic models linking changes in air temperature and precipitation to changes in water temperature and groundwater input to streams
  • Watershed-scale habitat data (response to climate change and influence on streams and fishes)
  • Reach-scale habitat data (response to climate change and influence on streams and fishes)
  • Fish and habitat temporal trend data

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Adaptation Strategies

brown trout

Brown Trout
Photo by Matthew G. Mitro

The Wisconsin Department of Natural Resources currently manages coldwater streams by allocating resources based on the stream quality. For example, “wild” trout are stocked in streams that support survival of trout from year to year but limit reproduction and recruitment. Trout stamp revenues are used for habitat restoration on degraded streams. However, within these trout management strategies there is room for adjustments to create adaptation strategies to address climate change impacts.

Questions that remain include identifying those adaptation strategies that will best protect and enhance coldwater resources confronted by climate change. Such adaptation strategies may include the following:


Consider triage

A triage approach to the management of coldwater streams may involve classifying streams based on their potential to withstand climate change impacts. Our best, most resilient coldwater streams may be protected from habitat degradation. We may cease to allocate scarce resources to our marginal and least resilient coldwater streams. For those coldwater streams in between, we may allocate habitat restoration money or stocking quotas to those streams most likely to realize benefits in the face of changing climate.

brook trout tail being measured

Tail of Brook Trout
Photo by Matthew G. Mitro

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Plan for extreme events

Many models suggest that a changing climate may entail an increase in extreme weather events, such as the extreme precipitation and flooding events witnessed in Wisconsin in June 2008 and August 2007. If large-scale flooding events may become more common, we may need to rethink how we restore degraded streams in order to best withstand extreme and damaging weather events. The flooding in June 2008 and August 2007 has already given insight into how different habitat restoration techniques fare in extreme precipitation events.

Create and enhance refugia from high water temperatures

scientists walking in the river surveying timber stream

Photo by Matthew G. Mitro

In streams that may show resilience to climate change impacts, stream habitat may be managed to create and enhance refugia from high water temperatures. For example, stream channels can be narrowed and deepened, overhead cover can be added, and deep pools can be created to provide coldwater refugia in those streams receiving sufficient groundwater input. Riparian areas can also be managed to provide shading by tall grasses or trees.


Recognize the importance of land management in the watershed

Research has shown the importance of sound land management practices in a watershed to the quality of coldwater streams. Best management practices such as conservation tillage approaches to agriculture and the enrollment of environmentally sensitive land into the Conservation Reserve Program can be used to protect the biological integrity of coldwater streams and enhance their resiliency to climate change impacts.

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Contact

Please contact Matthew Mitro if you have any comments or concerns regarding Wisconsin's coldwater fisheries and the changing climate.