Cold Enough for Ya? Remote Temperature Sensing Advancements for Trout Habitat Management

Streams supporting coldwater fish like trout often face challenges during the summer when high air and water temperatures cause thermal stress for fish. Areas of streams with warmer water temperatures can act as thermal barriers, limiting fish occupancy and passage. However, localized cold spots, known as thermal refugia, created by coldwater sources like seeps, springs, and headwater tributaries, offer potential protection against climate-related heat challenges. One problem for habitat managers is that traditional field-based methods for efficiently detecting and monitoring thermal refugia are limited.

This is where remote sensing technology, particularly the use of Uncrewed Aerial Systems (UAS, a.k.a. drones), comes into play. These tools enable the detection and mapping of thermal refugia, and provide valuable insights for habitat management and facilitating better-informed decisions.

Key Findings

• Recent advances in remote sensing technology offer improved methods for detecting and mapping coldwater sites in northern streams.
• Streams that support coldwater fish like trout face challenges during warmer months due to thermal stress, hindering fish occupancy and passage.
• Localized cold spots, known as thermal refugia, are created by sources such as seeps, springs, and headwater tributaries and offer important ecological benefits and potential climate resilience.
• Remote sensing, particularly using Unmanned Aerial Systems (UAS, a.k.a. drones), provides an efficient way to detect and map thermal refugia, enabling better-informed management.
• Scientists have developed and documented detailed technical methods for remote sensing operations, image acquisition, data processing, and resource analysis.

Photo Credit

Mark Nelson

True color image (left) showing main channel, tributary, and snow-covered shore of Au Sable River, Michigan, and thermal infrared (TIR) image at the same location (right), acquired simultaneously in March 2022. The TIR imagery displays groundwater dependent ecosystem (GDE) location (red color) that is warmer than ambient winter stream temperature (yellow color), corresponding to colder than ambient stream temperature during summer.

 

Suitability of streams for trout and other coldwater fish is limited by periods of peak thermal stress during warmer summer months, preventing occupancy and acting as thermal barriers to fish passage. Coldwater inputs like seeps, springs, and headwater tributaries can either moderate the overall peak temperature within stream systems or create localized cold spots that provide thermal refugia, a specific type of groundwater dependent ecosystem (GDE). These GDEs allow seemingly unsuitable stream reaches to support coldwater fish populations under current conditions and offer potential future climate resilience.

Traditional field-based transect sampling approaches are effective at monitoring average stream temperatures but cannot efficiently detect ecologically impactful GDEs that are small and scattered. Managers need better information on the number, location, size, and ecological benefits of GDEs. Remote sensing technologies can support monitoring and mapping of GDEs, but mission planning, image processing, and resource analysis techniques have not been sufficiently developed, standardized, and documented over a variety of diverse stream-groundwater conditions. 

Building upon research and relationships established under a Great Lakes Restoration Initiative project, a Northern Research Station scientist partnered with Trout Unlimited; the University of Minnesota; and the Forest Service’s Geospatial Technology and Applications Center, National Forest Systems Eastern Region, Huron-Manistee National Forest, and Pacific Northwest Research Station to implement a practical UAS-borne thermal sensor technique for detecting and mapping the presence of GDEs that provide thermal refugia for coldwater stream fish. In this project, scientists developed, tested, and documented workflows for:

1.  Remote sensing mission operations
2. Image acquisition and data processing
3. Resource analysis approaches, resulting in a detailed technical guide for conducing management-relevant monitoring.