Salmon and trout often use cold-water refuges when surrounding water temperatures are higher than their preferred water temperatures. The relatively cool areas may be small patches of cool water created by groundwater inputs or junctions with cold tributary streams. These “refuges” are described in detail at http://www.epa.gov/region10/pdf/water/torgersen_etal_2012_cold_water_refuges.pdf.
Remote sensing is useful to map spatial patterns of stream temperature, which helps to identify areas where conservation measures could preserve cold-water refuges. Graduate student Aimee Fullerton (University of Washington), USGS scientist Christian Torgersen, and colleagues examined water temperature profiles generated from airborne remote sensing in over 100 rivers across the Pacific Northwest. The majority of the aerial surveys were conducted with thermal infrared (IR) imaging (8–12 microns) using a Thermovision 1000 sensor (FLIR Systems), which is a scanning array thermal imager with internal calibration. Torgersen and colleagues compared observed patterns of river temperatures to theoretical models and examined associations between thermal profile types and physical geographical features, such as climate, topography, geomorphology, and hydrology. Fullerton presented preliminary results at the U.S. Regional Association of the International Association for Landscape Ecology annual meeting on April 14–18, 2013, in Austin, Texas.