# Predicting and mitigating vulnerability of trout streams

Co-Principal Investigator: Bruce Vondracek.

Students: Jennifer Biederman, William French, and Jane Mazack.

Status: Project completed 30 June 2013.

Trout require streams with excellent water quality that are fed by groundwaters, which keep streams cold in summer but ice-free in winter. The trout sport-fishing industry is vulnerable to global climate changes that can increase stream temperatures, alter the cold-adapted aquatic insects that form trout diets, and affect trout reproduction. Increasing air temperatures are predicted to increase the maximum water temperatures during summer, but also are very likely to dramatically change winter thermal conditions in trout streams. Our objectives were to:

(1) investigate the role of stream bank vegetation and adjacent land use to minimize changes in stream temperatures in relation to climate change during summer;
(2) determine winter diets and growth of trout populations; and
(3) determine kinds, abundances, and timing of growth patterns of cold-adapted insects that are essential in winter diets of trout.

We examined 36 trout streams in the Driftless Area, using GIS coupled with habitat surveys for objective (1); seining and standard diet analysis techniques for objective (2); and rapid bioassessment protocols for objective (3). The project identified and rank the streams most vulnerable to increases in summer high temperatures, and will identify cold-adapted insects that are most critical to trout diets and growth during winter. Trout fishing annually provides more than $150 million dollars in direct expenditures to local economies in Minnesota and$654 million through the Driftless Region. With re-circulating dollars this represents more than one-billion dollars of economic stimulus to local economies. Our research enabled us to identify streams and food species that are most vulnerable to increasing temperatures, and translate scientific results into management strategies to protect and conserve this valuable industry.