USE OF FIRST-ORDER TRIBUTARIES BY BROWN TROUT (SALMO TRUTTA) AS NURSERY HABITAT IN A CENTRAL WISCONSIN COLDWATER STREAM NETWORK

Abstract

Many studies have examined the importance of suitable in-stream habitat and flow regime to salmonid fishes. However, few studies have examined the use of small (< 5 L/s discharge) headwater streams within a larger stream network by trout. The purpose of this study was to evaluate the use of headwater streams by juvenile brown trout Salmo trutta in the Emmons Creek stream network in Wisconsin, USA, and to determine if abundance and body size of trout are related to habitat and food supply in these streams. Fishes in nine spring-fed first-order streams were sampled during a seven month period using a DC backpack electroshocker, identified, and measured for total length. Habitat and biological variables assessed included stream discharge, water velocity, sediment composition, abundance of cover items (woody debris and macrophytes), and benthic macroinvertebrate density. Monthly densities of YOY trout ranged from 0 to 1 per m2 and differed among streams. Regression analyses revealed negative relationships between fish density and discharge and positive association between fish density and % fine sediment among 1st-order streams in the spring (April and May) but not in the summer (July and August), reflecting the results of previous studies of the habitat preferences of trout in larger streams. There was divergence in mean fish length among 1st-order streams as the study period progressed, and in August mean YOY lengths by stream were negatively associated with density. My work demonstrates the viability of small first-order streams as nursery habitat for trout, and supports the inclusion of headwater streams in future conservation and stream restoration efforts.