Seasonal feeding selectivity of brown trout Salmo trutta in five groundwater-dominated streams

Abstract

Availability and selection of macroinvertebrate prey is important to explain temporal and spatial variation in growth among stream salmonids. However, few studies contain information to identify such relationships. Our objectives were to quantify drift and benthic macroinvertebrate prey availability and selection by brown trout on a seasonal basis in five streams across three years in southeastern Minnesota. Few taxa were dominant in diets and the environment with considerable variability in drifting and benthic prey within streams and seasons. Brown trout consistently selected only one or two taxa, and displayed neutral or negative selection for other taxa. In general, large-bodied, energy-rich benthic prey were selected over other more abundant aquatic macroinvertebrate taxa and drifting prey. Foraging patterns suggested a preference of benthic feeding. Electivity of benthos and drift varied spatially and temporally with a negative relationship between the total proportion of prey available and prey electivity. In general, seasonal growth and prey electivity were not related across all streams, but were positively related within two of five streams. Understanding seasonal and spatial relationships among growth, prey availability, and prey selection may aid future management of streams, as climate change is expected to alter physical conditions and biological communities of streams.

Keywords

• Brown trout
• driftless ecoregion
• seasonal diet
• prey selectivity
• groundwater-dominated streams