Validation of an Instream Flow Recommendation Using Larval Fish Diets

The purpose of this study was to test the Flow-Pulse Feeding theory and Drift-Feeding theory.  Objectives were to quantify gut fullness and occurrence of food items consumed among larval fishes taken between flow tiers and between larval fishes taken during the day in slack water and those taken during the night in the drift.  During a one year period of observation among four sites and two rivers, mesolarval fishes of obligate riverine taxa had greater gut fullness following a 1 per season flow event than those taken following other flow event. Gut fullness consumed by metalarvae were independent of flow.  Among larval fish collectively and among taxa, gut fullness was greater during the day for fishes taken in slackwater habitat than those taken at night from swift water habitats.  Drift-feeding theory likely is not a mechanism to explain larval drift at night, and the value of flow pulses to larval fish feeding and subsequent recruitment was not consistent among larval stages. Nevertheless, this study begins establishing a process to quantify the value of flow tiers relevant to the stream fish community.