Obligate Drift Feeding Behavior of Moapa Dace Moapa coriacea: a Drift Manipulation Experiment

Understanding ecological limitations on endangered desert fishes and ecosystems and how anthropogenic water withdrawals will affect them is essential to their conservation. To investigate potential feeding behavior limitations of endangered, drift-feeding Moapa dace (Moapa coriacea), we experimentally manipulated food availability (0, 34, 64, 100, and 200% of the natural drift level) and quantified their feeding attempts, success, and consumption rates. We found that Moapa dace are obligate drift feeders, selecting drift 40 times more frequently than benthos. They did not adaptively shift foraging modes from drift to benthic when drift was reduced experimentally. Drift feeding rate increased in response to increasing drift. Drift feeding attempts per 15 minutes was 8.8 higher at 100% and 16.0 higher at 200% of the natural drift level than at the 0% drift level. Drift feeding success only increased from the 0% to the 64% drift level and did not change in the 100% and 200% levels. No relationship between aggression and food availability or fish size was detected. Moapa dace may share an interspecific foraging association with sympatric White River springfish (Crenichthys baileyi). Maintaining in-stream flows and restoring habitat to provide abundant drifting macroinvertebrates would likely aid in Moapa dace recovery.