A Review of Drift Foraging Models and Future Prospectus

Both food and space have been indentified as regulators of stream salmonid populations. In the early 1980’s research on these two factors took distinctly separate paths, developing into physical habitat modelling (e.g. Bovee 1982) and the origins of drift foraging-based models (Fausch 1984). More recently these paths have rejoined in the development of bioenergetics-based habitat selection and growth models that include both detailed physical habitat assessment and drift foraging success. The energetic component of these models are based largely on Hughes and Dill’s (1990) landmark drift-foraging model and the latest versions being implemented as both research and environmental assessment tools (Hayes et al. 2007; Railsback et al. 2009). I foresee rapid expansion in the application of energetics-based habitat models for drift-feeding fishes, although increased cost over traditional hydraulic-habitat modelling is a constraining influence.  However, considerable deficiencies in our understanding of drift foraging remain.  Recent tests have found quite large discrepancies between predicted and measured GREI (e.g. differing by a factor of 2), and predicting foraging costs is also challenging.  These deficiencies mean that fully quantitative predictions of GREI and NREI remain elusive which has rather serious consequences for accurate predictions of growth and carrying capacity.  Predicting habitat selection is more tractable because this simply requires relative estimates of NREI. The next generation of foraging models would benefit from research directed at prey detection, prey interception maneuvers, and the physiological and behavioral controls on temporal patterns of foraging effort and daily consumption.