Experimental Data for Drift Foraging Models: What's New and What's Next

Estimating net energy intake (NEI) of is a key requirement in a new suite of models being developed to assess habitat quality for stream fish.  To estimate NEI, habitat quality models use a drift-foraging sub-model, typically based on Hughes and Dill’s (1990, CJFAS) well-known model.  The Hughes and Dill model estimates the energetic costs and benefits of a fish’s position in the stream based upon swimming costs and prey capture success. The model includes a number of unrealistic assumptions about prey detection and capture, and swimming costs, however, some of which might be addressed through lab or field experiments. Here we present the results of some recent experiments on the effects of water depth and velocity, and cold temperatures, on the foraging success of juvenile salmonids. We demonstrate that prey capture success is reduced by both faster velocities and colder temperatures, and that swimming costs appear to play a minor role in estimating NEI.  We also report on the effects of fish species and size. In general, much experimental work remains to be done in the area of drift foraging theory, however, and we will discuss ongoing research and future needs.