Process-based models of feeding and prey selection in larval fish

Feeding success is essential to larval fish survival. We present detailed mechanistic models of the foraging processes (prey encounter, approach, pursuit, and capture) in larval fish, where all parameters have explicit physical or biological meaning. The model is a unification of the processes believed to be important to prey selectivity and environmental regulation of feeding in fish. We include the sensitivity of prey to the hydrodynamic signal generated by approaching larval fish and a simple model of the potential loss of prey due to turbulence whereby prey is lost if it leaves the perceptive field during pursuit time. We parameterise the model for larval cod Gadus morhua L., a species for which data from numerous experimental and field studies are available. Model predictions are compared to observations of feeding rates under various conditions and appear to match estimated ingestion rates and prey selection in larval cod. Observed pursuit times of larvae are long and approach velocity slow enough to avoid an escape response from prey, but too short to avoid loss of prey at high turbulence levels. The pause-travel search mode is predicted to promote ingestion of larger prey than a cruising search mode. We use these models to evaluate temporal and spatial (vertical) diel feeding rates of larval cod across Georges Bank. Contrary to previous models, our model suggests that larval cod are food-limited only in deep waters along a 160 km transect of the bank at a prey concentration of 20 jig dry wt l(-1). The spatio-temporal fluctuation of turbulence (tidal cycle) and light (sun height) over the bank generates complex structure in the patterns of food intake of larval fish, with different patterns emerging for small and large larvae.