DIEL AND DENSITY-RELATED CHANGES IN FOOD-CONSUMPTION AND PREY SELECTION BY BROOK CHARR IN A NEW-HAMPSHIRE STREAM

We report the results of a field study testing influences of both dens ity and changes over the diel cycle on food consumption and prey selec tion by brook charr, Salvelinus fontinalis. Charr density in replicate 35 m long sections of a New Hampshire stream was adjusted to either m edium or high levels (relative to natural densities). Diets of charr a nd the availability of drifting prey were then sampled every four hour s for 24 hours. There were no significant diel changes in the weight o f prey consumed by charr per four hours, though there was some indicat ion of reduced feeding at night. Charr fed selectively on different pr ey taxa, showing most preference for cased caddis larvae. Several spec ies of mayflies and stoneflies were selected more strongly during the day than at night. Charr fed selectively on larger prey during the day time but showed no size-selection at night. The density of chaff had n o significant effects on either their rate of food consumption or on s election for prey of different taxa or sizes.