Table 2. — Percentage dry weight dietary composition of subyearling coho salmon and steelhead sampled at 4-h intervals over a 24-h 



period, 13-14 July 1979, in Orwell Brook, N.Y. 



identical for the two species. Terrestrial prey were 

 most important in the diurnal diet of steelhead 

 (28.2-42.4%) whereas nocturnal feeding was al- 

 most exclusively on autochthonous prey 

 (92.7-95.6% ). Like coho salmon, peak consumption 

 of terrestrial invertebrates by steelhead occurred 

 from 1600 to 2000 h while peak consumption of 

 aquatic prey was from 2000 to 2400 h. Baetid, 

 caenid, and leptophlebiid mayfly nymphs along 

 with immature and adult chironomids were the 



only aquatic prey taxa which were well repre- 

 sented in the diet of steelhead during each 4-h 

 interval (Table 2). 



The two species exhibited diel differences in 

 feeding intensity (Figure 1). Coho salmon fry fed 

 heaviest from 2000 to 2400 h, while peak feeding 

 of steelhead trout fry occurred from 1600 to 2000 

 h. (The feeding intensity of steelhead fry also in- 

 creased substantially from 1200 to 1600 h.) In 

 general, the greatest variation in the amount of 



373 



