The summer diet of brook trout (Salvelinus fontinalis) in a South Island high‐country stream

Abstract

Abstract The diet of brook trout (Salvelinus fontinalis) living allopatrically and sympatrically with brown trout (Salmo trutta) in Dalgety Stream, South Canterbury, was examined during January 1985. Both adult (> 80 mm fork length, FL) and juvenile < 30 mm FL) allopatric brook trout fed predominantly on Deleatidium nymphs, caddis larvae, and chironomid larvae. Where brook trout coexisted with brown trout, adult brook trout fed mainly on Deleatidium nymphs, larvae of Olinga and Pycnocentrodes, and chironomid and empidid adults. Brown trout adults also fed predominantly on these species, although Pycnocentrodes larvae were rare. Chironomid larvae were the most important food items eaten by fry of both species. In terms of biomass, cased caddis larvae made up a large proportion of the material ingested owing to their heavy indigestible cases. Partitioning of food resources was not evident where brook and brown trout occurred sympatrically.