MOVEMENTS AND HABITAT PREFERENCE OF ADULT RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) IN A NEW-ZEALAND MONTANE LAKE

Adult rainbow trout (Oncorhynchus mykiss) in Lake Coleridge were tagge d with ultrasonic transmitters in 1999, and tracked for up to a year t o determine movements, and spatial and temporal changes in habitat pre ference. Three types of movement were identified: wide-ranging coverin g much of the lake, localised within the littoral, and migratory towar ds river mouths before spawning. Maximum swimming speeds up to 2.27 km h(-1) were observed, and speeds of 0.5 km h(-1) over several hours we re recorded for two fish tracked in the limnetic zone. Adult rainbow t rout inhabited littoral areas through winter and spring, with most shi fting to a limnetic habitat in summer and early autumn. We suggest tha t the wide-ranging limnetic lifestyle is in response to opportunities for feeding on ichthyoplankton, notably larval bullies and galaxiids. Some individuals remained in littoral areas throughout the year, appar ently having adopted a benthic/nearshore feeding strategy. As winter a pproached several fish moved towards the mouths of inflowing streams, before undertaking spawning migrations.