Zoological Studies

Microhabitat Use by Formosan Landlocked Salmon, Oncorhynchus masou formosanus

Eric Hsienshao Tsao, Yao-Sung Lin, Robert J. Behnke and Eric P. Bergersen (1998) Microhabitat requirements of the Formosan landlocked salmon (Oncorhynchus masou formosanus) were studied in four 85-m-long sections of the Chichiawan Stream. Underwater observations to locate the salmon, followed by measurements of physical habitat variables, were conducted along transects established at 5-m intervals. Available and occupied habitat units were compared to quantify water depth, current velocity, instream cover, and substrate type of suitable microhabitat. Data were pooled to represent salmon habitat use during 2 water temperature periods. Newly emerged fry extensively used habitats with nearly no current velocity and abundant instream cover. More than 50% of the salmon from 5 to 9 cm moved into deeper water having moderate current (0.1 to 0.86 m/sec) and less instream cover. Adult salmon used slower (less than 0.2 m/sec), shallower sites with abundant instream cover for resting, and fast velocity (0.6 to 1.1 m/sec), deeper sites with less instream cover for feeding. Spawning salmon preferred shallower waters (0.1 to 0.39 m), slower currents (0 to 0.3 m/sec), and small to moderate substrate sizes « 25.6 cm). Microhabitat selection by Formosan landlocked salmon is related to fish size, water temperature, and life history activities.