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- ~~"~_.M"'.~"_'_-'____'~"_~_"._'__=_'__~_'_____"",,,,,~_""""",'-'",---."'-.......;.,..,~..-"""->-=.~~""""l"'.._""'~ 13 measured from the river bottom. Both measurements were made to the nearest 3 cm/sec using an electronic current meter. Fish depth, the distance of the fish from the stream bottom, was estimated by the diver to the nearest 5 cm. During the first - . three years of-collecting microhabitat data (including the first year of this study), the diver carried a calibrated rod to check his estimation of fish depth. When fish depth was greater than 2 m, the distance was measured with a calibrated rod or depth gauge. Water depth was measured during winter 1981 using a cali- brated rod (<5 m) or a calibrated line (>5 m). During summer 19H1 and winter 1982, a depth gauge was used to measure water depth. Thigmotaxis is defined as a taxis in which contact with a solid body is the directional factor. Fish are often not in con- tact with any solid body but they may remain in close proximity to one. In thi s study, the nearest thigmotactic surface wa s de- fined as the c\psest solid object or objects to the fish, which included the stream bottom, attached vegetation, submerged roots and branches, and boulders. The type of substrate was recorded as rock (>30 cm), rubble (8-30 em), gravel (0.3-8 cm), sil t (<0.3 cm), or other. Presence or absence of plant cover was recorded separately for each sub- s tra te type. / The level of overhead light reaching the fish was measured to,0.01% of full sunlight (1.076 X IuS lx) on a logarithmic scale uSlng a solar illuminance meter with an underwater probe during ~~ ~--:~..:tL.-.