TEMPORAL VARIATION IN MICROHABITAT USE BY AGE-0 SMALLMOUTH BASS IN THE NORTH ANNA RIVER, VIRGINIA

Microhabitat use by age-0 smallmouth bass Micropterus dolomieu in the North Anna River was quantified from 10 snorkel surveys conducted betw een May and August in 1990 and 1991. Depth, mean velocity within the w ater column, substrate, and cover were quantified in 25 larval brood s ites, and the same variables (plus focal-point velocity) were quantifi ed at 634 points where dispersed individuals were located. Larvae in b roods occupied a wide variety of microhabitats, but after larvae dispe rsed from brood sites they primarily occupied low-velocity areas with large substrate or cover. During the first 4-6 weeks after dispersal, juveniles continued to use relatively deep, low-velocity microhabitats . Thereafter, juveniles occupied shallower microhabitats with greater focal-point velocities. Fish size was generally not related to microha bitat use within a sampling period, except during two periods when the re was a positive relationship between size and depth use. Microhabita t use of the age-0 cohort of smallmouth bass changed as these fish gre w, but the microhabitat use of an individual juvenile could not be pre dicted solely by the size of the individual.