Donald M. Baltz | Geology Reports

USGS1991

Seasonal changes in microhabitat selection by rainbow trout in a small stream

Shifts in microhabitat selection by rainbow trout Oncorhynchus mykiss were related to seasonal and ontogenetic factors in a small stream characterized by short riffles, small pools, and boulder substrate. Resource availability did not differ significantly between summer and November sampling dates for most variables related to water velocity, substrate, and cover, although depths were greater and temperatures were significantly lower in November. Ontogenetic shifts were found for total depth, focal elevation, mean water column velocity, focal velocity, surface velocity, and substrate, but not for relative depth or temperature. When microhabitat selection was adjusted for fish size, selection was significantly different between seasons, most notably for velocity. Ontogenetic shifts in microhabitat use by young-of-year rainbow trout were interrupted by cooling winter temperatures. These changes resulted in substantially different microhabitat requirements for all rainbow trout size-classes in different seasons.

Transactions of the American Fisheries Society↗

USGS1989

Spatial, seasonal and diel distribution of fishes in a California reservoir dominated by native fishes

During 21 months of sampling with various techniques, we captured 24 species of fish in Britton Reservoir. Nine species comprised over 96% of the number of fish captured and approximately 88% of the biomass. Five native non-game species accounted for over 77% of the catches. The native non-game fishes have maintained large populations in the reservoir despite continued introductions of non-native species. Two sources of non-native species exist. The first is the introduction of exotic species directly into the reservoir during fish-stocking programs. The second is the continuous movement of non-native fishes into the reservoir from large populations which reside in a major tributary of the reservoir. Factors responsible for the large number of native fishes are: management of the reservoir for hydroelectric generation; temperature regime; reservoir morphology. The fish community structure is stratified along two axes: upper basin/lower basin and inshore/offshore. Most of the 24 species were found inshore: 14 species were found offshore. Four of the native non-game fishes were most abundant in the upper basin: three introduced non-native fishes were most abundant in the lower basin of the reservoir. The offshore community was dynamic on a daily and seasonal basis.

California↗