Movement and Distribution of Smallmouth Bass in the Middle Snake River

Abstract

Listen

Translate article

The movement and distribution of smallmouth bass, Micropterus dolomieui, were studied in the Snake River, a large western river, prior to impoundment. A tag and recovery program was designed to assess interpool movement. Smallmouth bass were collected by angling and electrofishing. Primacord, a detonating fuse, was used to assess distribution during late fall and winter. Underwater observations were made with SCUBA apparatus. Bass behavior was studied in the laboratory and dealt principally with temperature effects, light intensity and substrate. Only 8% of the tagged fish recaptured were taken by anglers; the remaining 92% were taken by electrofishing. Ninety-nine (76%) of the recovered fish free at least 7 days were found in the same pool or defined location in which they were tagged, while 22 of the 31 fish recovered outside the pool in which they were marked had moved less than 1200 m (1,312 yds). A few moved several kilometers upstream or downstream from the release point. There was no significant seasonal variation in numbers of fish moving in different seasons, although there seemed to be slightly more movement in spring and less in summer than the mean movement. The distances moved at various seasons were not significantly different, nor was the seasonal direction of movement. A preference for broken rock substrate was indicated in the river by high fish densities over this type of substrate. Few smallmouth bass were found over a solid rock substrate, and none was observed over sand. In late fall, as water temperatures dropped below 15.5 C (60 F), smallmouth bass could not be located by electrofishing in water less than 2.3 m (8 ft) deep, but were found in still rocky pools at least 3.6 m (13 ft) deep by detonating primacord on the pool bottoms. The distribution of smallmouth bass within a pool changed during the 24-hour day. Smallmouth bass observed in early morning were all near the edge of the current. When the location of the edge of the current changed due to fluctuating water level, the bass shifted to the new position of current edge. In early morning no bass were observed more than a few meters from the edge of the current. Nocturnal positions of smallmouth bass were on or beneath a broken rock substrate in still water. When beneath the substrate bass faced toward an exit. No movement by smallmouth bass was observed in the river at night. In the laboratory smallmouth bass fed during the day and went on or beneath the substrate during darkness. This change in position took place at dusk. Some individuals appeared to defend night locations and rock substrate appeared preferable to sand. Fish came out from beneath the substrate at low light intensities in the morning. Activity decreased with temperature. Most of the fish remained beneath the substrate while temperatures were less than 6.7 C (44 F) and came from beneath the substrate when the water temperature reached 7.8 C (46 F).