WISCONSIN BASS MANAGEMENT PLAN

The smallmouth bass also occurs in all Wisconsin basins; its distribution has not changed substantially since the turn of the century, even though considerable transfer and stocking efforts have occurred over the years. Over 3,500 miles of stream contain smallmouth bass. The smallmouth is common in medium to large streams with abundant cover and shade and in large, deep (average depth > 9 m), clear lakes throughout Wisconsin, as well as in upper Green Bay of Lake Michigan and Chequamegon Bay of Lake Superior. In rivers, adults are present in moderate to swift currents associated with rocky substrate (>45%), while young-of-year occur in eddies along the banks and are associated with cover (e.g.,vegetation, rubble, banks, or other woody cover) because they generally avoid open water. In lakes, smallmouth bass are strongly associated with cover over rocky or sandy substrate; lakes over 20 feet deep, with rooted aquatic vegetation and clean, gravel shores with abundant cover provide optimum habitat. It often occurs near rock ledges and rocky bottoms, but may also be found along weedy shorelines. Smallmouth bass occur most consistently in shallow, near-shore waters (<15 feet deep) except during winter, when they generally remain in deep pools (rivers) or deeper areas of lakes. In rivers, smallmouth bass can migrate long distances seasonally, so habitat requirements vary spatially and temporally; unregulated rivers appear to be critical to smallmouth bass. Sedimentation is a major habitat factor in the viability of smallmouth bass populations.

Preferred bass spawning substrate is gravel, but spawning occurs on a variety of other materials, ranging from sand to plant fibers and roots or other exposed hard surfaces in otherwise soft muck or silt substrate. Water depth over nests averages about 2 feet. In waters containing both species, largemouth bass spawn earlier than smallmouth bass in shallower, protected spawning sites among emergent vegetation in quiet bays. Young bass remain in the nest for 6 to 15 days, after which they school together near the nest site for 10 to 28 days and then disperse throughout the shoreline. Predation is heavy during this period, so near-shore cover is important for survival of young bass.

Smallmouth bass spawn on rocky shoals, river shallows, or backwaters or move into tributaries to spawn. The species requires clean rock or gravel substrate for spawning. In lakes, smallmouth bass build nests first on the west and north shorelines, where waters warm faster and they are protected from prevailing winds. Nests are generally constructed on gravel and rubble, preferably beside a large obstructions such as a boulders or logs. Excessive siltation on fertilized eggs will result in parental abandonment and nest failure.

Clearly, littoral habitats with abundant cover (vegetation, rock, woody structure) and a variety of substrates, including rocky bottoms with very little deposition of fine sediments are crucial for both species. “Half-logs” have been used successfully to improve spawning cover for smallmouth bass in lakes lacking large woody structure such as downed trees (Hoff 1991).