Anomalous spawning of smallmouth bass in Nebish Lake, Wisconsin: Implications for early spawning and over-winter survival

We observed that the smallmouth bass (Micropterus dolomieu) population in Nebish Lake, Wisconsin spawned twice-once during the traditional spring period and then again in summer, well beyond the typical spawning season for north-temperate lakes. We documented this anomalous spawning behavior and compared the characteristics of smallmouth bass nests built during the two distinct spawning seasons. Smallmouth bass built 463 nests (110.2 nests/km shoreline) as water temperature was rising toward 20°C. During the summer spawning period, 24 nests (5.7 nests/km shoreline) were constructed between 11 August and 29 August as water temperature was falling. Nests built in summer were significantly farther from shore, in deeper water, farther from cover, larger in diameter, and built by larger males than in the spring.