Reproductive activity and summer residency patterns of smallmouth bass, Micropterus dolomieu, in a thermal discharge canal on Lake Erie

We evaluated the behavioral effects of the fluctuating temperature regime o n spawning phase smallmouth bass in a thermal discharge canal on Lake Erie. Fifty-three adult fish were angled from the discharge canal at the beginni ng of the 1994 spawning season and implanted with temperature sensing radio transmitters. The distribution of tagged fish in the discharge canal was c ontinuously monitored and recorded from late June to early October using th ree fixed monitoring stations. Seventeen of the tagged fish left the discha rge canal immediately following tagging and did not return. The remaining f ish, particularly males guarding nests, resided in the heated discharge dur ing the spawning period despite daily temperature fluctuations of up to 16 degrees C. Some females and non-nesting and post-nesting males moved in and out of the discharge canal throughout the study period. Fish numbers withi n the canal declined throughout the summer and, by early October, all tagge d bass had left the discharge. Water temperatures experienced by discharge residents closely matched station outflow values, as there was little diffe rence in temperature throughout the 550 m long discharge canal. On several occasions temperatures were near the published upper avoidance and toleranc es, but the nesting males did not leave the canal, until after the broods d ispersed.