Feeding below the thermocline: implications for prey capture kinematics

Thermal stratification can significantly impact the distribution of species in aquatic systems. Organisms often travel between these thermoclines in order to locate prey and find optimal thermal condition. Since most aquatic animals are ectotherms, changes in ambient temperature can have immediate impacts on performance. We aimed to understand how prey capture kinematics change when bluegill sunfish ( Lepomis macrochirus ) are exposed to brief acute temperature changes that represent foraging bouts below the thermocline. To do this, we exposed bluegills to either 21°C (above thermocline) or 17°C (below thermocline) and fed them a cloud of defrosted brine shrimp. After digitizing high‐speed videography, we found that performance increased at the below thermocline temperature contrary to our prediction. During these feeding bouts, we noticed high variability in prey capture behaviors as the fish encountered the first prey item and subsequent prey items. In these successive feeding events, they demonstrated a remarkable amount of modulation in close succession. We conclude that acute exposure to the thermocline temperature tested here does not negatively impact prey capture. Furthermore, feeding in rapid succession could be a way to maximize prey captured while reducing energy for searching and capture.