DIEL AND SEASONAL-VARIATION IN FORAGING ACTIVITIES OF PUMPKINSEEDS INAN ONTARIO POND

We used time-lapse video with infrared illumination to record feeding activity of pumpkinseeds Lepomis gibbosus in two patches of littoral h abitat in a shallow, mesotrophic Ontario pond. Observations were made for 72 consecutive hours in each of eight ice-free months and include extensive, relatively nonintrusive field observations of pumpkinseed b ehavior at night. We tallied numbers of passes above the substrate and numbers of substrate strikes (at substrate or at vegetation). Variati on among months accounted for 40-50% of the total variation in rates o f daytime passing and substrate striking, which peaked in May and Sept ember. Among-day variation in daytime foraging activity within months was high, accounting for 50-57% of the total variance, and the varianc es we measured can be used to plan replication levels necessary to ach ieve adequate statistical power in future studies involving measuremen ts of daily ration or comparisons of exploitation rates in different h abitats. Simultaneous video monitoring at multiple sites allows one to factor out the day-to-day variance and provides a sensitive way to co mpare foraging variables in different sites or habitats. Although pump kinseeds are usually considered diurnal feeders, some foraging occurre d at night in each month. The median rate of fish passing at night was about half the median diurnal and crepuscular rates. Rates of substra te striking were much lower at night than during the day, but plankton ic feeding at night was higher, so that nocturnal striking rates on pl ankton plus substrate were more than 75% of the diurnal values. Noctur nal feeding by other visually feeding fishes is more important than we currently acknowledge, and needs to be incorporated into our thinking about interspecific competition and predation among littoral fishes.