Selective predation on zooplankton by pelagic Arctic charr, Salvelinus alpinus, in six subarctic lakes

Selective predation by planktivore fish appears to be an important regulatory factor of zooplankton communities, potentially causing large changes in species composition and size distributions within populations. In this study, prey preferences and size-selective predation on zooplankton by Arctic charr were examined in six subarctic lakes with Arctic charr as the dominant pelagic fish species. Most of the lakes had a zooplankton community dominated by copepods (Cyclops scutifer and Eudiaptomus graciloides), but the pelagic charr evidently selected cladoceran species (Bythotrephes longimanus, Daphnia sp. and Bosmina sp.), likely because the copepods have a higher mobility and evasiveness than the cladocerans. Furthermore, a strong size selection was also revealed for both Bosmina sp. and Daphnia sp., as individual prey from Arctic charr stomachs were exclusively larger than individuals sampled in the environment. Additionally, visibility due to size, morphology and pigmentation (egg-carrying females) was also a major factor for the selection of zooplankton prey. In conclusion, Arctic charr was found to be highly selective on zooplankton both in respect to species composition and individual size of Bosmina sp. and Daphnia sp.