Diel onshore–offshore migrations in northern redbelly dace, Phoxinus eos (Cope), in relation to prey distribution in a small oligotrophic lake

Abstract

Northern redbelly dace, Phoxinus eos (Cope), exhibit diel onshore–offshore migrations in a small oligotrophic Quebec lake. The fish swim in shoals in the littoral zone during the day, migrate to the pelagic zone at sunset, where the shoals break up into single fish, and then go back to the littoral zone at sunrise. Dace eat mainly two cladocerans, Daphnia and Holopedium. Zooplankton sampling indicated that Daphnia were significantly more abundant in the pelagic zone than in the littoral zone, and Holopedium were rarely found in the littoral zone. Dace showed a significant preference for a dense cover habitat over a sparse cover habitat in the littoral zone during the day. Our results support the hypothesis that dace migrate to the pelagic zone at sunset to increase their feeding efficiency on zooplankton. The foraging benefits of remaining in the offshore zone may be offset by increased risk of predation by brook charr, Salvelinus fontinalis (Mitchill), during the daylight hours, thus resulting in diel onshore–offshore migrations.