The energetic implications of the diel onshore-offshore migration by dace(Phoxinus eosxP. neogaeus) in a small oligotrophic lake

Abstract

We assessed the energetic implications of onshore-offshore migrations executed by dace (Phoxinus eos times P. neogaeus). We estimated growth, consumption, and activity rates for dace allowed to migrate and for dace restricted to the littoral zone during 45 days. We also estimated the growth and consumption rates of a permanent littoral resident, the pumpkinseed sunfish (Lepomis gibbosus) kept with migrating dace and compared these values with those obtained for sunfish kept with dace restricted to the littoral zone. Dace migrated from the littoral towards the pelagic zone at dusk and returned to the littoral zone at dawn. On average, 70% of the daily ration of dace was obtained during the migration. Consumption and activity rates of dace that executed diel migrations were twice those estimated for dace restricted to the littoral zone. Average growth of dace allowed to migrate was 0.38 g wet mass, but fish resticted to the littoral lost 0.36 g wet mass. Growth and consumption rates of sunfish were not affected by the confinement of dace in the littoral zone. The survival of dace in the presence of a littoral competitor and a pelagic predator appears closely linked to the energetic advantages associated to diel onshore-offshore migrations.