Diel migration and spatial distribution of fish in a small stratified lake

Abstract

The diel migration and spatial distribution of fish were explored using six sequential 4-h sample gillnettings in the pelagic and littoral zones of Lake Verevi (Estonia, 12.6 ha, max. depth 11 m, hard-water, deoxygenated hypolimnion) in August 2001 and July 2002. Considering abundance, two-thirds of the total fish moved to the littoral zone. The biomass of fish was distributed evenly between the littoral and pelagic zones, where the topmost epilimnion accounted for 80–85% leaving 10–15% for the lower epilimnion in the pelagic zone. Just above the thermocline only some large specimens of perch Perca fluviatilis (L.) and roach Rutilus rutilus (L.) (1–5%) during the daytime were captured. No fish movements were recorded under the thermocline. Rudd Scardinius erythrophtalmus (L.) inhabited only the littoral zone; all the other species were captured in both zones. Juvenile perch stayed in the littoral zone, whereas juvenile roach was caught in both zones and was active over a 24-h period. Piscivores, perch and pike Esox lucius L., were inactive in the dark. Perch inhabited mostly the littoral zone and the duration of its activity increased with age. In summer-stratified Lake Verevi, sharp change in the values of oxygen in the metalimnion along with species interaction affected the spatial distribution of fish, while diel migration was light-dependent.