Habitatpreferens hos Anguilla anguilla: makrofyters påverkan på gulålars habitatval under dag och natt

Sammanfattning: Aquatic vegetation and different substrates can be important factors for fish habitat. The European eel (Anguilla anguilla) is threatened by habitat loss in freshwater systems during its life stage as a yellow eel. To conserve the species, restoration measures and increased knowledge about its preference for benthic habitats are needed. In this study, I examined how macrophytes with varying densities affected the habitat selection of A. anguilla yellow eels during day and at night. A laboratory experiment was conducted in three stream flumes containing sand and stone habitats, with an open passage where the eels (n = 17) could swim between them. The stone habitat was the same in all flumes, whereas the sand habitat had three macrophytes densities: 14, 7 and 0 m-2. The number of times the eel switched between the habitats, the time to the first habitat switch and the proportion of time spent in each habitat was noted. The result showed no significant effect of vegetation density on the number of habitat switches, the time to the first switch, or the proportion of time the eels spent in each habitat. There was no difference between night and day regarding the number of switches between the habitats. However, the proportion of time spent in the habitats differed between night and day; the eels spent more time in the stone habitat at night than during the day (Z = 2,707, n = 17, p = 0,038). The results suggests that yellow eels are active at night and may leave their resting habitat among the vegetation to search for food when it gets dark. Aquatic vegetation may be an important feature of yellow eel habitat, and to restore these environments, targeted restoration efforts and an increased understanding of macrophyte occurrence and substrate composition are needed.