Diurnal and seasonal resource partitioning in young brown trout (Salmo trutta), Arctic charr (Salvelinus alpinus) and Alpine bullhead (Cottus poecilopus) in a subalpine lake in southeastern Norway

Diurnal habitat and food segregation in young Arctic charr (Salvelinus alpinus), brown trout (Salmo trutta) and Alpine bullhead (Cottus poecilopus) were studied in Atnsjo, a lake in southeastern Norway. The mean lengths ± SD of the three species were 118 ± 20 mm (n = 872), 112 ± 14 mm (n = 109), and 66 ± 8 mm (n = 70), respectively. Epibenthic gillnet catches of all three species were much higher at night (21.00-05.00 GMT) than during the day (09.00―17.00 GMT). In general, there was segregation by depth zone between these three species, which were caught at night at mean depths of 17.3 ± 6.2 m, 7.9 ± 3.3 m, 13.6 ± 5.0 m, respectively. During the hours of darkness in spring and late summer, Alpine bullhead were more likely to be associated with the bottom than Arctic charr and brown trout. Artic charr fed almost exclusively on zooplankton, while brown trout and Alpine bullhead fed largely on insect larvae and Eurycercus lamellatus. Although selective differences are partly responsible for resource partitioning between the two salmonid species and Alpine bullhead, interactive segregation may also occur.