Spatial association of nest construction by brown trout Salmo trutta.

Spawning patterns in female brown trout Salmo trutta were examined by documenting the construction of nests in a small stream and later excavating them to recover progeny. The maternal provenance of nests was determined by genetic typing of embryos using microsatellite markers. Seventy-two nests, for which position and date of construction were known, were made by 59 individuals. Position and date of construction were known for a further 35 nests, comprising 11 Atlantic salmon Salmo salar nests and 24 nests which contained few or no progeny. Salmo trutta showed a behavioural preference for spawning near (≤ 1 m) prior nests; nests made by different individuals tended to accumulate in a spatial sequence that progressed upstream. The directionality of the association between prior and new nests suggests that later spawners use the residual depressions created by previous spawners as the first element of their own nests.