Lake spawning brown trout. Long-run effects of acidification and different liming strategies on egg survival and recruitment in Store Hovvatn and Vegår, Aust-Agder.

Sammendrag

The study is based on long-run investigations of egg survival and recruitment to the populations of lake spawning brown trout in the limed lake Store Hovvatn and the limed lake Vegår. The combination of shallow spawning grounds and acidic runoff during winter was found to cause low egg survival in redds of trout in both lakes. Additions of limestone onto the spawning grounds were found to substantially increase the egg survival in both lakes. It is therefore concluded that this is a useful method for enhancing egg survival of lake spawning brown trout in acidified lakes. Catchment liming in 1999 most likely caused the observed temporal increase in egg survival in Store Hovvatn in 2001-2004 period. Thereafter, the egg survival declined, most likely due to the reduced effect of the catchment liming.