RECOVERY OF YOUNG BROWN TROUT IN SOME ACIDIFIED STREAMS IN SOUTHWESTERN AND WESTERN NORWAY

摘要

Temporal changes in densities of young brown trout (Salmo trutta), mainly of age 0+, and in water quality (pH and alkalinity) were assessed by means of electrofishing in lake tributaries in three acidic, softwater watercourses in western and southwestern Norway; Gaular and Vikedal (1987-1999) and Bjerkreim (1988-1999). Approximately 74 sites were sampled each year. Most of the streams were acidic with mean annual pH levels between 5.1-5.9. Alkalinity and pH increased significantly in all three areas during the study period. Brown trout fry densities increased significantly during the period in Vikedal and Bjerkreim. Also in Gaular, the density of young brown trout has exhibited a positive trend in recent years. We suggest that the increase in the density of young brown trout is because the study areas have became less acidified during recent years due to reduction in sulphate deposition.