EFFECTS OF ANGLING ON POPULATION-STRUCTURE OF BROWN TROUT, SALMO-TRUTTA L, IN MOUNTAIN STREAMS OF NORTHERN SPAIN

Effects of angling exploitation on brown trout populations were assessed by comparing fished sections with close ones unfished for at least 20 years, in mountain streams of Asturias (Northern Spain). Both the fish size and age structure significantly differed among sections in the expected direction according to their exploitation status. The main effects were a significant decrease in age structure complexity (diversity), life span, and percent individuals above the legal limit size in the exploited stocks versus the unexploited ones. Trout above the minimum length limit for fishing (18 cm) averaged 19.47% of the fish caught in the unfished sections (sd = 4.01; n = 5), and 4.72% (sd = 3.46; n = 4) in those subjected to angling. Furthermore, fish older than 4 years represented 39.84% (sd = 8.53) and 1.19% (sd = 1.60) of the catch, respectively. Effects on recruitment (density of young fishes) and growth rates (length at age 1+ to 3+) were not absolutely consistent, though maximum values were associated with fished sections.