MIGRATION OF ADULT ATLANTIC SALMON (SALMO-SALAR) - THE EFFECTS OF ARTIFICIAL FRESHETS

The upstream migration of Atlantic salmon tagged with radio transmitte rs was analysed on a 6 km long stretch of the River Mandalselva (south ern Norway), where the residual flow was 3 m(3) s(-1). Over a period o f 40 days six artificial freshets were released. Two of the freshets l asted continuously for 48 hours and four of the freshers consisted of successive pulses of increased water discharge. There were significant differences in mean migration distance per hour between the freshet p eriod, the 11 hour post-freshet period and the residual flow period fo r three of the freshets. However, no clear relationship between increa sed water flow and stimulated salmon migration was found.