DURATION OF SEA AND FRESH-WATER RESIDENCE OF ARCTIC CHAR (SALVELINUS-ALPINUS), FROM THE VARDNES RIVER IN NORTHERN NORWAY

Nine years of tagging experiments in the Vardnes River show that mean duration (+/- s.d.) of residence in the sea of the anadromous Arctic char (Salvelinus alpinus) was 47.7 +/- 15.6 days (annual means range 38-57 days). Females stayed in the sea for a significantly (P<0.0024) shorter period (mean 45.9 days) than the males (mean 48.8 days) and the females usually descended from freshwater later and returned earlier. Those fish that descended first usually had a prolonged period of sea residence. A pronounced annual variation in oceanic residence time was found. In general, the correlations between environmental parameters such as river and sea temperatures, and the duration of residence of the char in the sea, were low. However, the mean annual duration of residence in the sea was positively correlated with river temperatures in May and September (P<0.05). These results contrast with previously reported analyses of the duration of residence in the sea of anadromous brown trout (Salmo trutta) from the Vardnes River. Unlike the char, the residence period for trout in the sea was shorter in the coldest years during the study period. Our results suggest that char possess a considerable capability for growth in cold water.