Abstract
The sea trout,Salmo trutta, from the Vardnes River generally stays in freshwater during winter. The results from 11 years of tagging experiments showed that the mean annual duration of the feeding migration in the sea was 68 ± 21 days (yearly means ranging between 54 and 88 days). A pronounced variation was found with size, sex and time of migration of the fish and between the different years. The males stayed for a shorter time in the sea (mean 66 days) than the females (mean 69 days) and they usually descended later and ascended earlier. Those fish that descended first stayed for the longest period in the sea. The mean annual duration of stay in the sea for first and second time migrants to the sea was positively correlated with the mean sea temperature in May (r2 > 0.5). A positive correlation was also found between the annual duration of stay in the sea for the sea trout above 33 cm and the mean temperature in the river in July (r2 > 0. 6). Prolonged mean yearly sea sojourn was generally correlated with higher sea temperatures. Water temperature-salinity effects are discussed.
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