Havsöringens (Salmo trutta) lekvandring i Själsöån, Gotland.

Sammanfattning:

In this study, the sea trout (Salmo trutta) spawning migration was studied in the river Själsöån, Gotland, to assess the main external factors determining upstream migration and seasonal changes in fish parameters. Additionally population trends were studied by examination of old data. The most important external factors for upstream migration were the air pressure, air temperature and wind direction. No significant difference was found between when males and females migrated upstream. Larger females in better condition started migration earlier than the smaller females in poorer condition. Later arriving females stayed in the stream for a shorter period. Regarding changes over time, the results showed that the variation between years in number of spawners, female size and condition, and sex ratio was high but with no trends. The population appears to be stable.