The sea trout were tagged in the rivers, and included both immature and mature fish. Most were captured by rod fishing and tagged and released the same day. The great majority of fish were tagged in the spring prior to their annual sea migration, although a few were tagged at their spawning grounds in the autumn. Most of the DSTs were attached externally using a modified Carlin method although, in a few instances, the DSTs were implanted into the peritoneal cavity. The manufacturer’s declared accuracy of depth measurements for the DSTs used in the studies was +/- 0.4% of selected depth range, which was 50 m. The accuracy of the temperature measurements was +/- 0.1°C and the accuracy of salinity measurements +/- 1 psu. The sampling rate differed between and within years, depending on the tag memory, tag type and the aim of the particular study. The densest (highest frequency) measurements were collected over shorter periods within the summer, when recording intervals of up to 5-10 seconds were used to obtain more detailed information on the vertical distribution and on the actual swimming between depth layers.