John Fredrik Strøm

1 INTRODUCTION Sea trout, the anadromous form of brown trout Salmo trutta, has been pursued by anglers for centuries and still holds substantial recreational and economic value (e.g., Butler et al., 2009). This is partly due to its high food value and enticing fighting abilities for anglers, but also because of its accessibility to fishers, with viable populations found in small brooks and streams, as well as in larger rivers (Thorstad et al., 2016).

Receiver deployment A total of 98 acoustic receivers were deployed in Frakkfjord March 2019, while 49 acoustic receivers were deployed in Olderfjord in May 2019 (Figure 1). We opted for a grid design with receivers positioned uniformly across the study areas, as this enables an unbiased and near-continuous monitoring of the behaviour of tagged fish (Kraus et al., 2018; Peterson et al., 2021). Receivers were typically separated by about 500 m.

Previous electronic tagging studies on the horizontal migration of Atlantic salmon have either been limited by only describing the first part of the ocean migration [7, 8] or by describing coarse spatial distributions [12, 13].