A system for automatic recording of fish tagged with coded acoustic transmitters

A telemetry system designed to automatically record the presence and swimmi ng direction of fish tagged with coded acoustic transmitters is described. The present paper presents results from an extensive mapping of signal stre ngths and the proportion of correctly identified codes from a transmitter a t various positions outside automatic listening stations (ALS). The system is evaluated on the basis of two field seasons, during which 107 Atlantic s almon, Salmo salar L., were tagged with acoustic transmitters in a fjord sy stem in southwestern Norway. By installing one ALS (two at high water disch arges) in the mouth of the River Suldalslagen and two ALSs in the Hylsfjord , the presence and swimming direction of all tagged salmon entering the riv er and the inner part of the 750-m-wide Hylsfjord were recorded.