Use of radio telemetry for studying upriver migration of adult Atlantic salmon (Salmo salar)

Abstract

This paper describes and evaluates a 50 mHz radio telemetry system for studying river movements of adult Atlantic salmon (Salmo salar). In fresh water for most applications radio telemetry is preferable to ultrasonic telemetry, because the receiving element (antenna) can be above water, and radio signals are scarcely affected by turbulent, weedy or ice‐covered water. Within the range of 10–200 mHz higher frequencies are preferred, since the efficient antenna size is inversely proportional to frequency, and attenuation of signals is independent of frequency. Transmitters were cylindrical (6.5–9.6 cm long * 1.9 cm diam) with a 0.5 wavelength antenna trailing from one end. Each emitted pulsed signals on one of 20 crystal‐controlled channels between 49.100 and 49.385 mHz. Transmitters were placed in the stomachs of salmon and the antenna trailed out the last gill slit. Receivers were portable 20‐channel manual or automatic scan models, and antennas were 48 cm diam capacitor tuned loops. Some salmon regurgitated transmitters. Two salmon were recaptured and showed no ill effects from carrying transmitters for 32 and 42 days. Pulse rate had little effect on known transmitter life under natural conditions. Known tag life was variable, but averaged 70 days for transmitters with 1000 mah batteries. The range of transmission of transmitters to a receiving system in an airplane at 410 m altitude was about 10 km, and to a boat about 1 km. Range to a land vehicle was variable depending on obstructions. From the airplane transmitters can be located within a radius of about 50 m.