Tracking 48 and 150 MHz radio-tagged male Lake-trout during their spawning migration in a mountain regulated river

Abstract

Since 1991, the natural migration of trout (Salmo trutta L.) from Lake Geneva to the Lower-Dranse river has been jeopardized by a weir that trout apparently cannot pass. To estimate whether adding a fishway to this weir is useful, five male trout were surgically tagged with radio transmitters operating at radio frequencies of either 48 to 50 MHz and or at 150 MHz to localise eventual spawning grounds. Healing after surgery was very good despite the low water temperature (5.5°C). The 150 MHz system was easy to use and localised fish precisely. The trout migration area was located downstream from a hydraulic power station inducing peaking flows in this very turbulent upland river. Despite these difficult conditions, tracking the trout migration made it possible to localise probable spawning areas.