Using a Geographic Information System to Assess the Accuracy of Radio-Triangulation Techniques for Fish Telemetry

Abstract

We evaluated the accuracy of several triangulation methods that produce quantified rather than inferred transmitter position data on the movements of brown trout Salmo trutta in an urbanized stream. Other telemetry studies have reported accuracies of 0.5-5 m based on visual observation of fish or detection of hidden transmitters from within streams. With our geographic information system (GIS) method, coordinate locations for each transmitter position were recorded without entering the water. A global positioning system (GPS) was used to record coordinate locations on the stream bank and compass bearings with signals of hidden transmitters in the stream. Signal locations were then triangulated to estimate the coordinates of transmitter locations. Location coordinates were placed onto a GIS coverage, and accuracy was determined by comparing the actual positions of hidden transmitters with the estimated positions. Three different triangulation methods produced slightly different accuracies. Our GIS method is less biased and supported by data and could provide a standard method for triangulation. Moreover, the GIS-based radio-triangulation approach enables tracking in the field without disturbing a tagged fish in its habitat or otherwise altering a fish's behavior due to human intervention.