Fig. 1

Manual tracking using the Gain Reduction Method for measuring longitudinal (a) and lateral (b) position of the tag based on signal strength (SS). Longitudinal position was measured by sweeping the antenna along the stream path to determine signal strength, following the strongest signal, and reducing the gain while nearing the tag. Lateral position was recorded when the strongest signal strength and the lowest possible gain were noted when standing perpendicular to the flow and continually tilting the antenna up and down to pinpoint the tag