Validation of a Long-range Dual Frequency Identification Sonar (DIDSON-LR) for Fish Passage Enumeration in the Methow River
A DIDSON-LR (Sound Metrics Corporation, Kenmore WA, www.soundmetrics.com ) was operated in parallel with visual observations to validate reliability of the instrument to enumerate fish passage in an open river. We found that even when operated at its lower frequency (0.7 MHz), the DIDSON-LR provided images of sufficient resolution to distinguish passage of fish (salmon/steelhead) at distances up to 40 m (the limit of our tests). However the level of resolution was limited, and that to distinguish between salmon/steelhead (60 to 100 cm) and large (20-50 cm) largescale suckers (also present at the counting site), the observer had to rely on both the relative size of the image and a difference in swimming pattern between species. The DIDSON-LR provided no means to distinguish between species with overlapping size ranges (Chinook salmon and steelhead). When operated at its higher frequency (1.2 MHz) the DIDSON-LR provided images of improved resolution, although the maximum distance at which it could be operated was with a 20 m Window Length and a Start Length up to 13 m.
Funding for this project was provided through a grant from the Pacific Salmon Commission – Southern Fund.
Galbreath, P.F. and P.E. Barber. 2005. Validation of a Long-Range Dual Frequency Identification Sonar (DIDSON-LR) for Fish Passage Enumeration in the Methow River. Columbia River Inter-Tribal Fish Commission Report reference #05-04, Portland, Oregon.