This study was initiated by concern for Lower Nass River and Coastal Nass Area pink and chum salmon stocks and the implementation of the Nisga’a Treaty, which requires an improved understanding of the accuracy of the escapement estimates in the Nisga’a Treaty area. Traditional estimates of pink salmon escapement in this area were based on aerial surveys of adult fish in the main creeks and rivers during the peak spawning period.
The goal of this project was to use visual observations (tower counts) in conjunction with hydroacoustic estimates to derive independent escapement estimates. Hydroacoustic assessment of adult salmon in rivers typically involves a form of tracking, either with a computer-driven algorithm or visually counting echo-traces.
However, the dense schooling behavior of pink salmon in the Ksi X’anmas River made it impossible to resolve individual fish tracks. We therefore explored the feasibility of using echo integration, scaled by tower counts. Angle echograms allowed us to distinguish upstream and downstream swimming schools. The results of the echo integration correlated well with tower counts and suggested that aerial surveys may have been underestimating escapement by as much as a factor of six. In addition, the acoustic data provided the following valuable insights into the tidal and diel patterns of pink salmon migration in the Ksi X’anmas River: The strongest peaks of fish passage occurred on large tides during daylight hours; some fish movement was triggered by dawn and dusk; and very little to no net upstream movement was seen at night. (See Miscellaneous for more information on the creation and interpretation of split-beam angle echograms similar to the one shown in the image on the right).
Reference
Bussanich, R. J., Bocking, R. C., Degan, D. J., and A.M.Mueller. 2003. Fixed-location hydroacoustics as a method of enumerating adult pink salmon in the lower Ksi X'anmas - A comparison of visual counting and split-beam acoustics (2001-2002). Report prepared for Nisga'a Lisims Government, New Aiyansh, British Columbia.