The Snapshot Flux Estimator - An Alternate Method for Estimating Migrating Adult Salmon Flux in Rivers Using DIDSON Imaging Sonar Data

      DIDSON imaging sonar systems are widely used to enumerate migrating adult salmon populations in Canada and the United States of America. Most projects use manual counting techniques with trained observers counting each fish image in a file or a timed subset of a file. Manual counting has proved accurate and precise but tedious and time consuming for data processing personnel in the field, especially when the numbers of migrating fish are extremely large. We derived an alternate method of determining the numbers of fish in a DIDSON file that uses fish speed, mean range of migration and time in the acoustic beam to derive estimates of salmon flux (fish/second) and therefore the total number of salmon in the data file. We found this alternate method produced results not significantly different from the manual counts produced by experienced observers. The method can be faster to perform than manual counting, especially for files with large numbers of migrating fish. The entire collected file can be used to make the estimate, as temporal sub-setting to reduce effort is not required. Streamlining of the existing software could be done to further speed up the analysis process. Manual counting of some data files is needed to act as a check on the accuracy and precision of the Snapshot method.