Monitoring Atlantic salmon (Salmo salar) populations using imaging sonar technology in the Miramichi River

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University of New Brunswick
Atlantic salmon (Salmo salar) is an important species culturally and socially, and a target species of multiple fisheries globally. Primarily due to overfishing, water pollution, sedimentation, and damming, Atlantic salmon catches at sea are under a continuing decline; however, the state of different populations varies greatly, and it is important that each population is assessed accurately and independently. In this PhD research, non-invasive imaging SONAR technology was tested for collecting tributary-specific information about migrating fish in the Miramichi River, where the adult Atlantic salmon population is currently monitored using a traditional mark-recapture method. The accuracy and precision of the length measurements using long-range (up to 30m) imaging sonar data was tested and deemed low; however, a Bayesian model was created with capacity to predict the size class of adult Atlantic salmon from the sonar measurements. For efficient analysis of the sonar data, an automated data processing workflow was created. The automation counted the number of migrating fish similarly as different human-generated counts (with mean of differences between -39 % and 65 %). The tail-beat frequencies of three-fish species (Atlantic salmon, striped bass (Morone saxatilis), and American shad (Alosa sapidissima)) were calculated from the sonar data and found significantly (p<.05) different from each other. An automated method was developed showing promising results that can be further developed into models distinguishing different species using sonar data. Finally, underwater camera sampling was used for apportioning species in the sonar data in the Little Southwest Miramichi River. Hourly migration data indicated that both salmon and striped bass were rarely detected during daylight hours. When compared to downstream trap net catches that were adjusted for realistic values from literature (catchability 10 % and 40 % of fish moving to the same tributary), the counts were in close agreement for Atlantic salmon (sonar count 103-130 % of the adjusted trap net catch). To combine all the information gathered throughout the project, a guide was produced for monitoring Atlantic salmon in rivers using imaging sonars. In conclusion, the imaging sonar method provides an efficient and non-invasive method for population assessment in the Miramichi River.