Sonar Population Assessment method

​The purpose of the Sonar project is to bring new technology to salmon research in the Miramichi River. We are using sonar (SOund NAvigation and Ranging) for counting Atlantic salmon. ​Sonar allows fast and accurate fish stock estimates. ​ When the information of returning adult salmon is available faster, it is possible to make in-season fisheries management decisions based on collected data.​ This website is one example of the usefulness of this data. We will be updating the numbers of fish we have detected using our sonars during the salmon migration season.

In 2019, the sonars record video material in Miramichi River 24 h a day, 7 days a week in the Little Southwest Miramichi @ Upper Oxbow

The sonars are located underwater near the riverbanks with their 96 beams projecting across the river. Each sonar field covers approx. 30 meters  of the width of the river, aimed in an area where fish are likely to be travelling. Depending on the width of the river, multiple sonar units may be required to cover the whole width of the river, and in future seasons, small guiding fences will be installed to guide fish to sonar. Similar to a security camera recording, the sonars record 24 h a day 7 days a week, from May to November.

Unlike an underwater video camera, the sonars can detect fish even in no-light or “turbid” conditions, for example at night or during a flood, as the data is collected as sound that is turned into a visual image.
​
​The sonars are placed in the river in the most suitable locations. The study sites were selected using bathymetric maps and other available information.

One advantage of using sonar method to count fish in rivers is the processing time. Daily or weekly updates about the stock size help fisheries management: fishing can be controlled based on actual numbers of fish. 

We are testing the process and analysing the material daily. We are currently able to make updates at least weekly, usually more frequently.

A research component is developing a method to computerize the fish counting, so that both counting and species identification will be automated.

The fish counting process

We visit our study sites daily to obtain the video data. The data are processed in our office at the MSA hatchery in South Esk, where professionals analyse the material and measure all the fish from the videos. 

Each day, we know how many fish swam through our study site the day before and their sizes.

Challenges for sonar fish count in Miramichi River

We are currently only able to report the number of fish and different sizes. For example, the graph showing counts of grilse-sized fish may include other species such as Striped bass and American shad. However, the migration timing, and fish behavior helps us deciphering the species composition.

Another research project is ongoing to find a solution for this challenge.