For fish farmers, tracking the number of fish in the purse is very important, but doing so usually requires actually getting some fish in the net. According to a new study, echo detection technology can soon be used as a simpler and more accurate alternative. It is not only difficult and time-consuming to catch some farmed fish on a regular basis, but it also puts pressure on the animals. In addition, it does not always provide accurate fish population estimates. This is where the echo sounding method comes in.
This sonar-like technology-which involves sending acoustic pulses into the water and then detecting its echo on underwater objects-has been widely used in commercial fish finder. However, this device is usually only used to display the location and approximate size of the fish school. Assessing the actual number of fish can be difficult because animals on top of the shallows tend to shield the animals below from the sound pulses, so they cannot be clearly detected.
As part of the PerformFISH project funded by the European Union, scientists from the Norwegian SINTEF Institute and the Greek Center for Marine Research (HCMR) set out to solve this problem.
To do this, you need to start with two purses—each purse has a known number of salmon—and an echo sounder between them. Then, the researchers continued to take readings while changing the distance between the two fences and the distance between each fence and the echo sounder.
By comparing the various readings of the device with the known number of fish in the pen, the consistent relationship between the information provided by these readings and the actual number of fish can be determined. The echo sounder can then be calibrated to provide a proven estimate of fish density in the purse.
“We are making exciting progress and I look forward to further development,” said Dr. Walter Caharija of SINTEF. “We are building a foundation from which we are learning how to use echo sounders to better estimate the biomass in the production fence.”