Echo-sounding used to count farmed fish – without all the hassle

It's very important for fish farmers to keep track of the number of fish in their pens, but doing so typically involves going in and actually netting out some of the fish. According to new research, echo-sounding tech could soon serve as an easier and more accurate alternative.

Not only is periodically capturing some of the farmed fish difficult and time-consuming, it's also stressful to the animals, plus it doesn't always provide an accurate estimate of fish populations. That's where the echo-sounding approach comes in.

The sonar-like technology – which involves sending acoustic pulses down into the water, then detecting their echoes off of submerged objects – is already widely used in commercial fish finders. Such devices are typically just used to show the location and approximate size of shoals, however. Assessing actual numbers of fish can be difficult, as the animals at the top of the shoal tend to shield those underneath from the acoustic pulses, so they're not clearly detected.

As part of the EU-funded PerformFISH project, scientists from Norway's SINTEF institute and Greece's Hellenic Centre for Marine Research (HCMR) set about addressing that problem.

Doing so involved starting with two pens – each one containing a known number of salmon – that had an echo-sounder located between them. The researchers then proceeded to take readings while varying the distance between the two pens, along with the distance between each pen and the echo-sounder.

By comparing the device's various readings with the known number of fish in the pens, it was possible to identify a consistent relationship between the information provided by those readings and the actual fish numbers. The echo-sounder could then be calibrated to provide what proved to be reliable estimates of fish density within enclosures.

"We are making exciting progress and I am looking forward to developing this further," says SINTEF's Dr. Walter Caharija. "We are building a foundation from which we are learning how to utilize an echo-sounder to better estimate biomass in a production net pen."

Norwegian company Kongsberg Maritime has expressed an interest in commercializing the technology.

Source: AquaTT