Robotic turtles used for surveillance could help avoid escapes from salmon farms.

A sea cage can hold 200,000 farmed salmon at maximum. If the cage endures damage, such as a hole in the nets, the fish could swim out via the opening and make their running away in short order.

The aquaculture industry wants to prevent this scenario. Not only do escapes lead to huge losses for the industry, but no one wants farm-raised salmon to mingle and breed with wild populations.

Checking on what is going on inside the cages is important for being able to reply and repair any damage on time.

Watching life in the cages is important for many reasons as well, such as making sure good fish welfare: what is the health state of the fish? How critical is the salmon lice problem? Do the cages need to be washed?

Human divers and underwater vehicles handled by operators on land are usually used to check the conditions in sea cages. Both types of impostors can disrupt and distress the fish.

These methods also restrict the frequency of inspections.

Robotics and biology researchers have been struggling to find out which monitoring methods bother fish least. The trials that have a robotic turtle swimming around the cage to record the equipment and fish have confirmed to do the inspection job gentler and better.

The experiments show that the fish are only slightly scared or stressed by the robotic turtle. They swim peacefully and fairly close to the turtle, while they keep away from the impostors in experiments with thruster-driven underwater robots and divers.

“The general purpose of the experiments wasn’t just to test the turtle robot, but also to inspect what features robots being used in the aquaculture industry should have,” says Maarja Kruusmaa, Lecturer at Tallinn University of Technology and at the Norwegian University of Science and Technology’s (NTNU) Department of Engineering Cybernetics.

“We’ve found that the most important characteristics of the surveillance robot are its speed and size, whereas motor noise and colour hardly matter at all,” she said.

The turtle robot’s tiny size and slow movements are the features that make it less disturbing to the fish. The fact that it looks like an organism that lives in the ocean is less significant.

“The deduction turned out to be the contrary of our expectations. The fact that the robot looks like a marine animal doesn’t seem to play any part at all and that’s actually good news – it means we don’t have to make the robots to be fish- or turtle-like. That will make it inexpensive to develop and use robots in this new field of application to watch marine organisms,” Kruusmaa says.

The research shows which factors are vital when developing robots for the fish farming industry or for watching fish in their natural setting.

Jo Arve Alfredsen, an Associate Professor in the Department of Engineering Cybernetics at NTNU and Kruusmaa, issued an article about their findings in Royal Society Open Science about their discoveries. Kruusmaa is the first author.

Alfredsen and Kruusmaa are both employed by NTNU AMOS – the Centre for Autonomous Marine Operations and Systems. AMOS is making new types of underwater vehicles and new offshore monitoring methods as their emphasis areas.

Robots like the robotic turtle can offer fish breeders with online updates and monitoring of life in the sea cage. The turtle can also be linked to various sensors and measuring instruments.

Using robotic technology rather than divers for surveillance lets monitoring to continue without interruption. This continuity can add to quicker responses, better predictability, better fish welfare and lower death.

The researchers conducted the practical experiments in SINTEF Ocean’s full-scale aquaculture laboratory ACE, run by SalMar as part of the EU project AQUAEXCEL2020.

The turtle robot, known as  U-CAT, was developed at Tallinn University of Technology in Estonia and was initially designed for subaquatic archaeology applications. The idea was to use it to explore shipwrecks on the seafloor, so it was designed as a tiny and very maneuverable robot.

Alfredsen found out that the robot could be used in aquaculture because it had specifically these properties.

 

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