Tucked within Norway’s fjord-riddled coast, nearly 3,500 fish pens corral upwards of 400 million salmon and trout. Norway exports more such fish than any other country in the world (1.1 million tons in 2018), and farmed salmon is one of its top three exports. With the global industry expected to quintuple by 2050, farmed salmon is a fine kettle of fish.
But raising salmon is not without challenges. Feeding them is expensive. Parasitic crustaceans called sea lice (Lepeophtheirus salmonis) attach to their bodies and graze on skin, blood, and mucus. If the lice don’t kill the fish, some delousing methods, such as flushing the fish with water, might. About 15 percent of farmed salmon die annually, according to Norway Royal Salmon.
Now, a new remote-controlled fish pen—the first of its kind designed for the tempestuous waters of the open ocean—could help Norway meet the growing demand for salmon, reduce the cost of feed, and prevent deaths from sea lice.
In 2020, the first pen will be tested off the coast of the county of Troms, near a small island that will help abate the rough waves. If the field trials go well, the pens could be moved further out to sea.
Instrumented with wireless gauges, sensors, and cameras, the sea pen will allow workers onboard a nearby barge to monitor the fish and the system’s automatic feeders. The feeding system reduces the energy cost of feeding by 50 percent compared with conventional methods. And because these open-ocean pens will keep salmon 10 to 40 meters beneath the surface, below the sunlit zone where sea lice and algae thrive, they could reduce or eliminate the need for delousing operations and significantly lower mortality rates.
The system, developed by Arctic Offshore Farming (owned by Norway Royal Salmon), resembles a giant fish basket. The cylindrical pen has a diameter of 79 meters and consists of a top and a bottom section. Each has a buoyant pontoon ring. When submerged, only the upper pontoon is visible on the ocean surface. Salmon live in the bottom section, in a large net that drapes to a depth of 40 meters from the lower pontoon. A net prevents the fish from swimming into the top section and can be removed to add fish or harvest them.
Fish need air to fill their swim bladders, so the pen has four decompressors that create air pockets beneath the water. Camera and oxygen sensors monitor the air pockets and automatically engage decompressors to keep them full at all times. The pontoons keep the pen stable, says Klaus Hatlebrekke, chief operating officer for market and business development at Norway Royal Salmon. “Even in a model test of a 50-year storm, we were not able to disrupt the air pockets,” he says.
As with traditional salmon farming, the salmon will be raised from eggs to juveniles, called smolts, onshore in freshwater hatcheries. After a year, the smolts are transferred to a saltwater sea farm in a fjord. Under conventional methods, they would stay in the fjord and be raised until they weighed 5 kilograms. But with the new system, fish weighing 1.5 kg will be moved to the open-ocean pens, where they’ll remain for another 10 to 11 months before they’re harvested.
Using a local area network, the sensors transmit data to an onboard server that’s connected via a fiberoptic cable to a crewed feed barge stationed about 400 meters from the farm. One barge can monitor a cluster of fish farms and restock them with feed pellets every 7 to 14 days. With a volume of 120,000 cubic meters, each pen can hold up to 600,000 fullgrown salmon at a time.
Standard feeding systems blow feed pellets through air hoses floating on the water’s surface. But this approach doesn’t work in the open ocean, where waves and winds would scatter the feed out to sea. Instead, the new feeding system automatically releases the feed underwater one to three times per day, allowing currents to distribute the pellets. Cameras allow crew members on the barge to see where the fish are located and release feed in those areas, reducing waste.
Although jobs in salmon fishing are about to get more technical, they don’t have to be more complicated, says Lars Andersen, a sales specialist in aquaculture at ABB. The company built an interface for the salmon pen that displays the controls and safety systems in a simple dashboard.
As for the fish, their experience will more closely represent a life lived in the wild, says Hatlebrekke. Wild salmon that begin their journey in freshwater rivers spend only a few weeks in the sheltered fjord waters before they swim out to the open ocean. As farmed salmon operations incorporate more technology, the lives of farmed fish could mimic this path from freshwater to open sea, for a more natural existence. —Tracy Staedter
A version of this article appears on our Tech Talk blog.
POST YOUR COMMENTS at https://spectrum.ieee.org/salmonfarm0919