Hakai Magazine

Coastal science and societies

Cod can be trained to respond to sound cues, and trained fish will pass on this behavior to wild fish. Photo by Alex Mustard/Minden Pictures

Oh, Give Me a Home Where the Wild Cod Roam

A novel application of auditory training opens the door to more efficient cod ranching.

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by K. N. Smith

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It took a week for Björn Björnsson to train 20 wild cod. In a compelling demonstration of classical conditioning, the aquaculture researcher at Iceland’s Marine and Freshwater Research Institute taught the fish to associate a low-frequency sound with a free meal. It only took another day for Björnsson—with the help of one of his trained fish—to teach another 19 wild cod.

People might not think of cod as herd animals, but Björnsson says cod are adept at reading social cues to learn where to grab a bite. The end result of this training? Dozens of Atlantic cod congregating around a floating platform moored in an Icelandic fjord, ready to be plucked from the water in a fisher’s net.

In a case of the Wild West meets the open ocean, fish ranchers may one day ride the watery range with boats instead of horses, dropping forage fish into feeding stations and taking stock of their herds with sonar.

Fish ranching—rearing stocks of free roaming fish—falls somewhere between traditional commercial fishing and fish farming. Proponents like Björnsson say ranching is more efficient than farming and results in fewer accidental catches of endangered species or young cod than traditional fishing. In previous, larger-scale experiments that didn’t employ sound-based training, Björnsson and his colleagues found that just by leaving feeding stations in the water, thousands of adult cod would gather around. He says smaller fish species and younger cod tend to avoid the herds—probably out of fear of being eaten. A 2012 paper, also by Björnsson, showed that ranching has the potential to yield higher profit margins than fishing or fish farming.

Fish ranching is not an entirely new idea: it’s been tried in Norway with wild saithe (a fish in the cod family), in Japan with red sea bream, and elsewhere. The addition of sound-based training, however, has the potential to make it even more effective.

Yet aquacultural engineer Boaz Zion, of Israel’s Agricultural Research Organization, says that even after nearly 20 years of effort, proponents of fish ranching have produced little momentum. Björnsson and others have “a long way to go proving the concept in a way that will convince commercial fishermen to get into it,” says Zion, who was not involved with the research.

Björnsson understands why fishers and farmers are skeptical—and the problems may have more to do with policy, law, and economics than the effectiveness of his technique. He says for ranching to be economically viable, ranchers would likely need exclusive rights to the area around their feeding stations to prevent other fishers from reaping the benefits of their investment. This idea, he says, is likely to be unpopular with commercial fishers. Aquaculturists accustomed to net pens, meanwhile, are reluctant to invest in free-ranging fish that could potentially wander off. But if these and other problems could be solved, Björnsson estimates that cod ranching could account for around 10 percent of Iceland’s annual catch.

Of course, fish ranching using sound has problems of its own. Adding more sound to the ocean could exacerbate sound pollution, which already troubles many marine species. The sound needed to herd cod, however, can be quieter than the engine of a large vessel—as long as feeding stations are close together, Björnsson says.

Whether fish ranching will ever transform the open sea into the open range is anyone’s guess right now, but Björnsson plans to continue his research. “Few fishermen are going to read these papers,” he says. “But hopefully some younger scientists will be inspired by these studies and are able to bring the idea a bit further.”