By Daniel Cressey of Nature magazine

Ranching cod off the coast of Iceland is far more financially sensible than conventional fishing methods or keeping the fish in cages, according to a new analysis.

Fish ranching -- where the animals are free to roam but trained to return to a certain point so they can be caught -- could one day become a significant part of global fisheries, fitting between traditional catching and aquaculture, says Björn Björnsson, the lead author of the study, published in Marine Policy on 1 April. It could even reduce the catching of fish that are not the target species or are undersized, says Björnsson, a fisheries scientist at the Marine Research Institute in Reykjavik.

'Ranching' allows fish to roam free but attempts to condition their behavior so they can be rounded up for feeding and eventual capture. Some researchers are experimenting with sound signals that condition the fish to return to feeding stations. But Björnsson's economic analysis is based on a simpler method, by which otherwise wild fish are conditioned by regular feeding at specific feed stations.

Based on data from an experiment off Iceland conducted in 2005-06, Björnsson estimates that ranching is the most profitable way of putting cod on dinner plates, followed by traditional fishing and then capturing wild fish for growing in pens.

He estimates that a typical fishing boat could make a profit of €71,000 (US$103,000), through traditional fishing, for 200 tons of cod. But the same boat involved in cod ranching could bring in more than 36 tons of cod with a net profit of €150,000.

"In the future, ranching in 'herds' could become a significant part of the fishing/farming industry globally," says Björnsson. "It will not have to reduce the conventional farming and fishing; it may rather increase the total yield of fish for human consumption."

And it could be done in an environmentally friendly way, he adds. Rather than indiscriminately netting all fish around the target animals, training a herd to respond to stimuli would mean fishermen could take just the species they were after at a time they were the right size.

Home on the range

Previous efforts at fish ranching have met with limited success. In the United States, even preliminary experiments with ranching using sound as a herding signal attracted a lawsuit over fears feeding the animals could cause pollution and disrupt ecosystems (see: Lawsuit chips away at fish research).

Ray Hilborn, a fisheries scientist at the University of Washington in Seattle, notes that the method used in this study differs from other types of fish ranching.

"The traditional approach is to hatch the juvenile fish in hatcheries, have them go and have them come back," he says. "[What Björnsson's team] are really doing is using feed to aggregate fish."

In this case, and in traditional fish ranching, there could be problems caused by the ranched fish competing with other animals and wandering into waters plied by traditional fishermen.

Scott Lindell, director of the Scientific Aquaculture Program at the Marine Biological Laboratory in Woods Hole, Massachusetts, notes that previous efforts at ranching have been scuppered by political and social arguments about who the fish belong to.

"It's feasible, but it requires as much social engineering as it does anything to do with fish," he says. Smaller bodies of water such as lakes might make ranching more feasible and small communities could find it easier to reach a consensus, he says.

"The economic feasibility is crucial in convincing the fishing and farming industry, the scientific community, research funds and authorities that it is worthwhile to develop this idea for the benefits of mankind," says Björnsson. "The controversial legal issues will be sorted out if this idea is the best to maximize yield from the wild fish stocks."

This article is reproduced with permission from the magazine Nature. The article was first published on April 13, 2011.