Fish answer call of cod

Training fish to returnto a sound may solve the problems of dwindling sea stocks, environmental damage and taste. Geoff Watts reports.

As a way of harvesting protein, commercial fishing has its drawbacks. Besides being hard and dangerous work, often carried out far from home, it offers no guarantee of success. Fish farming, by contrast, is less arduous, less dangerous and more reliable. Small wonder that it now provides a quarter of all the fish we eat.

But fish farming has its price too. Its methods are accused of damaging the environment, contributing to the spread of disease among fish and delivering a product that lacks the taste of its free-living counterpart.

A fisheries biologist in Plymouth thinks he can see a way of combining the best of both approaches. Improbably, his suggestion comes from experiments in which fish are trained, like Pavlov's dog, to recognise and respond to particular sounds.

Until four years ago, Jonathan Lovell was the skipper of a commercial fishing vessel. Like many in the industry, he decided that its diminishing rewards no longer justified the effort of staying in business. So he took a degree in fisheries science and is now doing a PhD at Plymouth University's Institute of Marine Studies.

His lab on the top of the building features several fish tanks and various bits of slightly ramshackle electronic equipment. Like most fish in most aquariums, Lovell's experimental subjects spend their time gliding slowly and aimlessly around their confined world. Suddenly, though, the mood in a tank will change. It happens when a small speaker mounted at one end is activated to emit a short pulse of sound.

Showing their first signs of purposeful movement, the fish dart to the end where the speaker is mounted. These graduates of Lovell's training programme have learned to associate a specific sound with the presence of food. Indeed, no sooner do they arrive than a small hopper above the tank delivers their reward.

Sound travels long distances through water, and fish have good hearing. It takes about three weeks to teach them to associate the presence of food with a particular noise. One that Lovell uses - it resembles a grunt - is based on the mating call of the cod. "If I was a cod," he says, betraying a thought process that may not be entirely scientific, "I would respond to a mating call more than any other sound."

Moving from laboratory fact to commercial aspiration, Lovell reasons that fish bred in captivity could be taught the trick, then released to forage in the sea for themselves. However, on hearing the learned sound - played perhaps twice daily - he believes they would return to a feeding station, so long as it continued offering them a guaranteed source of extra food.

To haul in their free-range fish, owners would attract them one final time to the feeding station. "You would then have a specially designed net that could be pulled around the whole shoal. And if you'd taught different year classes to respond to different sounds, you could bring in, say, just the three-year-olds."

At the moment Lovell is working with carp, grey mullet and bass. He hopes to extend his research to the major commercial species. There are, of course, several potential pitfalls. Poaching, for example. A rival who had discovered your signal could play the Pied Piper and lure your stocks to his nets. Lovell, though, thinks that problems like this can be overcome.

"These are going to be marked, domesticated fish that just happen to be living free in the environment," he argues. "They will be my property." In other words, while there may be nothing to prevent a fish thief stealing from Lovell's shoals, such individuals would be in much the same position as anyone caught poaching from a private trout stream, or rustling sheep that were being grazed on common land. Protection for new-wave fish farmers would lie not in technology, but in the ordinary laws of property.

The wider issue driving Lovell's work is the question of sustainability in commercial fishing. The problem, he believes, is to do with ownership - or rather lack of it. "Why conserve something that doesn't belong to you? The moment I own the fish I become interested in conserving them. At the moment I don't own the fish in the sea. Nor does anyone. This is why fisheries are collapsing."

Conventional fish farming, of course, solves this question of ownership and, in its first phase, has few damaging effects. "Modern intensive hatchery systems are good at using enclosed tanks to rear small bass from eggs until they're up to a few centimetres long," Lovell concedes. "The problems lie in growing them from that stage to a marketable size of about 24cm." It is this phase - when the fish are still captive but transferred to cages placed in the environment - that creates the battery-farm problems of disease, pollution, overuse of antibiotics and the rest.

Lovell has already tried his methods in a pond-sized environment. The big test will come in the spring, when he intends to carry out a field trial using 10,000 juvenile bass. The fish, each about 4cm long, will be trained in tanks in his lab. From there they will go to an enclosed feeding station in Plymouth Sound for a two-week acclimatisation period. The doors will then be opened, allowing the fish to swim free.

If they do not return when Lovell summons them, he will have kissed goodbye to 10,000 fish. If they do, he will have taken the first step towards a new kind of fishing.