Home on the Fish Range
If the term "sea ranching" doesn't yet ring a bell, hold your salmon fork, it soon may.
No doubt you know about fish farming. Nearly half the fish we consume globally is "farm raised" in cages or pens that can hold thousands of animals at once and are typically kept in lakes or coastal waters. This efficiency exacts a toll: the sewage generated by fish farms, and the nutrients and antibiotics that are pumped into them, pollutes the local environment, and the diseases and parasites that thrive among the crowded, farmed fish readily spread to wild ones.
But imagine a different model. What if, instead of being factory farmed like veal, fish could be let out to pasture like old-school cattle? They’d spread out, range freely, forage and fatten up in the wild. Then, weeks or months later, they could be called back in -- using the aquatic version of a cowbell -- and harvested. "Call and catch," as Boaz Zion, a scientist at the Agricultural Research Organization in Israel, puts it. Although sea (or "acoustic") ranching is still very much in its infancy, Zion and his colleagues have conducted several field experiments that suggest it can work, and they’ve built what he calls "an automatic fishing machine" to prove it. "What we want to do," he says, "is turn huge coastal regions into grazing fields of fish."
The concept builds on several established, if under-appreciated, facts about fish. For starters, fish can hear. They can distinguish between different audio tones or patterns, even -- in the case of koi carp -- between classical music and blues. And as the volume of manmade aquatic noise rises, it’s becoming clear that fish, not to mention whales and dolphins, are adversely affected. Acoustic ranching would attempt to harness this vexing relationship: instead of simply damaging sea life with our sounds, we’d tame it.
Indeed, fish can be trained; they learn and remember. In the 1980s, research in Japan and Norway showed that if free-swimming fish (including salmon and red sea bream) listen to an acoustic signal while eating at a feeder, they soon are conditioned to associate the sound with food. Play back the sound and the animals come looking: call them Pavlov’s fish. However, the research was never developed into a way to condition young fish and ultimately harvest them, Zion says. His own studies, in contrast, have aimed to "close the circle."
Much depends on the piscine memory. How long does it take to condition a fish to a sound? How long does the association last? A few years ago, Scott Lindell of the Marine Biological Laboratory in Woods Hole ran some indoor trials with black sea bass and found they needed about four weeks to train to a sound. Zion’s work with carp and tilapia is more promising still. Three times a day he played an acoustic signal -- a pure tone at 400 Hz -- for five minutes while the fish were simultaneously given pellet snacks; they made the connection after just a few days.
Zion’s automatic fishing machine is essentially a floating fish pen and training cell, remotely operated and solar powered. In one study, he moored it in the middle of a large reservoir, stocked it with carp and tilapia, conditioned them on an audio tone for two weeks, then freed them to forage on their own. Every few days, to reinforce the link, the fishing machine broadcast its 400-Hz and provided a small snack to the gathering fish. Finally, after a few weeks, the tone sounded one last time for five minutes, a gate closed on the pen, and the researchers counted how many fish had come looking for food.
The results were encouraging. Although just 13 percent of the stocked tilapia returned, some two-thirds of the stocked carp came back, with additional tilapia, carp, and other species from the reservoir in tow. Indeed, the final catch contained two-and-a-half times as many fish as were originally stocked; evidently the acoustic training conditioned many of the wild fish within earshot. But it’s more than that, Zion notes. Fish are social; they follow friends and leaders. That suggests that, in practice, perhaps only some fish -- the Judas fish -- would need to be trained, to later lead their pals to harvest.
Creating a fish ranch is matter of scaling up. Fish would be fed, raised, and acoustically trained in lakes or along sea coasts for a relatively brief period, then freed. A manager might go out in a boat occasionally and provide a reinforcing signal and snack, Zion says, "to remind the fish that we have some relationship with them." When the time comes, we ring the dinner bell. "The story sounds too good to be true," Zion concedes. "It sounds like fantasy: you know, you whistle to the fish and … blah blah blah. But once you provide the evidence that you're doing it on a small scale, people get convinced and interested."
Having engineered the farmed fish -- reared salmon truly are the chicken of the sea -- we now are on the brink of creating its logical, if only slightly less unnatural successor: the free-range fish. Paradox aside, a fish ranch presumably would be cleaner and more sustainable than a fish farm; ranched fish wouldn’t need to be penned for nearly as long, so their upkeep -- and the associated nutrient and sewage waste -- would be significantly reduced. Feeding largely would be left to nature, or whatever you call a realm from which dinner can be beckoned at will. "We really do believe that the idea is a win-win," Zion says. "Whatever you don't harvest doesn't go down the drain, it's still out there. If it’s done in a balanced, controlled manner, maybe it's a way to revive the fish population."
Needless to say, the challenges abound. Some fish species are more readily trained than others; once ranchers identify which fish "work," they’ll likely need an incentive to respect nativity and not introduce alien fish with abandon. And of course, acoustic ranching won’t make the seas any quieter; one hopes that the dinner bells won’t bother the fish they aren’t meant to attract.
And then there’s scale. For all its faults, the fish farm is efficient precisely because it handles far more animals than a given area can naturally support. A fish ranch, in contrast, would be limited in size by the carrying capacity of its aquatic grazing lands. Production within means -- that’s the essence of sustainability. But like any industry, fishing is driven by demand, and among fish-eating consumers, the notion of sustainability has yet to catch on.