DEER ISLAND, NEW BRUNSWICK — On land, strewn across the pebbly beaches of this quiet island, the sea cages look like a fleet of alien spacecraft. Their ring-shaped plastic floats, some 20 feet in diameter, await repair.
After their nets are attached, they'll join hundreds of other sea cages anchored off the foggy Fundy coast, whose waters teem with salmon being fattened for US dinner tables.
Such cages are at the center of a debate over the environmental impact of a rapidly expanding industry known as aquaculture.
New Brunswick salmon are part of this global industry - one that has doubled in size over the past decade and now accounts for a quarter of the world's food-fish supply, according to the UN Food and Agriculture Organization.
Proponents say aquaculture can reduce pressure on wild stocks of fish and provide new jobs, while helping to feed Earth's rapidly growing population.
Yet critics fear that intensive aquaculture operations are stressing seas, estuaries, and coastal ecologies often already damaged by overfishing, coastal development, and pollution.
"Aquaculture is going to grow because there simply will not be a supply of [wild] seafood products based on capture fisheries," says Leroy Creswell, an aquaculture research scientist in Fort Pierce, Fla., and a former president of the World Aquaculture Society.
"Many species are tapped out and in may cases have crashed or are in rapid decline. Aquaculture is needed to bridge the gap."
Asian shrimp farms are blamed for the poisoning and destruction of mangrove forests, key nursery habitats for many marine creatures. United States and Canadian salmon farms are blamed by many for contributing to declines in water quality, wild salmon populations, and deep-sea schooling fish that are caught and ground to feed penned salmon.
Salmon farms: Clean up your act
"It's an enormous industry and it's not just going to go away," says Frederick Whoriskey of the Atlantic Salmon Federation, a conservation group based in St. Andrews, New Brunswick. "We need to find solutions so that salmon farms clean up their act and function sustainably."
Freshwater aquaculture has been around for a long time. It is thought to have started in China about 5,000 years ago with the advent of carp farming. Then, as now, the closed carp ponds were fertilized with animal manure, producing the algae, plankton, and plants eaten by the fish. China still rules the roost today, accounting for nearly two-thirds of world production, much of it carp.
Today aquaculture is becoming as diverse as conventional agriculture. Seaweeds are harvested from Japan to California for industry, fertilizer, and food.
In some parts of the US, clam diggers plant sprats on their mud flats and collect them when they've grown, while oyster and scallop banks are often enhanced by planting hatchery-grown sprats. Cod, halibut, and sturgeon may soon join salmon growing in coastal sea cages.
The vast majority of the world aquaculture industry farms with little impact on the environment.
Freshwater carp, catfish, and tilapia are plant-eaters usually raised in special ponds where they help convert potentially harmful organic wastes into edible fish meat.
Shellfish like mussels, scallops, and oysters filter algae and plankton from seawater, so farmers don't add feed or medicine to the environment.
But the farming of other species - particularly shrimp and carnivorous fish like salmon - can be extremely destructive. Salmon are fed processed fish meal made from other fish.
Uneaten feed, fish wastes, and antibiotics fall from their crowded cages and are blamed for deterioration of water quality, bottom habitat, and disease outbreaks in wild fish populations.
And since farmed salmon and shrimp (normally a scavenger) are fed meals and oils made from small, edible schooling fish like mackerel, caplin, sardines, and anchovies, opponents point out that the farms are net consumers rather than producers of fish protein.
"By taking these fish out of the ocean to feed to farmed fish, we're undermining the integrity of the marine food web," says Rebecca Goldburg, staff scientist at the Environmental Defense Fund (EDF) in New York.
"On land we grow herbivores like chicken and cattle because it's an efficient way to make protein. It makes no more sense to grow carnivores in fish farms than it does to grow tigers on land."
According to a recent EDF report, US aquaculture operators have been authorized by the US Fish and Wildlife Service (USFWS) to kill a wide variety of birds that prey on farmed fish - particularly catfish, the most-farmed species here.
Nearly 52,000 birds were legally killed at US aquaculture facilities under legal permits in the four years between 1989 and 1993, according to USFWS data. Double-breasted cormorants represented half of the total, which included 9,443 great blue herons, 4,243 great egrets, and about 1,200 kingfishers.
Conservationists are also concerned about the shooting of seals and sea lions by salmon farmers trying to protect their teeming sea cages. Many Canadian farmers have installed underwater sound devices intended to drive away seals, but they may also be scaring humpback and minke whales feeding in these areas.
"Acoustic devices are keeping away the whales and possibly even the schools of herring that many other creatures rely on away from whole areas of the coast," says Inka Milewski of the Conservation Council of New Brunswick, which opposes further expansion of the province's large salmon industry.
Proper context needed
Aquaculture proponents admit that salmon farms have had negative impacts, particularly when overcrowding is allowed. But they say these problems must be understood in proper context.
"It's in the industry's own best interests to maintain the best possible environmental quality - the fish depend on that," says Jay Parsons, a researcher at the Memorial University of Newfoundland and former president of the Aquaculture Association of Canada. Proponents point out that the environmental impact of salmon or shrimp is far less than that of other industries that pollute the marine environment.
"Paper mills, oil spills, and municipal sewage all pollute the environment," Mr. Parsons says. "I'm not saying there aren't problems, but there are a lot of other things we should be concerned about that have a far greater impact than salmon aquaculture ever will."
Under pressure from regulators and sport fishermen, the industry is reportedly working on plant-based feed products and improved husbandry practices that reduce the risk of disease and pollution. Switching to closed-loop farms on land is an option that would reduce the impact of salmon farms by monitoring and treating waste water before it is released.
"Most people involved in aquaculture have a strong commitment to creating a responsible, sustainable industry," says aquacultural scientist Creswell. "But we can't do things with zero impact any more than you can drive a car to work or raise poultry without affecting the environment. Aquaculture is agriculture, it just happens to be done in the water. Terrestrial agriculture got thousands of years to perfect itself; in the sea we're having to do it in a few decades."