Current marine aquaculture conditions deplete seas and oceans of life-supporting nutrients. Find out what changes need to be made in order for marine life to thrive in and out of these fish farms.
The first time water rushed onto your toes, your feet buried in the sand, you couldn’t imagine the magnitude of the ocean or all that it held. In Callum Roberts’ vibrant book, The Ocean of Life (Viking, 2012), take a fascinating tour of the history of mankind’s relationship to the sea, from the course of currents first discovered by Benjamin Franklin to the effects of shrimp farming in present-day China. In the last 20 years we have transformed the oceans beyond recognition — and not for the better. Find out how current marine aquaculture conditions harm coastal ecosystems and what we can do to prevent further damage. This excerpt is taken from Chapter 16, “Farming the Sea.”
The explosion of marine fish farms across the world has transformed coasts, estuaries, and deltas in dozens of countries. China has pursued one of the most aggressive aquaculture development programs of recent years. In 2003, marine aquaculture covered nearly six thousand square miles, about half of China’s twenty-thousand-mile coastline. Most of these farms were carved out of mangrove forests, mud flats, salt marshes, and sea grass beds. Satellite photographs of the Bohai Sea coast, one of the most intensively farmed regions, show the toll taken. Straight-edged ponds incised in blue and turquoise pack the coast to depths of a couple of miles inland, and crawl seaward across mud flats. The Philippines and Vietnam have lost three quarters of their mangrove forests in the last few decades, half of them to aquaculture. Sadly, many of these ponds have been abandoned. When mangrove soils are exposed to the air, they become acidic. The acid leaches into pond water together with toxic quantities of aluminum, so the ponds cannot be used unless they are lined.
Mangroves and salt marshes are self-repairing buffers that defend coasts against storm and flood. If they remain healthy, there is a good chance they could also ameliorate the worst effects of sea-level rise by trapping sediment and building upward. In many places aquaculture has not only removed this benefit, it has caused the land to sink by sucking freshwater from belowground to create brackish ponds for shrimp and milkfish.
Ironically, the loss of these habitats starves fish farms of two things they need most: clean water and animals to stock their ponds. Coastal wetlands draw nutrients and pollution from the water that washes through them. They are also nurseries for a huge variety of fish and shellfish. Although disease has forced many shrimp farmers to switch to hatchery-raised fry, countless farms throughout the tropics still depend on wild sources to stock their ponds, despite its catastrophic environmental cost.
Tiger prawns are much favored for their large size and rapid growth, but they represent a tiny fraction of wild shrimp fry. Most wild prawn fry are caught by night lighting in shallow water under a moonless sky. Within minutes, netters are surrounded by a confusing buzz of hundreds or thousands of tiny animals, fish and fry, all drawn to the light like moths to a flame. For every individual tiger prawn caught in Malaysia and the Philippines, several hundred fry of other species are wasted. Half of the hundreds of millions of tiger prawns grown in Bangladesh are from the wild. The waste doesn’t stop at other shrimp species either. In one study, scientists found that every tiger prawn fry collected cost the lives of up to hundreds of finfish fry and over a thousand other animals that live in the plankton.
The wetland grab in developing countries has robbed the poor of the common lands from which they once eked a living by fishing and gleaning. Aquaculture provides jobs and income for some of the displaced. But the divide between rich and poor has grown, and their quality of life suffers with every waterway blocked, every forest tree felled, and every pint of pond sludge pumped into the sea. In several countries, such as Bangladesh, Thailand, and Honduras, some of those bold enough to protest the injustices have been murdered to quash opposition.
So far marine aquaculture has sheltered most of us from the effects of overfishing. Throughout the developed world supermarket shelves creak under the weight of an ever expanding range of farmed fish and shellfish. There is something for everyone if you can afford to pay: sturgeon caviar, bluefin tuna sashimi, and oysters on the half shell tempt high-end diners, while there are salmon and shrimp for the masses. And yet, the amazing expansion of fish farming since 1950 has come at a terrible cost to coasts, wetlands, and shallow seas. Governments hell-bent on foreign exchange or job creation have encouraged aquaculture heedless of warnings. It is not hard to see that it can’t go on like this.
The drawbacks of aquaculture are such that one might question whether it really is the solution to overfishing. Wouldn’t it be better to protect fish in their natural habitat? If we were to manage wild fisheries well, we might be able to increase supplies from the open sea by a third to a half. But a 50 percent increase falls far short of the needs of nine billion hungry people expected by 2050. So if the world aspires to a healthy diet of fish, aquaculture will be essential. Like any kind of farming, there are better and worse ways of doing it. The present blue revolution will need to turn blue-green for aquaculture to become a net contributor to human well-being. What would it take to do this?
Better farming practice comes in many forms. In some countries, shrimps are grown in ponds at low enough densities that nature can feed them without the need for supplementary food. But such ponds take up more space than intensive farms, at a greater cost to wetlands and coastal ecosystems. In the Philippines, the value of mangrove forests is now becoming recognized thanks to the tireless campaigning of scientist and activist Jurgenne Primavera. She says, based on decades of research, that shrimp ponds should not exceed a quarter of the area of mangrove forest if we are to preserve the ecological function of coasts. Her work has led efforts to restore forests and move ponds behind sheltering buffers of trees, and she was hailed a hero of the environment by Time magazine in 2008. (Shellfish and seaweeds can also be cultured in natural mangrove and salt-marsh channels.) At the other end of the spectrum, experimental farms in Belize have gone for high-technology, superintensive methods. Their shrimps are raised under covered raceways and fed on biofloc, clumps of microbes formed around starch grains and sprinkled into the water. This reduces the need for expensive feed and helps recycle nutrients from shrimp excreta, which reduces sludge production.
We may need to say good-bye to the succulent predators favored by Western consumers and rich Asians alike. Marine aquaculture will have to learn instead from the ancient art of carp polyculture practiced in the freshwater ponds and rice paddies of Asia. We need to find species that grow well together so that one will clean up the waste produced by another. Some fish eat seaweed or detritus and can be raised more sustainably than those that crave fish flesh. Mullet grub around on the seabed for their food and might reduce pollution problems if farmed together with more predatory fish. Likewise, sea cucumbers are considered a delicacy throughout much of Southeast Asia and have been seriously overfished in the wild. These animals are a bit like vacuum cleaners with a hole at one end where detritus goes in and a bum at the other where something that looks nearly identical comes out. Years ago, before I was aware of seafood problems, I tasted sea cucumber soup. I have to admit I’m no connoisseur and it felt a bit like chewing on a rubber band. But the Chinese and Japanese love sea cucumbers and it could make sense to grow them beneath pens of fish to help recycle their waste.
The industry will need to work hard to raise standards and improve sustainability. I have met many fish farmers who are committed to doing just that. With their energy and enthusiasm, aquaculture could indeed help feed the world. But there are challenges ahead. Growing shellfish has always been touted as one of the most environmentally friendly ways to produce seafood. Mussels, clams, and scallops feed on plankton and other organic matter filtered from the water around them. They don’t need to be fed wild-caught fish and can improve water quality. But there is a catch. They depend on their carbonate shells, and life is going to get much tougher for them, and would-be aquaculturists, as the seas become more acidic. If you are fond of mussels and scallops, you may want to think hard about what we can do to reduce carbon dioxide emissions.
This excerpt has been reprinted with permission from The Ocean of Life: The Fate of Man and the Sea by Callum Roberts, published by Viking, 2012.