Many developed countries have recognized the dangers of antibiotics and have banned their use. In Norway, most salmon are vaccinated against problem infections. Things that happen in Asia or South America or Africa can seem comfortingly remote to many of us. But this is a globalized world and what happens in one place soon spreads to others, as outbreaks of bird and swine flu show. More than 90 percent of world aquaculture production comes from developing countries, so until the problems are solved there, little progress has been made. In Asia, where most of the world’s farmed fish are grown, farms routinely use industrial quantities of antibiotics, pesticides, disinfectants, and antifungals.
Toxic chemicals released to the sea are a worry, but they highlight another of the ways in which aquaculture does damage. Where pens exchange water with the open sea, as most do, the wastes from excess food and feces simply washes away. If there are few farms and plenty of water to slosh past them, we might see little impact and easily live with the consequences. But farms are often put in sheltered bays, estuaries, and fjords where water exchange is limited, and the growth of fish farming means that some places are packed with pens, each of which can contain tens or hundreds of thousands of animals. That adds up to a huge amount of waste. By 2000, Scotland’s salmon farms released as much nitrogen—one of the main fertilizing nutrients that fuel plankton blooms—as is contained in the untreated sewage of 3.2 million people, over 60 percent of Scotland’s population.25 Output of phosphorus, the other major plant nutrient, was equivalent to the waste produced by 9.4 million people. In the early years of the twenty-first century, Chinese shrimp ponds released forty-seven billion tons of effluent into coastal seas, compared to over four billion tons of industrial effluent and sewage from land-based sources.26 Shrimp farms produce mind-boggling amounts of nutrient-rich sludge: in intensive culture, tens to hundreds of tons per hectare for every shrimp crop.27 These farms have doubtless played a critical role in the problems of oxygen depletion, harmful algal blooms, and fish kills that have plagued regions like China’s Bohai Sea. Blooms in China now affect an area bigger than the Mississippi dead zone. Toxic algae provide a strong motivation to find cleaner ways to farm fish, since they can wipe out stocks and profits within hours when they strike. In Philippine bays so crowded with cages and pens there scarcely seems any open water, since 1999 yearly mass kills of milkfish and tilapia have destroyed hundreds of thousands of tons of stock. Such problems not only threaten production, they pose real health concerns to consumers.
If the Bohai Sea is not the most polluted sea on the planet, it must be close. It lies downstream of the heartland of the Chinese economic miracle. This transformation of fortunes, like the past Industrial Revolutions of Europe and America, has been bought at the price of severe pollution. Industrial effluents mingle with sewage discharges from tens of millions of homes. Maps produced by the Chinese government show almost every part of the Bohai coast suffers from excessive levels of contaminants like lead, chromium, mercury, and arsenic alongside the fertilizing nutrients.28 Off the city of Tianjin, water quality is so bad that most falls into the pollution category of “offensive in color, smell, and taste.” This pollution threatens the burgeoning aquaculture industry. So filthy has the water become that there is widespread use of antifungal and antibacterial compounds to keep the animals alive, like nitrofuran, a known carcinogen banned throughout much of the Western world. So farmed animals are contaminated in multiple ways—with DDT, flame retardants, and mercury from the water, and with prophlylactic chemicals applied by farmers. As China has become a major exporter of farmed fish and prawns, these problems are a concern for consumers far beyond the shores of the Bohai.
In previous chapters I talked about how aquaculture has contributed to the spread of invasive species and diseases around the world. This “biological pollution” is considered by some to be among the worst effects of fish farming, because it is usually irreversible by the time the problem is noticed. Atlantic salmon have already established themselves in several rivers in British Columbia. Huge Pacific oysters, three times the size of man’s hand, are now embedded in northern European seas after they were introduced to replace native oysters. In the Gulf of Maine, imports of European oysters probably brought in the invasive seasquirts and fingerlike Codium, a vibrant green seaweed, that competes aggressively for space with native fauna. No one knows how these or hundreds of other alien species incubating in new environments will turn out; some will definitely go rogue. But there is another form of release that is just as irreversible and scares some people even more: the use of genetically modified fish.
Like any form of farming, aquaculture has its high technology enthusiasts who can spot ways to make better animals. At the time of writing (2011), the first transgenic salmon was nearing approval in the United States.29 Called Aquadvantage, this Atlantic salmon has been given a chinook salmon growth hormone gene, and another from ocean pout that prevents the growth hormone from being switched off in winter. So these fish pile on weight year-round to reach market size twice as fast as normal salmon. Protesters argue that escaped animals will interbreed with wild and set free Frankenstein fish. But the company that makes them says it is highly unlikely, since 99 percent of fish have an extra copy of the salmon genome to ensure infertility, and they will be grown in closed containers on land. Protesters do have a point, though, since reassurances from the biotech industry have several times proved less robust than claimed. In any case, this salmon will have to clear regulatory hurdles outside the United States to gain a foothold on the market since most salmon farming is in Canada, Chile, and Europe. But despite passionate resistance among environmentalists, it seems inevitable that in the long run aquaculture will embrace genetically engineered fish.
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.30 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 hun
dred 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.31
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 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. (I will come back later to how we can do this.) 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 2008.32 (Shellfish and seaweeds can be 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. There 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.
CHAPTER 17
The Great Cleanup
There is an old adage that “dilution is the solution to pollution.” Follow that logic, and you would think that there is no better place to dispose of waste than in the sea. But even the sea can reach saturation. Over the last twenty years, estuaries, bays, gulfs, and enclosed seas have been overwhelmed by the volume and variety of waste, both of the kinds you can see, like plastic, and the kinds you can’t, like toxic chemicals and fertilizers.
In the past nature could be relied on to cleanse our effluents as they passed through coastal marsh and mangrove. Once at sea they were filtered out by the gaping mouths of millions of suspension feeders that packed the seabed or swam in shoals so large they darkened the water for tens or hundreds of miles. But as the sea has been stripped of its consumers, and its coasts cleared of the wetlands that once lined creeks and waterways, so its power to regenerate waste has waned. Dilution is no longer the solution. Today the emphasis in pollution control must swing to reduction, prevention, and, in some cases, removal.
For persistent pollutants like heavy metals and PCBs, reduction and prevention are essential. There has been some progress over the last two decades, but past generations have left us a toxic legacy that we must pay for and every year we are adding more. In Europe and North America bans have long been imposed on the use of the most toxic and lingering compounds like PCBs and organochlorine pesticides like DDT. These measures have begun to reduce the burden of pollutants in the Baltic Sea and the Gulf of Maine, but DDT and its toxic breakdown products are still with us and these bans will have limited global impact until all of the developing world follows suit. Left to their own devices many of these chemicals bind to particles of silt and clay suspended in the water. When sediments sink to the bottom the toxins are buried, and in an ideal world that is where they would stay. Unfortunately, storms and tides mix sediments back into the water column and circulate the toxins back into the food web to haunt us again. And there is also a human force mixing mud and its toxic hitchhikers back into the water: bottom trawling and dredging.
It amazes me that more has not been made of the way that trawlers and dredgers kick up mud from the seabed. Trawlers fishing shallow water are visible from space because of the “contrails” of mud that stream from their nets. The Gulf of Maine is one of the most heavily trawled seas on the planet. Oceanographers have known for years that a thick and permanent layer of suspended mud overlies much of the seabed, but they weren’t sure why it was there. When worms that normally live within seabed sediments showed up in traps set 80 feet above the bottom, the mystery was solved.1 Bottom trawlers churned mud, worms, and pretty much everything else into the water above. Parts of the Gulf of Maine contain high levels of persistent pollutants washed downstream from factories and heavy industry of New England. Here and elsewhere,
trawlers are revisiting upon us the ghosts of chemical industries past.
It seems only recently to have dawned upon many developed nations that the oceans are a common pool shared by all, and that the pollutants released by one nation can swiftly slosh to the shores of another, even thousands of miles away. Plastics are easily seen, but pollutants like mercury or DDT, harder to detect and easily overlooked, have spread to every corner of the globe. Bizarrely, many developed countries still permit companies to manufacture and sell toxic compounds like DDT overseas. DDT itself is permitted for control of mosquitoes that spread malaria, and three to four thousand tons of it are sprayed inside people’s houses in Africa and Asia every year. In India and North Korea, people still use DDT illegally for general agriculture. Malaria is terrible, but can’t we come up with a less toxic alternative?
Like many others, this problem requires a global solution. The Stockholm Convention on Persistent Organic Pollutants came into force in 2004 and at the time of writing 176 of the world’s 195 nations were party to it.2 Currently it commits signatories to eliminate seventeen of the most toxic and accumulative chemicals, and limit production and use of several others, but we still have a long way to go. There are still too many countries where highly toxic pollutants are used and ultimately wash into the sea.
The Ocean of Life Page 28
