The late-nineteenth-century revolution in sea fishing put wild fish stocks under intense pressure again and stimulated the first aquaculture experiments with plaice and turbot. As with salmon, these efforts concentrated on spawning fish in captivity to supplement wild populations with large-scale releases of young fish. Marcel Herubel captured the spirit of these pioneering efforts in 1912:11
Piscifacture may legitimately claim to be of social value. It goes further than pisciculture, which limits itself to rearing fish; it endeavors to “manufacture” fish. The first art is a nurse, the second a mother.… Piscifacture will restore to the sea what it would have produced had man not multiplied his catches.12
For fairly obvious reasons, these well-meaning attempts ended in failure. Juvenile fish suffer extremely high mortality rates in the wild, and few reached adulthood. Even the release of millions of young fish had little impact on the numbers that eventually found their way into fishing nets, especially since captive-reared juveniles tend to be less fit than their wild-spawned brethren. So the direction of aquaculture shifted.13 A parallel development concentrated on raising wild- spawned animals in captivity from egg to adult. A third strand saw the refinement of methods to raise shellfish such as oysters and mussels. Shellfish mariculture has ancient origins. In the Broughton Archipelago of British Columbia, First Nations people erected rock walls across bays to trap sand to the depths favored by clams, which were an important winter food.14 Nobody is sure when these walls were first built, but they may go back five thousand years and show just one of the many ways these people transcended the simple hunter-gatherer stereotype to nurture nature to support their needs.
In less than a century aquaculture has evolved from a frustrating practice pursued by mavericks into a highly successful international business. From 1950 onwards, when the FAO began to collect statistics, aquaculture production has expanded from less than one million tons a year to more than fifty-five million tons, just over half of which is from freshwater fish like carp and tilapia. To that we can add another eighteen million tons of seaweed. The growth of aquaculture has outpaced every other form of food production in the last decade or two, except organic (which is rising fast from a low base). Since 1950, it has increased at three times the rate of growth in world meat production, and even outpaced world population growth. So when aquaculture is included, the total amount of fish available to eat per week has risen from 6.9 ounces to 7.2 ounces per person, better than the picture from wild fish catches alone but still a fifth less than the average of health recommendations. Unfortunately, about a third of wild catches are fed to livestock, pets, and aquaculture, leaving just 5.6 ounces per person per week to eat.
While nearly four hundred different species of fish and shellfish are cultivated, a handful dominates production. On the marine side, the major players are mussels, clams, and prawns. Shellfish are cultured all over the world, mainly on ropes strung across bays and mud flats in operations that can cover tens of square miles. Mussels and clams are the mainstays of these farms, but even free-living mollusks like scallops are grown on ropes in bags.
Atlantic salmon is the species most Western consumers associate with aquaculture, but in 2008 salmon farms produced over 1.5 million tons of fish, only about a twelfth of the volume of mollusks and prawns sold that year. Salmon are joined in the top ten farmed fish by a cast of lesser characters, including rainbow trout, seabream, sea bass, Japanese amberjack, barramundi, and the unfortunately named bastard halibut, whose forename is usually dropped by supermarkets! But other highly lucrative species are also now farmed, such as bluefin tuna, groupers, and sturgeon.
In 2008, four out of five fish eaten in China were raised in farms. Outside China, one in four fish eaten was farmed, up from one in twenty in 1970. It seems that there is hardly a sea loch or fjord in the developed world that does not support, or is not earmarked for, aquaculture. There are parts of Japan and China where you can stand on the beach and see nothing but fish pens or seaweed strings all the way to the horizon. In terms of food production, aquaculture has been the roaring success of recent times. Putting that aside, the industry has many problems. Some are acknowledged even by its most enthusiastic advocates, but others have long lurked in the background and have only recently begun to cause concern.
While filter feeders such as shellfish can feed themselves, the awkward fact is that farmed fish must be fed, and many of the species most prized by consumers in developed nations, like salmon, sea bass, or tuna, eat flesh. People often think of fish farming in terms they are familiar with from the cultivation of cattle or sheep. We raise animals to convert things we can’t eat, like grass, into things we can. But this simple logic doesn’t apply to aquaculture of predatory fish, which happen to be the ones most Western consumers like best, because they are large and tasty with firm, succulent meat. While some freshwater fish such as carp and tilapia eat a largely vegetarian diet, almost all of the marine fish raised in farms are predators. So it is that we must catch wild fish to feed to captive ones, mainly so-called “forage fish,” like anchovies, capelin, herring, and menhaden that live in large schools. These animals would make perfectly good food for us if we ate them directly rather than passing them through salmon or sea bass first. Here, then, is the first of many controversial aspects of fish farming: It can sometimes take several pounds of wild-caught fish to produce just one pound of farmed fish.15
Several of the species we farm are ferocious predators and come from very high in the food chain. Bluefin tuna are caught as juveniles in Australia and the Mediterranean and then grown to market size in pens, during which time they eat an eye-watering quantity of wild fish, up to twenty times the weight of flesh they produce. You get an idea of the problem by considering the idea of trophic levels. They are a shorthand way of assigning a species’ place in the food chain. Think of them as steps on a ladder that ascends from plants and organic muck at the bottom, to sharp-toothed, beady-eyed carnivores at the top. Plants and detritus are level 1, herbivores and detritus feeders are level 2, meat eaters are level 3, carnivores that eat other meat eaters are level 4. Few food chains go longer than five links because something like 90 percent of the energy passed upward is lost at each step. It gets dissipated sustaining life and producing the next generations. Only about 10 percent builds bodies. This energy loss explains why lions are rare compared to antelope and eagles less abundant than rabbits.
This is a simplified view of a food chain, since it assumes that species occupy just one trophic level. Most animals have a mixed diet, eating foods from more than one rung of the ladder. We can reflect this by giving them intermediate values. Most people eat a mix of meat and vegetables, so the average trophic level of humans is about 3.2. The trophic levels of Atlantic salmon and bluefin tuna are 4.4, which gives them a position on the food web higher than African lions, which come in at less than 4. If you are ever stuck for conversation at a party, you might drop the startling nugget that most domestic cats have a higher trophic level than lions. All that salmon and tuna that Tiddles eats places her well ahead of most big cats in the league of carnivory. Because predators sit much higher in food webs than sheep, goats, or cows, the ratio of what you get back to what you put in is much less favorable.
In the last ten years producers have worked hard to rebalance this equation. Across the industry as a whole, the ratio of wild fish going in to farmed fish coming out has fallen from roughly 1:1 to 0.63:1 (excluding species like mussels that feed themselves from the water).16 Mostly their motivation is profit rather than concern for the environment, although there are refreshing exceptions. Fishmeal and oil from wild sources is expensive, and prices have risen faster than inflation as demand has grown. About half of the fishmeal and nearly all the fish oil produced globally is now consumed by aquaculture (the rest goes to pigs, hens, and even cows). Since wild fish catches have leveled off, aquaculture will likely swallow all the world’s fishmeal by 2050, if not sooner. Those who can squeeze more fish out for every on
e put in gain a powerful kick to their bottom line. And while there have been improvements in feed conversion ratios, for some species the figures remain bad. Because of the high fish oil content of salmon feed, pressed out of animals like anchoveta, salmon still average about five pounds of wild fish to produce one pound of farmed.
There are several substitutes for wild fish flesh in aquaculture feeds. Some manufacturers blend scraps from processed fish into their feeds, but their oil content is low so it is only an answer for some farmers. Others grow marine worms for fish to eat. The most widely used substitutes are protein and oils from plants, such as soy and canola. The problem is there is a limit to how much plant matter a carnivore can take before its health suffers, and of more immediate concern to consumers, its taste. Moreover, the much vaunted health benefits of eating fish stem from their content of omega-3 oils. There have been many claims over the years about the wonders of fish oil, including that they reduce cholesterol, protect the heart, sharpen the mind, ease depression, lubricate the joints, improve vision, prevent Alzheimer’s, and on and on. The protective effects on the heart are well accepted, although many other presumed benefits remain unproven. Omega-3 oils are produced only by aquatic plants, so feeding terrestrial plant substitutes to farmed fish will rob them of their health food cachet. The German agrochemicals giant BASF has an answer in the form of canola plants that have been genetically modified to produce marine oils. These plants have been approved in the United States, but many people remain wary of genetic manipulation, so this alternative is unlikely to satisfy all.
In some places, the struggle to find enough fish to feed aquaculture and farming has taken a troubling turn. Bottom-trawl fisheries can have fiendishly high rates of bycatch of unwanted species, most of which are thrown away dead. In India and Venezuela, a new use has been found for this bycatch.17 Instead of being chucked over the side, it is dried and converted to fishmeal that then goes to chicken farms and aquaculture. At first this seems like a good idea, but it can keep trawling profitable long after the practice has driven the original, high-value target animals to economic extinction. The one last check on a fishery, which might spare an ocean habitat from being completely destroyed by overfishing, is its inability to turn a profit. If every scrap of life brought up in the trawl can be sold, then the trawlers will continue to drag their nets until there is nothing left at all.
Not all farmed marine fish are as predatory as salmon or tuna, and many shellfish eat plankton, plants, or detritus. Nonetheless, finfish culture consumes more than one pound of wild fish for every pound produced, and across the board, aquaculture swallows two-thirds as much wild fish as it produces. Hardly a solution, then, to problems of overfishing. Why don’t we just eat the wild fish directly? This is exactly what many people, celebrity chefs included, have tried to encourage. The main ingredients of fish meal are animals like anchovies, sardines, sprats, herring, and blue whiting, fish whose flesh simply drips healthy oil. The problem is that most are small and therefore fiddly, inconvenient, and full of fine bones that wedge between your teeth or catch in your throat on the way down. In a world of ready meals and convenience foods in developed countries it is hard to persuade people to get intimate with heads, tails, and slime when the alternatives are plump, bone-free fillets from farmed stock. Supermarkets love farmed fish too, because they can guarantee supplies of even-size, uniform quality fish fillets no matter what the season or weather. Farmed fish are definitely here to stay.
There is concern that fishing for “forage” fish to sustain Western appetites for predatory fish robs the world’s poor of their staple diet. These small fish made up over half of the fish protein eaten in a sample of thirty-six developing countries from Africa, Asia, and other parts of the world.18 In something like half of African nations, fish protein makes up a quarter to over a half of the total animal protein eaten. Industrial fishing by other countries in African waters under access agreements threatens fish supplies and has already driven up demand for bushmeat, to the detriment of wildlife on land.19
One alternative to these fish is krill, a finger-sized, bright carmine shrimp that lives in polar seas. Estimates suggest that Antarctic waters harbor enough krill to sustain all of the world’s aquaculture with little difficulty. Already, hundreds of thousands of tons of krill are caught annually to make into fishmeal.20 Nothing is that simple, sadly. Fish, penguins, whales, and seals depend on krill and industrial fishing could harm them if it dents krill stocks. And krill are already on the way down as a result of climate change. Krill survive over the winter by grazing algae attached to the underside of floating ice. If the ice melts, krill supplies will crash.
Aquaculture also suffers problems of husbandry. Farmed fish, like any animals kept at high density, are troubled by diseases and parasites. To combat infection and infestation, most farmers dose animals in ponds and pens with antibiotics, pesticides, and fungicides. Since pens are mostly open to the sea, these chemicals spread pollution far beyond the bounds of farms. Nor are these problems confined to captive fish. Take salmon farms, for example, that are mostly located in estuaries that lead directly to rivers inhabited by wild fish. Adult salmon in the wild rarely come into contact with juveniles, because they either die after spawning or return to sea before the young hatch. Now, young salmon must run a gauntlet of salmon farms on their migration to sea, bringing them into contact with the diseases and parasites afflicting captive adults. Sea lice, for instance, feed on salmon skin and muscle. The lesions they create don’t normally kill adult fish, but they can kill the young who wouldn’t normally have encountered them, at least not in such densities. In recent decades wild salmon runs in rivers that empty past farms have declined to a far greater degree than in those that don’t. Estimates put the fraction of wild salmon smolts killed by sea lice from farms at up to 95 percent in one part of British Columbia.21 In the Atlantic, salmon are ghosts of their former abundance in the wild, so such killing rates could wipe them out entirely. Since each river has its own salmon stock that has adapted to local conditions, every disappearance is a step on the road to extinction.
Farmed animals suffer from more aggressive illnesses than their wild brethren. These diseases have emerged as a result of the unnaturally high densities at which animals are kept, and their prevalence is encouraged by stressful conditions within pens and genetic uniformity of the stock. Infectious salmon anemia seems to be a new strain of a virus closely allied to influenza that has adapted to exploit the high densities of susceptible fish in salmon farms.22 Before the advent of pen culture, there had only been a single report of this virus in the wild. When an outbreak occurs it sweeps through captive fish and many countries now require all the fish in affected farms to be destroyed. Ironically, the industry itself has been the main vector for disease spread. Outbreaks in Scotland in the 1990s were closely linked to visits between farms by boats that carried salmon stock.
Infectious salmon anemia can be carried by fish that have recovered from the worst effects of the illness. It can also be transferred from fish to fish by sea lice, which raises serious concerns for the viability of wild fish stocks that have come into contact with infected farms. The disease has now spread to the United States, Canada, and Chile. It was first detected in Chile in 2007, and at the time of writing had halved Atlantic salmon production there.
In shrimps, another disease has jumped from pond to pond all the way across the Pacific. White spot syndrome virus emerged in China in the 1990s, then spread to Japan and Southeast Asia. Affected shrimps become lethargic and discolored, but in truth there is hardly time to notice these symptoms since the virus can kill the entire stock of an affected farm within a few days. By the mid-1990s, the virus had nearly eliminated Chinese shrimp output, and by the late 1990s, it had made it to North and South America. Amid all the death and destruction, white spot syndrome virus has at least had one positive effect. Before the disease emerged, shrimp farming often relied on capture of wild juveniles to stock the pens. Now the indu
stry has mainly moved to spawning its own shrimps from certified disease-free broodstock. Pens also used to exchange highly polluted water with the open sea, but there has been a shift toward greater separation between pens and the sea to minimize possible spread of infection.
Isolation of farms from the open sea is a good idea for many reasons. When faced with disease, farmers have three choices: prevent, treat, or risk losing it all. Options to prevent disease include vaccination, prophylaxis, or disinfection. Vaccination is clean and clinical but only available for a few species and diseases, and often only in developed countries. Prophylaxis usually involves feeding animals antibiotics, while disinfection can mean dosing ponds with toxic compounds such as malachite green, which is known to cause cancer in people. There is growing disquiet about the use of antibiotics in aquaculture. Chile uses over one hundred tons of quinolones every year, mostly on fish farms.23 These antibiotics are important in human medicine, but such heavy use risks the development of antibiotic resistance in microbes. Bacteria tested from sediment and water samples near fish and shrimp farms have begun to develop such resistance, and some can shrug off several antibiotics at once.
You might think that there is little chance of marine bugs causing trouble for us, but bacteria are able to swap genetic material, and genes for resistance have already made the leap from sea to land, and from bugs that affect animals to ones that infect people. A cholera outbreak in South America in the 1990s was of a strain that had picked up antibiotic resistance from contact with a bacterium that owed its enhanced resistance to the heavy use of drugs in Ecuadorian shrimp farms. The sometimes fatal gut bacterium E. coli has also acquired antibiotic resistance via aquaculture. For some human pathogens, exposure to antibiotics in aquaculture can be direct. Asian carp ponds are often praised as a model of sustainability because they raise fish that eat vegetables, dirt, or insects, and they recycle human wastes. In Vietnam, some cities rely on vast aquaculture complexes to treat their sewage, which might give you pause the next time you spot some plump fillets of basa, a type of catfish, in the supermarket.24 So human pathogens swirl around ponds where they can gain antibiotic resistance before being passed back to us when fish are harvested.
The Ocean of Life Page 27
