Aquaculture

• 1. Introduction

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  Aquaculture moved a staggering 130.9 million tonnes of farmed aquatic life in 2022, worth 312.8 billion US dollars. That figure represents fish, shrimp, oysters, seaweed and more, all raised under human control rather than chased through the open sea. The reach is so vast that one country alone reports an output double that of the rest of the world combined. Yet the numbers carry an asterisk, because the reliability of those reported figures has been questioned for decades. This is the controlled cultivation of aquatic organisms, sometimes called aquafarming, and it stands in contrast to commercial fishing, the harvesting of wild fish. How did a practice that some trace back thousands of years grow into the activity that now feeds more people than wild fishing does? What does it cost the coastlines, the wild fish, and the animals raised inside the cages? And why did one ocean explorer warn, back in 1973, that humanity would have to turn to the sea with new understanding and new technology? The answers begin with how this farming actually happens, on land, near shore, and far out in open water.

• 2. Where The Farming Happens

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  Onshore aquaculture builds completely artificial facilities on land, including fish tanks, ponds, aquaponics setups, and raceways. Inside these systems, humans control the living conditions directly, managing water quality such as oxygen, feed, and temperature. The fish never meet a natural current.

  Inshore aquaculture works on well-sheltered shallow waters near the edge of a body of water. Here the cultivated species face relatively more naturalistic environments than they would in a tank on land. The setting is sheltered, but no longer fully artificial.

  Offshore aquaculture pushes farther out, onto fenced or enclosed sections of open water away from the shore. Species there live in cages, racks, or bags, exposed to diverse natural conditions like water currents, diel vertical migration, and nutrient cycles. Mariculture, commonly known as marine farming, covers all cultivation in seawater habitats and lagoons, as opposed to freshwater aquaculture. Channel catfish, hard clams, and Atlantic salmon are prominent in United States mariculture, each raised by methods suited to its needs.

• 3. The Blue Revolution

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  Jacques Cousteau, writing in 1973, captured the mood of early modern aquaculture when he urged that growing human populations would force people to turn to the sea. Harvest stagnation in wild fisheries and overexploitation of popular marine species had collided with rising demand for high-quality protein. Many were optimistic that a "Blue Revolution" could transform aquaculture the way the Green Revolution had transformed agriculture in the 20th century.

  About 430 of the species cultured, roughly 97 percent, were domesticated during the 20th and 21st centuries, with an estimated 106 arriving in the decade to 2007. The contrast with land farming is sharp. Only 0.08 percent of known land plant species and 0.0002 percent of known land animal species have been domesticated, compared with 0.17 percent of known marine plant species and 0.13 percent of known marine animal species.

  Domesticating aquatic species carries fewer risks to humans than domesticating land animals did. Most major human diseases, including smallpox and diphtheria, originated in domesticated land animals and moved to humans from them. No human pathogens of comparable virulence have yet emerged from marine species, a quiet advantage of farming creatures so distant from our own biology.

• 4. The Species On The Menu

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  Carp, salmon, tilapia, and catfish are, in that order, the most important fish species used in fish farming worldwide. Fish farming is the most common form of aquaculture, raising fish in tanks, ponds, or ocean enclosures, usually for food. A facility that instead releases juvenile fish into the wild for recreational fishing is called a fish hatchery.

  Young bluefin tuna in the Mediterranean are netted at sea and towed slowly toward the shore, then interned in offshore pens, sometimes built from floating HDPE pipe, to grow for the market. In 2009, researchers in Australia coaxed southern bluefin tuna to breed in landlocked tanks for the first time. The same species is also fattened in grow-out sea cages in southern Spencer Gulf, South Australia.

  Commercial shrimp farming began in the 1970s and grew steeply, reaching more than 1.6 million tonnes in 2003, worth about 9 billion US dollars. Around 75 percent of farmed shrimp comes from Asia, especially China and Thailand, while Brazil is the largest producer in Latin America and Thailand is the largest exporter. Just two species, the Pacific white shrimp and the giant tiger prawn, account for roughly 80 percent of all farmed shrimp. These industrial monocultures are very susceptible to disease, which has wiped out shrimp populations across entire regions.

  Aquacultured shellfish include oyster, mussel, and clam species, all bivalves that filter or deposit feed on ambient production rather than added feed. For that reason shellfish aquaculture is generally seen as benign or even beneficial. In May 2017 a Belgian consortium installed the first of two trial mussel farms on a wind farm in the North Sea.

• 5. Ranching The Reef

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  Brad Adams put it plainly: "We're not aquaculture, we're ranching, because once they're in the water they look after themselves." His company set up a commercial sea ranch in Flinders Bay, Western Australia, after trials in 2012, to raise abalone. The whole operation rests on an artificial reef.

  The reef is made of 5000 separate concrete units called abitats, short for abalone habitats. Each 900 kilogram abitat can host 400 abalone, seeded as young animals from an onshore hatchery. The abalone feed on seaweed that grows naturally on the habitats.

  The enrichment of the bay spread far beyond the abalone themselves. Growing numbers of dhufish, pink snapper, wrasse, and Samson fish appeared among other species, drawn to the new structure. Abalone farming had begun in Japan and China in the late 1950s and early 1960s, and after overfishing and poaching reduced wild populations, farmed abalone now supplies most abalone meat.

• 6. The Hidden Cost To Wild Fish

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  Several kilograms of wild fish go into producing a single kilogram of a piscivorous farmed fish like salmon. This is measured as the fish-in-fish-out ratio. In 1995, salmon had a ratio of 7.5, meaning 7.5 kilograms of wild fish feed were required to make one kilogram of salmon; by 2006 the ratio had fallen to 4.9.

  Fish do not produce omega-3 fatty acids themselves. They accumulate them from microalgae, either directly, as forage fish like herring and sardines do, or indirectly, as salmon do by eating prey fish. To satisfy this need, more than 50 percent of the world's fish oil production is fed to farmed salmon.

  Seventy-five percent of the world's monitored fisheries are already near or beyond their maximum sustainable yield, even as the salmon industry demands more forage fish. One answer has been to shift carnivorous species onto plant-based feeds. Salmon feeds have gone from containing only fishmeal and oil to containing 40 percent plant protein, and the United States Department of Agriculture has experimented with grain-based feeds for farmed trout. A growing share of fish oil and fishmeal now comes from residues, the byproducts of fish processing, with 34 percent of fish oil and 28 percent of fishmeal sourced that way in 2012.

• 7. What It Does To The Water

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  A farm with 200,000 salmon discharges more fecal waste than a city of 60,000 people, released directly into surrounding waters, untreated, often carrying antibiotics and pesticides. Salmon farms are typically sited in pristine coastal ecosystems that they then pollute. Heavy metals, particularly copper and zinc, accumulate on the seafloor near them.

  About 20 percent of mangrove forests have been destroyed since 1980, partly because of shrimp farming. Over four decades, 269,000 hectares of Indonesian mangroves were converted to shrimp farms, and most of those farms were abandoned within a decade because of toxin build-up and nutrient loss. An extended cost-benefit analysis of shrimp aquaculture built on mangroves found the external costs far higher than the external benefits.

  Whole-lake experiments at the Experimental Lakes Area in Ontario, Canada, revealed how cage farming reshapes freshwater. After an experimental rainbow trout cage farm started in a small boreal lake, mysis concentrations dropped sharply alongside falling dissolved oxygen. Ammonium and total phosphorus rose in the hypolimnion, and phytoplankton biomass quadrupled each year after the farm began.

  Not all forms harm the water. A single oyster can filter 15 gallons a day, removing microscopic algal cells and the nitrogen bound up in them. One study estimated that 10 square meters of oyster reef could enhance an ecosystem's biomass by 2.57 kilograms. Seaweed farming is a carbon negative crop, singled out by the IPCC Special Report on the Ocean and Cryosphere in a Changing Climate as deserving further research attention as a climate mitigation tactic.

• 8. The China Question

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  China reports a total aquaculture output double that of the rest of the world combined, dominating the global figures so thoroughly that any error there distorts the whole picture. Between 1980 and 1997, the Chinese Bureau of Fisheries reports, aquaculture harvests grew at an annual rate of 16.7 percent, jumping from 1.9 million tonnes to nearly 23 million tonnes. By 2005, China accounted for 70 percent of world production.

  In 2001, scientists Reg Watson and Daniel Pauly raised concerns that China had been over-reporting its wild fishery catch in the 1990s. They calculated that the data made the global catch since 1988 appear to grow by 300,000 tonnes annually, when it was actually shrinking by 350,000 tonnes a year. They suggested this traced to Chinese policies under which state entities that monitored the economy were also tasked with increasing output, and officials were promoted based on production increases from their own areas.

  China disputed the claim. The official Xinhua News Agency quoted Yang Jian, director general of the Agriculture Ministry's Bureau of Fisheries, who said China's figures were "basically correct". The Food and Agriculture Organization, however, accepted there were reliability issues and for a period treated data from China, including its aquaculture data, separately from the rest of the world. That decision reaches back across the centuries to the oldest roots of the practice, including oral tradition in China telling of common carp culture as long ago as 2000 to 2100 BCE.