Plenty of Fish on the Farm

Why Clean Energy Is Key for Next-Generation Aquaculture

In this essay:

Oceans cover two-thirds of the blue planet, and yet remain largely a mystery to humans. The seas are filled with a dizzying variety of life, but the only marine species most of us see regularly are those that land on our dinner plates. Each year 80 million metric tons of seafood are harvested from the oceans.1 Fish remain one of the last foods that humans hunt from the wild at a commercial scale.

There is clearly a role for well-managed wild fisheries in the global food supply, since they offer a relatively low-input source of high-quality animal protein.2 Ray Hilborn, a prominent fisheries scientist, says, “We should be aiming for 100 percent fully fished wild fisheries as our goal.” That does not mean overfishing, however; “fully fished” means the maximum sustainable yield, where the wild population can regenerate and make up for the harvested fish.

Unfortunately, experts at the UN estimate that almost a third of global fish stocks are indeed overfished—that is, fished at a biologically unsustainable level.3 Wild fisheries, even well-managed ones, simply do not have the potential to meet continued increases in demand for seafood from a larger, wealthier global population. Instead, future demand for the fruits of the sea will be met the same way we satisfy demand for beef and chicken: by farming it.

Read more from our series on The Future of Food.

Aquaculture, or fish farming, is both an ancient tradition and, today, a global commercial industry. From Chinese farmers raising carp in flooded rice fields to intensive salmon farms in Norway’s fjords, fish farming is a diverse and global activity. And today, aquaculture stands poised to dominate the seafood sector. The UN’s Food and Agriculture Organization projects that in the coming decades wild-capture production will remain fairly flat, while aquaculture production will surge, increasing almost 40% in the next ten years.4 Between 1990 and 2009, aquaculture was the fastest growing livestock sector,5 and in 2014, aquaculture surpassed wild capture as our main source of seafood for the first time ever.6

A future where farmed fish play a greater role in global diets is likely one that is better for both land and ocean ecosystems than one without it. Aquaculture is a crucial supplement to wild-capture harvests, and fish are more efficient at converting feed into protein than pigs or cows, so farmed fish generally has lower environmental impacts than meat.7 Of course, all animal protein sources come with environmental impacts, and today’s aquaculture sector generates significant ones. Commercial aquaculture can destroy coastal habitats, generate nitrogen pollution, and put pressure on forage fish stocks—low-value fish that are harvested for aquaculture feeds.8

Almost a third of global fish stocks are fished at a biologically unsustainable level.

The pathway that the aquaculture sector follows in the coming decades will have tremendous impacts on the environment. Changes to aquaculture inputs, especially fish feeds, will improve the environmental performance of fish farming, and a drop-off in demand for carnivorous species like salmon and shrimp would also reduce impacts. However, a sustainable future for aquaculture may also mean radical changes to production methods. Instead of smallholder systems and coastal aquaculture, which dominate the sector today, aquaculture will have to move on land and offshore in order to dramatically reduce its impacts.

Farming fish in recirculating tanks on land or in deep offshore waters can greatly reduce or even eliminate many of the environmental problems plaguing the sector today, including pollution, damage to habitats, and freshwater consumption. However, both also require greater energy consumption than today’s prevailing systems. Indeed, reducing environmental impacts often requires more energy. A sustainable future for aquaculture in the 21st century is thus possible, but it will likely depend on an abundant supply of clean energy, highlighting the centrality of energy in environmental challenges.

From Smallholder Farms to Commercial Exports

Today, the majority of people engaged in fish farming worldwide are smallholder producers,9 mostly in Asia.10 Many of them are engaged in the kind of traditional fish farming that has existed for centuries; in China, for example, farmers have been raising carp in flooded rice paddies dating back 8,000 years, and the practice continues today.11

This type of traditional, extensive aquaculture involves stocking fish in small ponds or nets in ponds, rivers, and reservoirs. Fish feed on natural food—plankton in the water or worms and snails from sediment.12 Very few external inputs are used, although farmers may fertilize the water with animal or human waste to enhance natural food production in the water.13 Productivity levels are usually quite low—less than one metric ton of fish per hectare per year14—and the fish are used for household subsistence or local consumption, rather than commercial sale or export.15

These low-input systems can be relatively environmentally harmless.16 The fish farms are typically integrated with natural bodies of water like lakes or reservoirs, so there is no pumping of freshwater to create an artificial aquaculture environment. Since they rely mainly on human labor, there is also very little or no industrial energy consumption. By not using external feeds, extensive fish farms also save on costs and environmental impacts.

Extensive fish farming can still generate pollution and habitat impacts, however.17 Creating artificial ponds can alter the natural landscape, and waste from farmed fish can change the nutrient profile in natural bodies of water, impacting other aquatic life. However, since extensive fish farming uses only minimal fertilization and no external feeds, nutrient pollution is not as much of a concern as with larger-scale, more commercial operations.18

Despite being relatively benign environmentally, small-scale aquaculture is not equipped to meet rising commercial demand for seafood. Without using external feeds, natural food availability limits the scale of production on a given fish farm.19 To increase output, more bodies of water could perhaps be brought into use, but this would expand impacts on the landscape and would not resolve the problem of low area productivity. Rural aquaculture has also not proven a reliable way for families to emerge out of poverty,20 and increasing urbanization has led many small-scale farming households to abandon aquaculture and seek off-farm employment in cities.21

Milkfish farming is a centuries-old industry in Indonesia, the Philippines, and Taiwan. Slow to modernize, it now faces challenges from competing aquaculture species and as a result of present economic realities.

Given the low productivity of extensive fish farming, supplemental feeds have been necessary to farm enough fish to meet growing demand. Today, aquaculture that uses external feeds already represents the majority of farmed fish production, and its share is growing.22 Many areas formerly dominated by rural aquaculture have transformed into centers for export-oriented commercial production.23 The Mekong Delta in Vietnam, for example, has undergone rapid intensification, transforming a sector dominated by smallholders into a global aquaculture producer and exporter.24

Most commercial aquaculture today can be characterized as semi-intensive, meaning farmers use external inputs but the fish farm is still an open system. Many commercial operations farm fish in net pens in the ocean or in a pond or lake, while in other types of inland operations, water is cycled into artificial ponds and raceways from a nearby water source. Farmers use commercial feeds and fertilizers to boost fish growth, they culture higher-value, selectively bred species of fish, and they sell their final product commercially, often for export.25

The management practices in semi-intensive systems increase productivity, but these fish farms are still interconnected with the surrounding environment. This can create a dangerous combination of intensive production in the middle of natural ecosystems. The open aquaculture systems that dominate commercial production today can produce direct environmental impacts in the form of habitat loss, pollution, and freshwater consumption.26 Open aquaculture systems often depend on being located in sensitive coastal ecosystems where the conditions are right for aquaculture, linking fish farming to immediate environmental impacts.

One of the most well-known examples of habitat loss from commercial aquaculture is the destruction of mangrove forests in Southeast Asia. Beginning in the 1960s and ’70s, governments in Southeast Asia encouraged smallholder farmers to convert mangrove forests to shrimp farms to promote economic development and food production.27 A review study found that between 2000 and 2012, aquaculture was responsible for about 30 percent of total mangrove loss, or 30,000 hectares.28

Khao Daeng village, Pranburi, Thailand, where shrimp farming and fishery have contributed to the destruction of mangrove forests.

Inland aquaculture can also degrade habitat areas by clearing land to create artificial ponds and raceways and by diverting water from rivers, ponds, and reservoirs, disrupting the aquatic ecosystem.29 In flow-through systems on land, water is sometimes cycled through the aquaculture system and returned to the water source with effluents and waste still present, which can create a pollution problem and trigger eutrophication.30

While coastal aquaculture does not create direct demand for freshwater, it can still cause pollution problems. In marine net pens and cages, fish waste and excess feed can change the nutrient balances in the surrounding waters and disrupt the marine ecosystem. Because commercial fish farms stock fish at higher densities, they also sometimes use hormones and antibiotics to reduce disease and promote fish growth.31 When these compounds are freely exchanging with the surrounding water, it can harm other flora and fauna.32 Commercial salmon farms in Chile33 and Scotland,34 for example, have caused controversies for polluting waterways with pesticides and triggering toxic algae blooms.

There are ways to reduce nutrient pollution in open systems, both with modern technology and more traditional methods. Some modern marine net pen systems use video cameras that detect when uneaten feed begins falling to the bottom of the pen, triggering the feed machines to turn off.35 A more low-tech way to reduce nutrient build-up is using other species to do the job: multi-trophic aquaculture involves farming filter-feeding species like shellfish or seaweed alongside fed species like salmon or shrimp. The byproducts from the fed species become the inputs for the filter feeders, reducing effluent build-up, improving water quality, and generating an additional economic good for producers.36 A study of salmon farms in Chile found that culturing red algae alongside the fish farm can successfully absorb the nitrogen effluents produced by the salmon, although a large area of algae would be needed to eliminate nitrogen pollution entirely.37

The pathway that the aquaculture sector follows in coming decades will have tremendous impacts on the environment.

A source of environmental impacts in any commercial system is feed production, which can generate impacts that dwarf everything that happens on the farm level.38 The feed issue is especially important for carnivorous species like shrimp and salmon, which are given feeds with fish meal and fish oil made from processed wild forage fish.39 This dependence on forage fish ties aquaculture production to wild fisheries.

Feed production is not only an environmental challenge but a high cost for producers as well, so fish farmers have a strong incentive to reduce their demand for expensive fish meal and fish oil.40 One way to do this is improving the feed conversion ratio, or the amount of feed the fish need to reach mature size. More intensive production methods can improve feed conversion ratios because they stock fish at high densities, use fish selectively bred for growth, and carefully control water quality to provide the ideal growing environment.41 These kinds of management interventions have brought down feed conversion ratios for major farmed species like shrimp, tilapia, and salmon by about 25% since the 1990s.42

Convincing consumers to prefer herbivorous fish like tilapia to carnivorous ones like salmon would also help reduce the demand for fishmeal and fish oil. In the meantime, though, producers are tricking carnivorous fish into being omnivores by substituting plant proteins for fishmeal in feeds.43 Feeds with a higher share of plant ingredients have their own agricultural impacts, of course, including fertilizer and water consumption.44 Improvements to crop agriculture will thus also rebound positive effects to the aquaculture industry.

Ultimately, commercial open aquaculture systems will always face environmental challenges since they rely on external inputs to intensify production, but remain integrated with the surrounding environment. Pollution can’t be eliminated entirely when a commercial fish farm is placed in a natural body of water, and habitat loss and degradation will continue to be a problem, especially for coastal aquaculture. Relying on the natural environment to provide the setting for aquaculture can provide advantages for producers, but ultimately ties fish farming to environmental risks as well.

The current state of global aquaculture raises concerns about its sustainability, especially with production expected to increase in the coming decades. If low-input systems are unable to scale up production, and commercial production in open systems is causing a variety of environmental problems, what is the way forward?

A Deep Dive into Next-Generation Aquaculture

“When we compare aquaculture technologies, two stand out in terms of sustainability potential: land-based recirculating systems and offshore aquaculture,” says Dane Klinger, visiting researcher at Princeton University and director of biology at the aquaculture company Forever Oceans. Moving aquaculture on land or offshore can reduce many of the key environmental problems with today’s commercial aquaculture systems, including habitat loss, freshwater consumption, and pollution.

Offshore aquaculture systems are marine net pens placed far from shore in the open ocean, where deeper water and stronger currents can better dilute the waste from the fish farm than in coastal systems.45 Farther offshore there are fewer nutrients and less biodiversity than in sensitive coastal ecosystems, so fish waste is quickly dispersed and absorbed into the marine food web.46

“We have this vast ocean that contributes less than 2% of the world’s food,” explains Jerry Schubel, president and CEO of the Aquarium of the Pacific. Today, marine aquaculture only takes place in the narrow strips along our coasts, where farming fish not only presents a risk to the surrounding ecosystem but also has to compete with other coastal economic activities.47 Moving into the open ocean allows fish farmers to avoid these problems.

Offshore aquaculture thus harnesses the benefits of marine aquaculture while minimizing the negative environmental impacts. Unlike land-based aquaculture, there is no need for pumping or heating water, and the pollution and habitat risks that are problematic in shallower, coastal waters are much reduced in deep offshore waters.

“Advantages of offshore aquaculture greatly outweigh any benefits of closed systems on land,” Schubel argues. There are already a few fish farms operating in the open ocean, including one growing sashimi-grade yellowtail in Hawaii and another growing shellfish on longlines off the California coast. Last year, Norway approved an offshore salmon farm built with advanced technology to enable remote operation. Someday, motorized sea cages may roam the oceans autonomously, fattening up fish with automated feeders until a boat comes to harvest the mature fish.

Of course, not all fish species can be cultured in ocean waters. For freshwater species, and to farm fish in locations far from the ocean, moving aquaculture production into land-based systems offers the most potential to reduce environmental impacts. In recirculating aquaculture systems (RAS), fish are farmed in indoor tanks, creating the right aquaculture environment using pumps, heaters, aerators, and filters.

These closed environment systems can provide tremendous environmental advantages. As implied by the name, recirculating systems treat and recycle water to reduce the amount actually consumed.48 RAS are designed to achieve nearly 100% water recycling, but a small amount of water is always lost to evaporation and incorporated into the fish biomass.49 Water recirculation has a huge advantage over flow-through systems in terms of freshwater demand, since flow-through systems require continuous new water withdrawals.

Another key advantage of closed, land-based aquaculture is that it can virtually eliminate pollution risks. RAS use settling basins and biofilters to remove fecal matter, excess feeds, and toxins from the water.50 Since waste products in RAS are collected instead of released to the environment, they can eliminate nitrogen and phosphorus emissions that can pollute waters in marine net pen and flow-through systems.51 Processing these effluents requires energy, and the waste does have to go somewhere: either a sewage treatment plant or landfill. However, the ability to fully control the flow of effluent provides a major advantage over open aquaculture systems, where there is free exchange of polluting nutrients between the fish farm and the environment.

Finally, land-based RAS open the door for aquaculture to occur virtually anywhere, including urban environments.52 Rather than being tied to coastal environments, land-based RAS can be sited on degraded or already-developed land, resulting in minimal habitat loss. Responsible siting is not a guarantee, however, and would rely on appropriate land-use planning.

Land-based systems open the door for aquaculture to occur virtually anywhere.

There are some commercial RAS facilities operating in developed countries today. In land-locked Iowa, for example, a family of former hog farmers have started farming barramundi using RAS technology. A Massachusetts start-up is proposing to use RAS to raise a genetically modified “AquAdvantage” salmon that grows faster and needs less feed than traditional farmed salmon.

Seafood Watch, the organization that provides sustainability ratings for seafood products, gives fish farmed in RAS high ratings. “Right now, Seafood Watch recommends all farmed fish from RAS as a ‘Best Choice,’ since these systems generally score well on many of our metrics like effluent and disease,” explains Tyler Isaac, an aquaculture scientist with Seafood Watch. Some farmed fish from open systems are rated “Avoid” due to their environmental impacts, although the ratings vary by location.53

The Role of Energy as a Substitute

While moving offshore or on-land can solve many of aquaculture’s environmental challenges, there is one resource use that goes up in these systems: energy use. In many cases, energy use is still coupled to greenhouse gas (GHG) emissions, which creates a sustainability trade-off for these next-generation aquaculture technologies.

The separation from the natural environment that characterizes closed, land-based systems drives higher energy demand. RAS rely on mechanization and industrial energy to provide functions like water exchange and filtration that, in an open system, are provided by ecosystem services.54 Pumps, filters, heaters, and aerators running on electricity or liquid fuels allow RAS to contain and collect fish waste, recycle water, and farm fish indoors. The totally self-contained environment that gives RAS its environmental advantages is entirely dependent on energy.

Most energy use for RAS is in the form of electricity,55 and since the electricity mix varies by region, so too will the greenhouse gas (GHG) emission impacts of high-energy RAS.56 A study of RAS in Canada found that global warming potential was 63 percent lower when modeled with the Canadian average electricity mix, which is mostly low-carbon hydropower, compared to the coal-fired electricity grid in Nova Scotia.57 Another study conducted in France found very little difference in GHG emissions between a raceway and RAS, even though the RAS had significantly higher energy use, because the electricity mix in France is very low-carbon.58

Regions that already have low-carbon electricity are well-placed to harness the benefits of RAS without major emissions consequences. Combining low-carbon energy with the low environmental impacts of RAS can offer a best-case scenario for aquaculture production. However, for producers, electricity cost is often the more pressing concern than emissions, so to have both economically and environmentally successful RAS deployment will depend on an energy supply that is both cheap and low-carbon.

Next-generation aquaculture underscores the importance and urgency of a future with cheap, low-carbon energy.

Marine aquaculture has much lower energy demand than RAS.59 However, moving fish farms into the open ocean will increase energy use compared to today’s typical marine aquaculture, which takes place near the coasts. Boats have to travel farther to manage the operation and harvest fish, burning diesel fuel all the while.60 Alternatively, farms can use automated equipment to run daily operations remotely, but this also requires energy.61 By removing fish farming from the crowded and ecologically sensitive coastline, open-ocean aquaculture also uses energy to reduce other environmental impacts.

The energy needs of open-ocean aquaculture are in some ways more comparable to wild-capture fishing, where energy use is measured in liters of diesel fuel per ton of fish harvested. However, offshore aquaculture promises a guaranteed catch at a known location; wild capture involves an uncertain harvest and often much longer boat trips. Nonetheless, maintenance of offshore fish farms will depend on energy from liquid fuels, tying it to GHG emissions, at least until today’s diesel-powered open-ocean vessels are electrified or a viable low-carbon liquid fuel is developed.

Automation may be able to reduce the number of management visits necessary with open-ocean aquaculture, but periodic site visits for harvesting and upkeep will still be needed. Mechanical feeders and monitoring technology also need an energy source, and distant offshore aquaculture sites can’t be easily connected to the electricity grid. In the near term, offshore fish farms will likely rely on stored liquid fuel,62 but there are conceptual proposals to develop systems that run on renewable energy sources like solar, wind, or wave power.63

In sum, the two aquaculture technologies with the greatest potential to minimize fish farming’s environmental impacts—offshore aquaculture and land-based RAS—both rely on greater energy inputs compared to today’s dominant systems.

The importance of energy in substituting for aquaculture’s impacts mirrors energy’s role as the “master resource” in other contexts. Indoor farming, for example, offers the ability to grow food without any arable land thanks to artificial lights, using electricity to create a year-round growing season. Desalination uses energy to open the door to plentiful freshwater from the oceans, relieving pressure on surface and groundwater sources that are habitat areas. Energy allows humans to substitute for ecosystem services, which can redound to environmental savings if it means meeting our material needs without clearing land for agriculture or damming rivers into reservoirs.

However, energy use remains largely coupled to greenhouse gas emissions in our fossil fuel-based energy system. Next-generation aquaculture systems offer the potential to greatly reduce the pollution, water use, and habitat impacts that characterize today’s commercial fish farms, but at the expense of greater climate impacts, at least for now. The role of energy use in next-generation aquaculture only underscores the importance of innovation into cheap, low-carbon, abundant energy sources.

Challenges for Moving Aquaculture On Land or Offshore

Today, global aquaculture production is still dominated by inland and coastal open systems. Next-generation fish farming practices like RAS and offshore aquaculture remain niche, since the higher costs and new risks associated with them have slowed deployment.64

While RAS producers have greater control over their operations in many ways, they are also vulnerable to different risks. In 2014, a power outage at a land-based salmon farm in Nova Scotia killed the entire stock of 12,000 fish.65 Capital costs are usually higher with RAS, and the rate of return is typically lower than conventional net pen systems.66 “Not a lot of RAS systems have reliably made money,” says Dane Klinger, “but it’s a relatively new technology and a new space.” RAS thus offer environmental benefits but come at a greater cost; government support and private R&D are being leveraged to bring down these costs and encourage deployment.67

Scale presents another challenge for intensive land-based systems. Most RAS today are operating at a small scale due to high infrastructure and operating costs.68 While a typical net pen salmon system would produce thousands of metric tons of salmon annually, a typical RAS operation today produces at best a few hundred metric tons.69 “Larger RAS systems are technically feasible, but still impractical in terms of cost and energy demand today,” says Nathan Ayer of Dalhousie University. Cheap, low-carbon energy would go a long way toward making RAS more attractive to fish farmers and more climate friendly.

Red tilapia farmed on a river in Thailand.

Advocates of offshore aquaculture also face some barriers to widespread adoption. Operating in federal or international waters raises new legal and regulatory challenges.70 Fish farms in the open ocean can also be more dangerous to manage since weather and ocean conditions can be more extreme than near shore. Stronger currents and higher surf also present a greater risk of damage to the aquaculture equipment.71 In bad weather, ships may not be able to reach the site at all.

Finally, there are some species that will be very difficult to raise in aquaculture of any sort. Bluefin tuna, for example, are a popular and highly valued delicacy in Japan and other sushi-loving countries, but their large size, temperamental disposition, and voracious appetite make them technically difficult to farm.72 “For high-trophic-level species like bluefin tuna, I think the natural world does a much better job of producing those species than we’ll ever do,” says Keegan McGrath, a fisheries biologist. Currently some bluefin tuna are “ranched,” where juveniles are caught in the wild and fattened up in net pens to reach marketable size.73 However, a research team in Japan has successfully grown bluefin tuna from eggs to maturity in an aquaculture environment, and while production is still at a small scale, they expect to produce 6,000 tuna a year by 2020.74

Solutions on the Horizon

“We need to look at aquaculture in terms of the global food supply,” argues Kim Thompson of the Aquarium of the Pacific. No food production is without environmental impacts, especially when it comes to animal products. Fish farming produces high-quality animal protein, generally with fewer environmental impacts than meat. People will eat plenty of meat in the coming decades as well, but fish can be one of the lowest-impact animal foods when it comes to the environment.

The aquaculture sector is poised to undergo a major transformation this century. Fish farming has already surpassed wild capture as our main source of seafood, and experts expect it will grow to meet nearly all new demand in the coming decades. To ensure a more sustainable future for fish farming, commercial aquaculture cannot continue to integrate intensive production with sensitive ecosystems along coasts, rivers, and lakes.

The future of sustainable aquaculture lies on land and offshore.

A return to low-input extensive systems is not a feasible option, however, given the volume of seafood demand and the need for export production. Instead, the future of sustainable aquaculture lies on land and offshore. Recirculating aquaculture in land-based tanks allows for total control of waste and minimal freshwater consumption. Offshore aquaculture takes advantage of open ocean waters to dilute pollution and removes fish farming from the sensitive and crowded coastal environment.

Both these next-generation aquaculture solutions rely on greater energy inputs to substitute for direct environmental impacts. This underscores the importance and urgency of a future with cheap, low-carbon energy, since otherwise the benefits of next-generation aquaculture will be countered with greater climate impacts. This trade-off of energy use, emissions, and environmental impacts must be carefully navigated at a regional and local level today. Nonetheless, the 21st century will see aquaculture rise to dominate the seafood sector, and energy will be the key to ensuring its sustainability.

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