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Food System Primer

Seafood

Background

Myanmar fish

Fisherman in Myanmar. The cone-shaped net in his boat traps fish.

Throughout history, people have relied on aquatic plants and animals for food, particularly among island and coastal communities. If aquatic species are not overharvested, these resources can be sustained for countless generations.

Photo public domain.

Click images for captions

The wealth of the sea belongs to the dead, the living, and those yet to be born.

– Asian proverb

This proverb, common to coastal fishing communities, speaks to the importance of learning from the past (the dead) and conserving ocean resources for future generations (those yet to be born).1

Throughout history, people have relied on aquatic plants and animals for nourishment, particularly among island and coastal communities. For Samoan islanders, sea animals like eels, worms, turtles, and sharks were a central part of traditional diets. Samoan fisherfolk were deeply attuned to their environment, and if they determined a particular species was threatened by overfishing, a village council would put a halt to those activities until it was safe to resume.2

Other cultures found ways to cultivate their own aquatic plants or animals for food—a practice called aquaculture. Ancient Egyptians, for example, built inland ponds and stocked them with fish and plants, while a system of elaborate canals supplied the ponds with fresh water.3

Today, aquatic animals are among the last major food sources still hunted from the wild. Once-plentiful fish populations, however, are threatened by a crisis of overfishing, hastened by industrial methods that operate on an unprecedented scale. With wild species in decline, more and more seafood is farmed, but is aquaculture necessarily a more sustainable alternative?

Wild-caught seafood

Seine

About 400 tons of mackerel caught in a purse seine (a type of net). Chile.

The vast majority of global seafood harvests use gigantic nets that are pulled through the water at varying depths or along the sea floor.4

Photo credit: C. Ortiz Rojas, NOAA Photo Library.

Bycatch

Separating shrimp from bycatch off the coast of North Carolina.

Industrial fishing methods can have devastating effects on aquatic life. Nets often scoop up large numbers of unwanted animals, including fish, seabirds, and aquatic mammals; these “extras” are called bycatch. Some of these animals are kept for sale, but many are thrown back to the sea, usually dead or dying. In the shrimp harvesting industry, only 5 percent of what some trawlers catch is actually shrimp, and the rest is bycatch.6

Photo credit: NOAA Photo Library.

Parrot fish

Parrotfish are the housekeepers of coral reefs—grazing on algae, removing dead coral, and clearing the way for new coral growth. In many reef ecosystems, overfishing has diminished populations of parrotfish, allowing algae to take over.10

The combined effects of overfishing, pollution, and climate change have transformed many of the ocean’s once-vibrant reefs into little more than rubble, seaweed, and slime.10,11 Efforts to halt fishing in coral reefs have shown promise in protecting these fragile ecosystems.12

Photo credit: Nick Hobgood. Creative Commons CC BY-SA 3.0.

Click images for captions

Many island and coastal communities still rely on traditional fishing tools like spears, rods, traps, and hand-thrown nets. Samoan islanders, for example, even developed a specialized rope noose for snaring sharks.2 The vast majority of global seafood harvests, however, employs gigantic nets that are pulled through the water at varying depths.4

Industrial fishing methods can have devastating effects on aquatic life. Nets often scoop up large numbers of unwanted aquatic animals, called bycatch. Some of these animals are kept for sale, but most are thrown back to the sea, usually dead or dying. Bottom trawling (dragging a net across the sea floor) and dredging (using a large metal basket to scoop up shellfish like scallops, clams, and oysters) are the most damaging in this regard.5 In the shrimp harvesting industry, for example, only 5 percent of what some trawlers catch is actually shrimp, and the rest is bycatch.6 Dragging nets and dredges across the sea floor also destroys fragile sea sponges, corals, and other critical members of ocean ecosystems.5

For many aquatic species, centuries of overfishing—both with traditional and industrial methods—have depleted populations well below historic levels.7 Some species, such as Atlantic salmon, have been nearly eliminated from many of their natural habitats,8 affecting people who depend on those animals for food and livelihoods.

Overfishing is not just the result of harvesting animals for people to eat. In 2010, close to 20 percent of wild-caught seafood was ground into fishmeal and fish oil and fed to farmed animals, including farm-raised fish such as salmon, as well as pigs and chickens.7 Harvesting small wild fish to feed farmed fish can contribute to problems of overfishing, and can deprive wild carnivorous fish of their food sources.9

Aquaculture: farming seafood

Global Fisherie

Aquaculture is the fastest growing industry in food production, and now supplies roughly half of all seafood eaten by people.7 In 2011, for the first time in modern history, global aquaculture production surpassed global beef production.16 Most seafood is still caught from the wild, but not all wild-caught seafood is for people—close to 20 percent is ground into fishmeal and fish oil and used as animal feed.7

Image credit: Epipelagic. Creative Commons CC BY-SA 3.0.  Adapted from the U.N. FAO.

Aquaculture map

Aquaculture production, by country, in metric tons per year.

Most farm-raised seafood comes from Asia. In 2010, China produced over 60 percent of the world’s farm-raised seafood. China is also the world’s leading consumer and exporter of seafood.7 The U.S. is the second largest seafood consumer in the world, but most of that seafood comes from overseas. In 2011, the U.S. imported 91 percent of its seafood from other countries.17

Image credit: Michael Milli, Johns Hopkins Center for a Livable Future.

Shrimp farm

Shrimp farms in Vietnam.

Mangroves are a type of coastal forest in tropical and subtropical areas. They provide an abundance of services, including barriers against tropical storms, habitats for juvenile fish, and plants that people use for food, fuel, and shelter.18 An estimated 20 percent of the world’s mangroves have been destroyed in just 25 years.18 Deforestation to farm shrimp—the most popular seafood in the U.S.19—has been responsible for close to 40 percent of these losses.20

Photo credit: American Museum of Natural History, 2009. Creative Commons CC BY-NC-SA 2.0.

Oyster farm

On this Australian oyster farm, oysters are raised in submerged bags attached to the poles.

Aquaculture is not just for raising fish. Farmers grow shellfish such as clams, oysters, and mussels by suspending them in water by ropes, trays, or mesh bags. Farming these animals can improve water quality—they are called “filter feeders” because they strain algae and other suspended particles out of the water for food.

Photo credit: Saoysters. Creative Commons CC BY 3.0.

Aquaponics

Students taking water samples at the CLF Aquaponics Project.

Aquaponics is a type of recirculating aquaculture that produces both fish and plants. The plants are grown in floating beds, while the fish swim either below the plants or in separate tanks connected by pipes. Instead of creating a pollution problem, the waste from the fish fertilizes the plants, while the plants help clean the water.

Photo credit: Larry Canner.

Click images for captions

Aquaculture (farming seafood) is the fastest growing industry in food animal production. Almost half  the seafood consumed worldwide is now farm-raised.7

There are many different kinds of aquaculture systems. Some are built inland or along the coast, while others raise animals in the sea. For example:

  • Raising animals in ponds is the oldest form of aquaculture. This method is popular in the U.S. for raising catfish. 
  • Raceways are artificial channels (like lanes of a swimming pool) with a flowing current, which flushes out fish waste.
  • Recirculating systems raise fish in filtered tanks. The water is continually cleaned and recycled—just like in an aquarium.
  • Marine aquaculture uses cages anchored to the sea floor, or floating nets. This system is often used for salmon.

In some cases, particularly for shellfish (see caption), aquaculture can be a more sustainable alternative to harvesting animals from the wild.

Aquaculture can also contribute to environmental and public health problems. Like industrial hog, poultry, and cattle facilities, aquaculture farms often confine large numbers of fish in a relatively small area—many offshore salmon farms, for example, stock over 300,000 fish at a time.13 The large quantities of waste from these farms can pollute surrounding waters, harming ocean wildlife.9 In such crowded conditions, diseases can spread among fish and into the wild.14 Antibiotics given to fish to compensate for unsanitary conditions can pose human health risks if the drugs remain in the edible parts of fish, or if their use contributes to antibiotic resistance.15 Farmed fish, such as Atlantic salmon, often escape into the wild. Atlantic salmon are larger and more aggressive than their wild cousins, and can outcompete native species, disrupting aquatic food chains.14 Farm-raising fish can also contribute to problems of overfishing.

Seafood in diets

Power plant

Emissions from a coal-fired power plant.

Much of the pollution from industrial activity winds up in our streams, rivers, and oceans, where it can accumulate in the tissues of aquatic plants and animals. Globally27 and in the U.S.,28 coal-burning power plants are the largest human-caused source of airborne mercury emissions.

Photo credit: Emilian Vicol. Public domain.

Click images for captions

Between 1983 and 2003, total U.S. seafood consumption more than doubled. By 2009, the U.S. was second only to China as the largest seafood consumer in the world.21 On a per capita basis, the typical American eats 30 percent more seafood than the global average,21 yet 2010 U.S. Dietary Guidelines advised Americans to eat even more.22 Is this good advice?

Most fish and shellfish are good sources of nutrients, including vitamins, minerals, protein, and the omega-3 fats EPA and DHA. These fats are crucial for brain and eye development, and studies suggest they may have cardiovascular health benefits.23 Diets with a moderate amount of fatty fish, nuts, and olive oil (the so-called Mediterranean diet) have been shown to protect cardiovascular health, possibly because of the types of fats in these foods.24

There are also potential health risks associated with eating contaminated seafood. Much of the pollution from industrial activity—such as mercury from coal-fired power plants—winds up in our streams, rivers, and oceans, where it can accumulate in the tissues of aquatic plants and animals. Some toxic chemicals, such as the pesticide DDT, are still showing up in seafood long after the pesticides were banned.25 Because concentrations of certain contaminants tend to increase at each level of the food chain, larger carnivorous fish like sharks and swordfish generally pose the greatest risks for seafood consumers.26 Contaminants can also accumulate in the tissues of farm-raised fish that are given feed made with contaminated wild fish.26 See also Food Safety. 

Taken together, there are many important health, ecological, and economic considerations when making choices about seafood. For example, consumers may wish to limit their seafood consumption to sustainably-raised or sustainably-harvested species that are lower on the food chain.

Resources

The following list of suggested resources is intended as a starting point for further exploration, and is not in any way comprehensive. Some materials may not reflect the views of the Johns Hopkins Center for a Livable Future.

For teachers

Reports and websites

Videos

Academic journal articles

References

1. Kurien J. Traditional Ecological Knowledge and Ecosystem Sustainability: New Meaning to Asian Coastal Proverbs. Ecol Appl. 2014;8(1):S2-S5.
2. Armstrong K, Herdrich D, Levine A. Historic Fishing Methods in American Samoa. NOAA; 2011.
3. Costa-Pierce BA. Aquaculture in ancient Hawaii. Bioscience. 1987;37(5):320-331.
4. Watson R, Revenga C, Kura Y. Fishing gear associated with global marine catches I. Database development. Fish Res. 2006;79(1-2):97-102.
5. Watson R, Revenga C, Kura Y. Fishing gear associated with global marine catches II. Trends in trawling and dredging. Fish Res. 2006;79(1-2):103-111.
6. Davies RWD, Cripps SJ, Nickson  a., Porter G. Defining and estimating global marine fisheries bycatch. Mar Policy. 2009;33(4):661-672.
7. U.N. Food & Agriculture Organization. The State of World Fisheries and Aquaculture. Rome; 2012.
8. Parrish DL, Behnke RJ, Gephard SR, McCormick SD, Reeves GH. Why aren’t there more Atlantic salmon (Salmo salar)? Can J Fish Aquat Sci. 1998;55(S1):281-287.
9. Naylor RL, Goldburg RJ, Primavera JH, et al. Effect of aquaculture on world fish supplies. Nature. 2000;405:1017-1024.
10. Bellwood DR, Hoey AS, Hughes TP. Human activity selectively impacts the ecosystem roles of parrotfishes on coral reefs. Proc Biol Sci. 2012;279(1733):1621-9.
11. Pandolfi JM, Jackson JBC, Baron N, et al. Are U.S. coral reefs on the slippery slope to slime? Science (80- ). 2005;307(5716):1725-1726.
12. Mumby PJ, Dahlgren CP, Harborne AR, et al. Fishing, trophic cascades, and the process of grazing on coral reefs. Science. 2006;311(5757):98-101.
13. Milewski I. Bay Management and New Brunswick’s Salmon Aquaculture Industry. 2014.
14. Naylor R, Hindar K, Fleming IA, et al. Fugitive salmon: Assessing the risks of escaped fish from net-pen aquaculture. Bioscience. 2005;55(5):427.
15. Cabello FC. Heavy use of prophylactic antibiotics in aquaculture: a growing problem for human and animal health and for the environment. Environ Microbiol. 2006;8(7):1137-1144.
16. Larsen J, Roney JM. Farmed Fish Production Overtakes Beef. Earth Policy Inst. 2013.
17. NOAA. NOAA Fisheries Posts Statistical Report Card for U.S. Fisheries in 2011. NOAA Fish. 2012.
18. Food and Agriculture Organization of the United Nations. The World’s Mangroves 1980-2005. Rome; 2007.
19. National Fisheries Institute. Seafood’s Top 10 Most Popular Illustrate America’s Comfort Zone. 2014.
20. Polidoro BA, Carpenter KE, Collins L, et al. The loss of species: Mangrove extinction risk and geographic areas of global concern. PLoS One. 2010;5(4).
21. U.N. Food & Agriculture Organization. FAOSTAT. 2013.
22. U.S. Department of Health and Human Services, U.S. Department of Agriculture. Dietary Guidelines for Americans, 2010.; 2011.
23. Ruxton CHS, Reed SC, Simpson MJ a, Millington KJ. The health benefits of omega-3 polyunsaturated fatty acids: a review of the evidence. J Hum Nutr Diet. 2004;17(5):449-59.
24. Estruch R, Ros E, Salas-Salvadó J, et al. Primary prevention of cardiovascular disease with a Mediterranean diet. N Engl J Med. 2013;368(14):1279-90.
25. Dougherty C. Dietary Exposures to Food Contaminants across the United States. Environ Res. 2000;84(2):170-185.
26. Gormaz J, Fry J, Erazo M, Love D. Public Health Perspectives on Aquaculture. Curr Environ Heal Reports. 2014:1-12.
27. UNEP Chemicals Branch. The Global Atmospheric Mercury Assessment: Sources, Emissions and Transport. Geneva, Switzerland; 2008.
28. U.S. Environmental Protection Agency. Mercury: Basic Information. 2013.