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Inside the Mariculture Sub-Goal

Recently I went into a small food market and ---to my surprise---more than half of the products in the fresh seafood display were listed as farm-raised, including mussels, white gulf shrimp, tilapia, salmon grown in the U.S. and Ireland, organically-grown salmon and arctic char. 

Wherever we live, many of us have eaten farm-raised seafood even if we’ve never heard of aquaculture or mariculture.  Whether purchasing seafood from a market for cooking at home, or eating at a restaurant, sushi bar or oyster bar, if you selected tilapia, catfish, salmon, trout, ‘bronzini’, ‘barramundi, eel, sturgeon, sea bass or shellfish such as shrimp, oysters, mussels, clams and even some scallops or abalone, your food was probably raised by people. 

Why We Have a Mariculture Sub-Goal

If we had begun the Ocean Health Index project 30 years ago, farm-raised seafood might not have seemed important enough to include within the Food Production goal, because farm-raised species accounted for only a few percent of global seafood.  But during those thirty years our population grew from 4.5 billion to more than 7 billion, and feeding us all is now (in every sense) a growing problem. 

About one-quarter of us now rely on seafood for protein, essential fatty acids, vitamins and other nutritional needs. The problem is that wild populations can’t produce any more food than they already do.  Despite increased fishing effort, food from capture fisheries--- nearly 90% of it from the ocean---has stayed at about 90 million tonnes (also known as metric tons, or mmt) for a quarter-century.  Ocean seafood production is maxed out, but we need more food because 200,000 new people join our population every day---70 million every year---and they all have to eat.  The only answer is to find new and improved methods for growing food both on land and in the ocean.

If the oceans can’t produce more by natural processes, the only way to get additional seafood is to farm it---just like we do on land.  Since aquaculture will be so critical to our future and because it already provides 43% of total global fish and shellfish, including farm-raised seafood as part of the Food Production goal was now an easy decision. 
A Different View of the World

The map below cleverly shows the global distribution of aquaculture by adjusting land areas proportionally to the amount of farm-raised food they produce (1).  You can see that more than 90% of global aquaculture takes place in Asia and that China alone produces more than 60% of global aquaculture production.  

The Difference between “Aquaculture” and “Mariculture”

‘Aquaculture’ generally refers to all fish and shellfish production---freshwater and marine, though some studies use it only to mean ‘fish and shellfish raised in fresh water.’ In any case, most aquaculture production comes from freshwater pond and lakes, where people have raised fish for thousands of years. The remaining portion-- called ‘mariculture’-- comes from coastal marine farms in salt or brackish water where fish or shellfish are raised in floating cages, net enclosures, natural or artificial ponds, or closed circulation water systems. Owing to its focus on marine environments, the Ocean Health Index does not evaluate all aquaculture, but only that portion of seafood raised by mariculture. 

The long head start and relative simplicity of freshwater aquaculture help explain why it accounts for two-thirds of global farm-raised production. Since the 1970s improved techniques for farming marine fish, shrimp, mussels, clams and oysters, among others, have slowly raised mariculture production and it now contributes about one-third of farm-raised production. 

Mussel-growing field

If you have followed the news during recent years you’ll know that mariculture isn’t entirely benign. You’ll have seen reports about conflicts between salmon farmers and commercial or sport fishermen; oyster growers and proponents of wilderness areas; shrimp farmers and mangrove forest conservationists; or fish growers and seals that raid pens.  You may also have read that some Asian shrimp farms add antibiotics to mariculture feed---including some that are banned in the U.S.  --- which can promote the growth of antibiotic-resistant bacteria that can cause human infections. The U.S. and European Union ban the use of antibiotics for growth promotion and restrict their use to therapeutic purposes.

Everyone will gain when mariculture supports human wellbeing without polluting water, harming habitats or introducing alien species or genotypes to ocean ecosystems.

That’s why we structured the mariculture sub-goal so the score indicates how close a region’s current yield is to its maximum possible sustainable yield. A perfect score means that a country is sustainably harvesting the greatest amount of farmed seafood possible based on its own potential.

The Ocean is Tapped Out

Data from FAO (2) show the growing importance of seafood production by aquaculture as well as the ocean’s inability to produce more fish by natural processes than it already does. 

In 2011, the total world production of fish and shellfish was 154 mmt, 85% of which was eaten directly by humans.  Marine capture fisheries accounted for 51% (78.9 mmt); freshwater fisheries 7% (11.5 mmt); freshwater aquaculture 28% (44.3 mmt); and mariculture 13% (19.3 mmt). Between 2006-2011, while capture fisheries production stayed about the same, total aquaculture production increased about 2.6% per year, with freshwater production increasing slightly more than twice as fast (2.6% per year) as mariculture production (1.2% per year) (2).  

What Lies Ahead

What would be needed for mariculture to increase in the future? One factor would be new technology for developing offshore farms in deeper water. Even more important would be the development of new aquaculture feeds that don’t include the small, wild-caught pelagic marine fish species such as anchovies, herring, menhaden, capelin, anchovy, pilchard, sardines, and mackerel, that currently make up about 37% of the total marine capture fisheries landings, nearly all of which is processed into feed for aquaculture or farm animals (3).  We can’t harvest more of those fish for aquaculture without decreasing the food available for larger species targeted by fisheries as well as the food needed by marine wildlife such as whales, seals and seabirds. So development of plant-based substitutes for fish, fishmeal and fish oil in mariculture feed will be essential to improving the sustainability of current aquaculture as well as increasing future production.      

One other advance might also be important. Growing several species together (Integrated Multi-trophic Aquaculture, IMTA) could reduce some negative impacts and increase mariculture efficiency and resilience. In IMTA, wastes (uneaten food, excretions) from one species become inputs (fertilizers, food and energy) for growing others. For example, wastes from species that need feeding, such as finfish or shrimps, can nourish algae that serve as food for shellfish or herbivorous fish. Alternatively, the wastes can nourish seaweeds that can be harvested directly and marketed as wrappers for sushi, ingredients for soup, seasoning flakes other uses.  

Positive and Negative Impacts of Mariculture

To evaluate mariculture’s sustainability, we had to identify and weigh its effects.  Its positive impacts include food provision as well as jobs, wages and revenue to coastal economies (evaluated in the Livelihoods & Economies goal).  It may also draw tourists to some destinations, for example salmon farms in Ireland, though in other areas mariculture operations may compete for space with tourism activities such as bathing or sailing.  Negative impacts can include pollution of water by wastes, chemicals and pesticides used in culture; spread of diseases or alien species imported with seed or brood stock; introduction of alien genotypes through escape of cultured stock and subsequent interbreeding with native stocks; and destruction of habitat (e.g. destruction of mangrove forests to build ponds for shrimp aquaculture or smothering of the seafloor by settling of wastes or uneaten food).  We also gathered data that indicated whether nations were taking actions to reduce negative impacts (resilience). 

How we calculated the Mariculture sub-goal

As for all goals and sub-goals in the Ocean Health Index, Mariculture was evaluated in four dimensions:  Status, Trend, Pressures and Resilience. 

The goal is for each country to produce as much farmed seafood per unit area of coast as does the top-producing country--currently China--and to do it sustainably.  We had no theoretical way to estimate the maximum sustainable mariculture production possible for any country, so we used area-weighted production in the top-producing country as a reference value and we assumed that this value approximates what can be achieved anywhere given current ecological and technological conditions.

So the goal for each country is to have the same amount of production per unit area within the portion of its coastline that can support mariculture as does China. 

The status is calculated as the proportion of current sustainably-harvested yield to maximum possible sustainably-harvested yield within each country, based on each country’s own potential (estimated by the area of the strip of water 3 nautical miles wide running along the length of its entire coastline) and assuming that all of that area is equally useable for mariculture   This method doesn’t penalize countries that have less geographic area available for mariculture, though places with fewer sheltered bays or lower primary production could be at a disadvantage.   Species that have never been cultured in a country are not included in calculation of its score.

Fish farming and clam farming in Halong bay, Vietnam

Gauging mariculture sustainability is not easy and we relied on information from a Mariculture Sustainability Index (MSI) prepared by Trujillo (4).  For each country, we determined the yield of each species raised and multiplied it by a sustainability score for that species, based on Trujillo’s (2008) information about wastewater treatment, origin of feed (i.e. fishmeal or other) and the origin of seed (i.e. hatchery or wild caught). We then divided the sum of those values by the area available to mariculture in that country.      

To assess the likely near-term (5 year) future for mariculture globally and in each coastal country, we looked at the slope of the historical (5-year) production trends, assessed the intensity and importance of pressures that influence production (chemical pollution, nutrient pollution and pollution from ships and ports; and social pressures); and estimated how well nations were taking resilience actions to reduce those pressures through good governance and adherence to selected international agreements on biodiversity, water quality and mariculture.  Scores were only computed for the 85 reporting areas that could be assessed in all four dimensions.

How the countries scored:

The 10 countries with highest scores for Mariculture were:

     China: 100

     South Korea:  63

     Thailand:  62

     Taiwan (Province of China):  54

     Spain:  47

     Netherlands:  46

     France:  46

     Vietnam:  44

     Singapore:  43

     Japan:  40

High scores for the Asian countries were no surprise, as they dominate mariculture production. Spain, Netherlands and France scored relatively well owing to strong production of shellfish, in addition to some production of fish, primarily freshwater species, but also marine species such as seabass and seabream in France.  France is the largest European producer of farm-raised shellfish, mainly oysters, but also substantial quantities of mussels; and Spain is the second largest global producer (behind China) of farm-raised mussels, which account for nearly 90% of its marine production.  Mussels also dominate production in the Netherlands. France raises shrimp and several marine fish in one of its overseas territories, New Caledonia.  Detailed profiles of the history and current status of aquaculture and mariculture in these and other countries are available at http://www.fao.org/fishery/naso/search/en.


(1) Hall, S.J., A. Delaporte, M. J. Phillips, M. Beveridge and M. O’Keefe. 2011. Blue Frontiers: Managing the Environmental Costs of Aquaculture. The WorldFish Center. Penang, Malaysia.

(2)  FAO 2012. The State of the World’s Fisheries and Aquaculture. United Nations Food and Agriculture Department, Rome.

(3) Alder, J. and D. Pauly (eds.). 2008. A comparative assessment of biodiversity, fisheries and aquaculture in 53 countries’ Exclusive Economic Zones.’ Fisheries Centre Research Reports. Fisheries Centre, University of British Columbia.

(4) Trujillo, P., 2008. Using a mariculture sustainability index to rank countries’ performance. Pp. 28-56 In: Alder, J. and D. Pauly (eds.). 2008. A comparative assessment of biodiversity, fisheries and aquaculture in 53 countries’ Exclusive Economic Zones.’ Fisheries Centre Research Reports. Fisheries Centre, University of British Columbia.

(5) FAO 2010. The state of world fisheries and aquaculture 2010, Food and Agriculture Organization of the United Nations. Rome, Italy.   

(6)  Serrano, P.H. 2005. Responsible use of antibiotics in aquaculture. FAO Fisheries Technical Paper 469. Rome, 2005. Available online: ftp://ftp.fao.org/docrep/fao/009/a0282e/a0282e00.pdfAccessed January 24, 2013

(7)  Soto, D. (ed.). Integrated mariculture: a global review. FAO Fisheries and Aquaculture Technical Paper. No. 529. Rome, FAO. 2009.183p.