The science of sustainable seafood, explained

The future of food from the sea, explained

In the year 2050, Earth will have almost 10 billion humans who will eat over 500 billion kilograms of meat. That is 2 billion more people and 177 billion more kilograms of meat than Earth currently has. With land-based meat fraught with climate and environmental impacts, how much animal protein can be sustainably supplied by the ocean? A new (open access) paper in Nature titled, The Future of Food from the Sea, answered that question and provided an economic roadmap for sustainable ocean food production.

The authors conclude that by 2050, the ocean could sustainably provide 80-103 billion kilograms of food, a 36-74% increase compared to the current yield of 59 billion kilograms. Crucially, the 2050 numbers were not a simple calculation of the carrying capacity of food production, but instead reflected the economic realities of growing and harvesting food in the ocean. The authors identified four key steps towards a more bountiful ocean:

  1. Improve fishery management
  2. Implement policy reforms to address mariculture
  3. Advance feed technologies for fed mariculture
  4. Shift consumer demand

In this post, I explain the numbers behind potential food production in the ocean and what the policy and governance process might look like going forward.

A mussel farm from below off the coast of Galicia, Spain.
A mussel farm off the coast of Galicia, Spain. Who knew mariculture could look so cool? Shutterstock | David Villegas Rios

Why get food from the sea instead of from land?

Increasing food production on land is difficult due to declining yield rates and general land and freshwater scarcity. Already, over half of all arable land and over 90% of freshwater is used in food production. Runoff from farms is a major source of water pollution and eutrophication.

Of all the food humans require, protein is the most impactful macronutrient to produce. Not only does it have a disproportionate carbon footprint, but livestock production is the largest driver of deforestation and biodiversity loss worldwide. Most increases in terrestrial food production come from replacing tropical forests with farms.

Increasing protein production from the sea should be part of the solution. It has a much lower carbon footprint and far fewer biodiversity impacts. Maximizing sustainable seafood will make achieving 2050 climate and biodiversity goals much easier.

Seafood is also healthier than livestock. It is leaner and contains several micronutrients that are difficult to obtain from land-based food.

Terrestrial aquaculture has some similar issues that other land-based meat production has, especially with freshwater. Though recirculating aquaculture farms are becoming more common, untreated aquaculture wastewater is highly pollutive. Though aquaculture colloquially refers to any farmed fish, in this paper (and blog post), “aquaculture” is specific to farmed species on land. Farmed species in the sea is called mariculture.

Fisheries

Now that I’ve established why food from the sea is a necessary and good idea, let’s get into the science behind the paper. Currently, wild fisheries account for 83.5% (49.3 billion kg) of protein from the sea, while bivalve mariculture and finfish mariculture are much smaller sources. By weight, 78.7% of monitored fisheries are currently sustainable. Overfishing reduces the long-term food supply by unsustainably depleting populations. Improving management so all are maximally sustainably fished would increase yields by 16% to 57.4 billion kg of food. Lead author Dr. Christopher Costello said, “We’ve had a history of overexploiting many fisheries, but we’re seeing governments starting to implement better fisheries management policies. And when you rebuild fisheries, you restore the health of the ocean and that allows you to have more food.”

But there are challenges to getting all fisheries sustainable. Though fishery science and management has improved significantly in the last few decades—the technology to sustainably manage fisheries exists—the worldwide capacity is missing. Countries with the financial and scientific means to manage their fisheries and enforce regulations have mostly healthy or recovering fish populations, countries without the capacity generally don’t. Increasing fishery yields will require developing countries to invest in their fishery management capacity.

Mariculture has much more potential to expand and will be where most of the food production gains come from.

Mariculture

While fisheries are hindered by capacity problems, mariculture is constrained by regulations that are either too lax, leading to environmental harm, or “overly restrictive, convoluted and poorly defined.” The variance in mariculture policy from too loose to too restrictive depends mostly on the type of mariculture, unfed or fed.

Unfed mariculture are animals that filter seawater for food, typically bivalves like mussels, clams, oysters, and scallops. Farmed bivalves are perhaps the lowest impact food on the planet. They have a low carbon footprint and require very few inputs—farmers simply place baby bivalves on ropes or in baskets and let them grow naturally. The authors estimate that bivalve mariculture could produce 80.5 billion kg of food based on current prices, though demand won’t be high enough to make it feasible. There are hardly any downsides to unfed mariculture, but regulations have mostly been restrictive rather than supportive—currently only 2.9 billion kg is produced each year.

An oyster farm underwater.
Oysters are a great example of unfed mariculture. Shutterstock | Divedog

Non-bivalve species like Atlantic salmon and farmed shrimp are considered fed mariculture as they require feed and/or other inputs. The environmental impact of those inputs is the largest component of the sustainability of fed mariculture. Currently, 75% of fed mariculture requires some kind of wild fish input (fish meal or fish oil). Since wild fish have ecological limits, fed mariculture does too… unless farms develop new ways to feed their species with less wild fish inputs. “More rapid alternative feed adoption and efficiency improvements in aquaculture will be key for scaling sustainable marine production,” said Dr. Halley Froehlich, one of the co-authors. From the paper:

Alternative feed ingredients—including terrestrial plant- or animal-based proteins, seafood processing waste, microbial ingredients, insects, algae and genetically modified plants—are rapidly being developed and are increasingly used in mariculture feeds.

The development of technology to replace fish meal and oil is the biggest variable in how much food can be produced from the ocean. Researchers ran scenarios reducing fishmeal and fish oil requirements by 50% or 95% from current levels—those technological breakthroughs would increase food supply by 17.2 billion kg and 174.5 billion kg respectively. Fed mariculture currently produces 6.8 billion kg of food per year.

Arial photo of a salmon mariculture farm off the coast of Hordaland, Norway
A salmon farm off the coast of Hordaland, Norway. Shutterstock | Marius Dobilas

The economics of food from the sea: supply and demand

Ecological conditions like water temperature and productivity determine suitability for mariculture, but researchers added an economic variable (i.e. capital costs of equipment, operating costs, etc.) to assess feasibility. Essentially, they determined if an area of the ocean was both ecologically viable based on environmental conditions, AND economically viable for mariculture depending on the sale price of the species and the cost of feed. Doing so, the researchers were able to construct global supply curves for each of the three types of ocean protein. Wild fisheries’ supply depends on management reform, fed mariculture supply depends mostly on technological innovation in feed, and unfed mariculture supply depends largely on policy reform.

Our supply curves suggest that all three sectors of ocean food production are capable of sustainably producing much more food than they do at present. The quantity of seafood demanded will also respond to price.

Figure 3 from Costello et al. 2020. A figure showing the supply curves for wild fisheries, finfish mariculture, and bivalve mariculture
Graphs show current production and average price in each sector: marine wild fisheries (a, left), finfish mariculture (b, middle) and bivalve mariculture (c, right). In wild fisheries (a), supply curves for annual steady-state edible production are shown under three different management scenarios: production in 2050 under current fishing effort assuming that fishing only occurs in fisheries that are profitable (F current); the economically rational supply curve aimed at maximizing profitability (rational reform); and a reform policy aimed at maximizing food production, regardless of the economic considerations (MSY). In finfish (fed) mariculture (middle), supply curves show: future steady-state production under current feed assumptions and policy reform (policy reform); sustainable production assuming policy reform and a 50% reduction in fishmeal and fish oil feed requirements (technological innovation); and sustainable production assuming policy reform and a 95% reduction in fishmeal and fish oil feed requirements (technological innovation (ambitious)). Bivalve mariculture shows current production and an increase simply based on policy reform. In all cases, feed ingredients are from the economically rational reform of wild fisheries. From Costello et al. 2020.

Once the supply curves were established, researchers added demand curves to see how price would interact with availability. At the intersection of those two curves is their estimate for future food from the sea. In the figure below (Fig. 4 from the paper) you can see price on the left, total production on the bottom, and the supply curves from above in black. Multiple demand scenarios across the three sectors are shown. The first (in green) shows if demand remains the same as today—this is unlikely as the population begins to grow. The second (purple) takes population and income growth into account but assumes consumer sentiment towards seafood remains the same. The third (red) shows a higher demand scenario where consumer sentiment towards seafood also rises.

Supply and demand curves for marine wild fisheries (a), finfish mariculture (b) and bivalve mariculture (c). In each panel, the solid black line is the supply curve from the above figure: for wild fisheries, the rational reform scenario is shown, and for finfish mariculture the technological innovation (ambitious) scenario is shown. Future demand refers to estimated demand in 2050; extreme demand represents a doubling of the estimated demand in 2050. The intersections of demand and sustainable supply curve (indicated with crosses) provide an estimate of the future food from the sea. Points represent current production and average price in each sector. From Costello et al. 2020

Under current demand, food from the sea would supply just 62 billion kg of food per year in 2050. A normal demand scenario estimates 80 billion kg while a higher demand scenario estimates 103 billion kg.

A figure showing Sources of Potential Food from the sea in 2050
Potential food from the sea in 2050 by sector under different demand scenarios. Data from Costello et al. 2020.

The path to sustainable food from the sea

Based on the ecological and economic limits of producing food in the ocean, the authors identified four steps to sustainably increase food from the sea:

1. Improve fishery management

Improving fishery management will maximize the amount of wild food available to humans and feed for aquaculture and mariculture. Regulations have improved dramatically over the past few decades, but there is still room for improvement. A major focus should be on developing countries that don’t have the capacity to manage and enforce regulations. 

2. Implement policy reforms to address mariculture

Why is the ocean not filled with farmed bivalves?? They are one of the lowest impact foods on the planet! Regulations need to encourage more bivalve and unfed mariculture.

On the other hand, some mariculture regulations in the fed sector need to be tightened to limit impacts. However, as with all food production, there will be environmental trade-offs (emphasis added):

Increased mariculture production will require management practices and policies that allow for environmentally sustainable expansion, while balancing the associated trade-offs to the greatest extent possible; this principle underpins the entire analysis. We find that substantial expansion is realistic, given the costs of production and the likely future increase in demand.

Photo of mariculture pens off the coast of Greence
Mariculture off the coast in Greece. Shutterstock | Dimitrina Lavchieva

3. Advance feed technologies for fed mariculture

Finfish mariculture (and aquaculture) has the greatest potential for expansion. Right now, it is limited by feed derived from wild fisheries. Improving feed technology is the biggest variable in future food production, but could also come with trade-offs.

Ambitious technical innovation (that is, the substitution of marine ingredients with terrestrial-sourced proteins) can help to decouple fed mariculture from wild fisheries, but will probably refocus some pressure on terrestrial ecosystems.

4. Shift consumer demand

The economics of increasing the oceanic food supply only makes sense if people want to eat it. Under a normal demand scenario, food from the sea will make up only 12% of the planet’s necessary animal protein increase (compared to 17% of current amounts). A higher demand scenario would make up 25% of the necessary increase. The more food from the ocean, the better, as it preserves more biodiversity and has a lower climate impact than the alternatives. However, there are several barriers to increasing consumer demand.

People in developed countries (who consume the most seafood) are less accustomed to cooking fish at home; seafood has the highest proportion consumed at restaurants of all meats. Shifting at home diets to include more seafood will require more recipes and instruction. Governments can step in here, too. For example, the U.K. funds Seafish, an organization meant to encourage U.K. citizens to consume local seafood.

Another consumer-perspective problem is that seafood has a poor sustainability reputation.

Widely publicized reports about climate change, overfishing, pollution and unsustainable mariculture give the impression that sustainably increasing the supply of food from the sea is impossible.

Though this was a warranted reputation in the 1980s, the sector has made tremendous strides since then. Most monitored fish populations are either healthy or recovering; 78.7% of fish (by weight) comes from a biologically sustainable population.

Environmental NGOs have an important role to play in this part of demand. Though they have mostly been critical of the seafood sector, promoting sustainable food production from the sea would benefit global biodiversity as food trade-offs on land are often more costly than trade-offs in the ocean. Instead of fighting fisheries and mariculture, more environmental NGOs should encourage their sustainable development.

Public perception of ocean conservation does not match the science. As the most public-facing institution, environmental NGOs should take the lead in changing perceptions and inspiring increases in demand.

Sustainably feeding 10 billion people is the climate and conservation issue of the 21st century. Society needs to end hunger and malnutrition while protecting as much wilderness and biodiversity as possible. The ocean can and should play a major role. Dr. Costello summed it up nicely:

“If done sustainably, you could actually increase food from the sea, and by an outsize proportion relative to expansion of land-based food, and it could be done in a way that's much more environmentally friendly for the climate, biodiversity and other ecosystem services than food production on land.”

Check out his short blog about the paper here.

Max Mossler

Max Mossler

Max studied environmental perception & policy in grad school. He thinks a lot about how other people think about the planet. He is the managing editor at Sustainable Fisheries UW.

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