Expansion of sourcing of marine foods

One measure of the expansion of our use of the world’s oceans as our larder is the distance fishing fleets travel to meet our demands year upon year. Any such measure is strictly a minimum average value as seafood is a highly global commodity7, which can be caught in one location, processed at another and consumed in yet more distant places. Regardless of where it is caught, there is anecdotal evidence of seafood being processed where labour is the cheapest or where it can be rebadged to overcome import tariffs12.

Any measure of distance that seafood travels to consumers must also accommodate the rapid rise of mariculture in the proportion of seafood consumed. Here we show (Fig. 1a) that the minimum mean distance travelled to source the seafood we consume has increased continually from the 1950s (when global catch records started13) to the present. At least some of this migration of fishing activities was also caused by increased controls of fisheries in declared exclusive economic zones (EEZs), first as a result of the United Nations Convention on the Law of the Sea in the 1970s, and subsequently through consistent establishment of management systems (with diverse success) all over the national fishing areas. Nevertheless the need to source seafood from increasingly longer distances is clear.

Figure 1: Historical and projected use of global oceans. (a) The median minimum distance 1950–2011 that seafood is sourced from where it is consumed (bootstrap methods supply 95% confidence limits indicated by blue shading) combines wild capture and mariculture using the mapped position of origin directly to the nearest port where consumed. (b) The area of ocean used to supply seafood for 1950–2011 using the % of annual primary productivity required (PPR) of the available primary productivity (PP) for three exploitation levels (>10% (green), >20% (yellow) and >30% (red)) assuming fixed trophic transfer efficiencies for the associated mapped landings. (c) Percentage of ocean PPR to PP used from currently accessible ocean areas (depth <1,000 m) assuming fixed trophic transfer efficiencies for the associated mapped landings for 1950–2011. Monte Carlo methods provided the 95% confidence shading in blue. (d) Global consumption of seafood 1950–2011 and projected to 2100 based on the UN’s high, low and median levels of population estimates. Solid diamonds are FAO/UN’s future consumption estimates. Horizontal lines represent the estimated limits to global seafood production (wild and farmed combined) assuming limits to the fishmeal (marine-sourced) input to mariculture feeds restricted to 10% (lowest line), 7 and 5%, respectively (highest line). Full size image

Not all seafood taken is consumed locally. Most seafood now, whether wild or farmed, as we have shown, is sourced at great distances from where it is consumed. Country consumption levels for the early 1960s are shown in Fig. 2b. These are the consumers of the significant ocean production removed by fishing in areas mapped in Fig. 2a. Consumption was generally highest in countries that have long traditions of fishing and fish in the diet such as Norway, Iceland and Portugal. Most of these countries have large fleets that fish in the waters of other countries. Some countries do not have large fishing fleets but use imported seafood as a major protein source. By the 2000s (Fig. 2d) seafood consumption levels had generally risen and had greatly increased in Asia and Europe, which required their fleets to travel widely to maintain annual landings. Driven by demands for seafood, European fleets were fishing in the waters of countries of northwest Africa10 (see Fig. 2c), and China had deployed considerable distant-water fleets fishing throughout the Pacific and along the African coast14. The intensity and global nature of the seafood trade had greatly increased over this 50-year period15.

Figure 2: Where global seafood was historically produced and consumed. (a) Production in 1950s: the % of primary productivity required (PPR) of average primary productivity (PP) available to support seafood catches within country’s exclusive economic zone (EEZ). (b) National consumption estimated for circa 1961 in kg per capita. (c) Production in 2000s: the % of primary productivity required (PPR) of average primary productivity (PP) available to support seafood catches within country’s EEZ claims. (d) National consumption for 2009 in kg per capita. Full size image

Some countries, including many developing ones, rely on production from freshwater. Food and Agriculture Organization (FAO) reported that from 2001 to 2011 there were 352M t reported for marine areas compared with 6M t for freshwater7. Since 1950 to 2011 capture landings from marine sources have risen fivefold but for freshwater it was 45-fold. They reported 30M t (32% of global total) produced from marine habitats (which we will refer to as mariculture) in 2010 as against 62M t for freshwater (62%) with the balance in brackish waters. Freshwater production, however, can be dependent on marine-based feeds.

Increased use of ocean primary productivity

At the same time as we have sourced seafood from greater distances, we have utilized, through our harvested seafood and the mariculture it supports, an increasing proportion of calculated total annual ocean production. There is uncertainty associated with the calculation of ocean primary production using satellite ocean colour data such as that from SeaWIFS data used here, particularly in the most productive inshore and shelf areas where most seafood is taken. The area of ocean fished has increased (Fig. 1b), however, including those areas fished to an intensity that requires 30% or more of calculated in situ annual primary productivity to support it. A consideration of ocean areas that are accessible by most methods of fishing (those less than 1,000 m in depth) shows that we could be now using an average of nearly 40% of calculated ocean primary production in those areas (Fig. 1c). If, however, SeaWIFS data are underestimating primary production then this will be the worst-case scenario.

Most of the productive areas of the world’s seas are near the coast, and it is here that 80% of the wild-caught seafood is taken. The intensity of use within the marine EEZs claimed by maritime countries for fishing varies, but globally this has increased greatly. In the 1950s (Fig. 2a) most tropical and southern hemisphere waters yielded annual landings that were supported by only a small proportion of local marine primary productivity. By the 2000s, fishing was taking a much larger proportion of available production (Fig. 2c) and had greatly intensified throughout Asia and South America. In all but a few countries, fishing extracted 5% or more of ocean production from their waters.

Taken together with the logistics of fishing, these natural limits to ocean productivity6 restrict the harvest of wild seafoods. Despite an increasing demand for valuable seafood the expansionary trends in the sourcing of wild seafoods shown are markedly slowing.

Ability to meet future seafood demands

Global consumption of seafood has increased since the 1950s and, notwithstanding nature’s limitations, is projected to continue (Fig. 1d). Here we show projections to 2100 from historical data based on UN population projections, which vary by assumed human fecundity16. Expert UN future estimates expect considerable increase in consumption rates17 (diamond-symbols Fig. 1d). Given the trend from the last decade of wild-caught seafood landings it is expected that catches will remain largely static2; therefore, expected increases in consumption are widely anticipated to come through significant expansion in mariculture. Feeding most farmed fish, including farming freshwater fish which is 60% of all fish production7, currently requires wild-caught marine landings. In addition, feeds produced from marine fodder fish are used for terrestrial livestock production18.

We estimate the limits to global human consumption possible if wild-caught seafood landings remains relatively static but mariculture is expanded as anticipated. Carnivorous fish species cannot use carbohydrates as an energy source, and their required feeds are very rich in proteins and oils, traditionally provided by fishmeal and fish oils, rich in essential fats. As nutritional knowledge increases for mariculture species the inclusion of fishmeal and oil can be reduced; this is reflected by our scenarios using 5, 7 and 10% fishmeal inclusion. The limit to future global seafood consumption of 144 million tonnes (lower horizontal line Fig. 1d) is our estimate if overall feeds used contain only 10% fishmeal originating from wild sources. The bulk of the feed would initially be sourced from terrestrial agriculture including a wide variety of plant and rendered animal sources19,20. If, however, the content of wild-sourced fishmeal in mariculture feeds is reduced to only 7% overall, then a large increase to 177M t annually is achievable (middle horizontal line Fig. 1d). With the dependence on wild fish stocks further reduced, whether transforming further agricultural production or through new technologies, these limits could be lifted allowing the projected increase in global consumption to continue. Global production (wild and mariculture combined) to 220M t could be achieved if the overall fishmeal content was dropped to 5% (top horizontal line Fig. 1d). This will, however, require significant change because, in fact, the trend has been to have an even greater reliance on natural ecosystems for feeds and not the reverse. A full two-thirds of mariculture production requires formulated feeds now which is a substantial increase from 1980 when it was only 50% (ref. 7). In the meanwhile global seafood requirements can only be met if the viability of wild stocks and their supporting ecosystem are not compromised. The health of our marine ecosystems and the stocks they support remains vital.

We anticipate also that climate change will alter both production and consumption patterns of seafood by changing the productivity of marine areas1,21,22, the use of coastal land and in other ways as yet unexpected. In one projection, anticipated climate change will increase wild productivity by 2050 by providing a 6% increase in larger species directly consumed as seafood, and nearly 4% more of smaller species currently used as fodder1. If somehow through incentives, we could also consume the estimated 7M t annually currently discarded at sea23, then a total of 200M t of seafood would be available. If this increased production was realized then the extra fodder fish captured, but not used for mariculture, could be used for human consumption or provide increased inputs to livestock production on land18. At 200M t, the anticipated consumption corresponding to the mean projection of global populations would be met until about 20501, but after this time increases must come by further decoupling mariculture production from the limitations of natural marine ecosystems. Future feeds must not come from sources currently used to feed humans but from additional, currently untapped sources such as microbial or planktonic production. How then can we meet our future demands for seafood? Mariculture, and more broadly aquaculture, has potential to increase production through a variety of mechanisms; fish are effective at converting feeds to protein8 and improvements in nutrition will further improve this especially when combined with domestication and selective breeding. The availability of different protein and oil sources is increasing as key ingredients are refined, into protein concentrates for example, and new ones introduced, such as from insects and algae. Many mariculture species have been farmed for only a few generations and there is still much potential for selective breeding. For example, some individual carnivorous trout are better at using plant proteins while other individuals may be better at retaining valuable omega-3 fatty acids20. Atypical marine species, such as Senegalese sole that synthesize long-chain omega-3 fatty acids, may have valuable characteristics and be preferred.

Societal choice will influence future directions; genetically modified (GM) salmon that grow much faster were developed over 15 years ago and GM plants that produce high levels of long-chain omega-3 oils will be available in the next few years19. Our future may see salmon mariculture come onshore in recirculation systems and even stay in freshwater to reduce stress and disease while increasing growth efficiency. Integrated multi-trophic level marine systems that recycle wastes from farmed fish through harvestable crops such as seaweed, grazing abalone and filter feeding bivalves will expand.

In addition to our vital wild captures and harvest, seafood of the future is likely to be produced in a variety of ways. For basic food requirements there will be more production of marine plants (GM or otherwise). These could be in shallow coastal areas but they could be inland or even in suspension in huge volumes of seawater. In addition, proteins will be produced by growing a range of animals on massive scales without regard to omega-3 oil content or similar current limitations. Required feeds could be comprised of plants, invertebrates or even microorganisms. Production will include a variety of filter feeders and benthic detritivores. Although initial consumer acceptance is uncertain, we expect that GM plants will allow the production of seafood with high omega-3 oil content. Finally, there will be the niche market that most consumers associate with current seafood production, which will be limited and expensive. This will consist of growing selectively bred species like salmon on natural oil-rich feeds. We expect the seafood of the future, wild and farmed, to be even more diverse than what is available today.

Climate change will rearrange ocean productivity21, and increasing populations and limitations on terrestrial agriculture9,24,25 will increase our demands on the world’s oceans, with the burden of change largely passed to the poor26. Coastal areas may be abandoned with increased flooding; however, their use for marine and brackish water food production will likely be increased.

The maximum potential of the world’s oceans to feed us is the focus of much current research activity. There are a range of solutions proposed that could be pursued. These include recovering overfished stocks and their productivity3,27, making better use of what we do harvest and reducing waste starting from discarding at sea to spoilage through distribution chains2,23. The scale of response needed requires much more support of the United Nations and other bodies that transcend national limitations as they strive to ensure better adaptation of international instruments such as the Port State Measures Agreement7.

As populations demand more marine-sourced food production and while seafoods remain highly sought-after by wealthy nations choices must and will be made. Markets and society in general will decide which production systems consume finite resources such as water, energy, coastal areas and our essential but ultimately limited wild ocean inputs.