UCLA researchers found that over 11,400,000 km2 are potentially suitable for fish and over 1,500,000 km2 could be developed for bivalves. Both fish and bivalve aquaculture showed expansive potential across the globe, including both tropical and temperate countries. However, as would be predicted by metabolic theory, many of the areas with the highest GPI were located in warm, tropical regions. The total potential production is considerable: if all areas designated as suitable in this analysis were developed (assuming no further economic, environmental or social constraints), they estimate that approximately 15 billion tonnes of finfish could be grown every year—over 100 times the current global seafood consumption.
Ocean aquaculture is already the fastest-growing food sector, but a lot of work remains to reach its vast potential. There are a few difficult barriers to overcome. In some countries, including the United States, a network of regulations makes it challenging to establish even a single farming operation, the researchers said. In other places, lack of regulation leads to environmental destruction — concentrated waste from poorly managed or designed operations can severely pollute waters and coastal areas.
Also, ocean aquaculture needs to compete in the marketplace and turn a profit, and farming in the open ocean is trickier than doing so close to shore, requiring extra investment. “It takes some engineering to be able to withstand waves and currents,” Gentry said. “The offshore environment can be a pretty brutal place. Having strong infrastructure is taking some time to get going.”
Drawing on the findings of the paper, which maps the global potential of aquaculture, a mere 0.025 percent of the world’s oceans could satisfy global demand for fish, which is at an all-time high. An area of prime locations the size of Lake Michigan could theoretically provide as much as all of the world’s wild-caught fisheries combined.
For fish, they assumed that each square kilometer would contain 249,000 cubic meter of cages, each stocked with 20 juveniles per cubic meter. This low stocking density would result in a density at harvest of approximately 11 kg per cubic meter, which provides a conservative production per unit area estimate. For reference, the European organic standard maximum density is 15 kg per cubic meter for most marine finfish. Farming densities for some marine fish can be up to or beyond 30 kg per cubic meter at harvest. If a stocking density in this range was used, the production per unit area estimates in this study would nearly triple.
For bivalves, they based their design on the offshore longline growing of mussels, and assumed 100 long lines placed in each km2 of the growing area. Each longline would have approximately 4,000 meters of fuzzy rope, and each foot of fuzzy rope would be seeded with 100 bivalves. The space required for anchoring would vary with depth and design, and was therefore not included in this analysis. They acknowledge that farm designs vary significantly and could be adjusted to meet local conditions; however, a uniform design allowed us to most clearly differentiate between areas on a global scale. The production per unit area per year was calculated by dividing the total farm output by the number of years between stocking and harvest. This was based on the assumption that re-stocking would happen immediately post-harvest.
Marine aquaculture presents an opportunity for increasing seafood production in the face of growing demand for marine pro-tein and limited scope for expanding wild fishery harvests. However, the global capacity for increased aquaculture production from the ocean and the relative productivity potential across countries are unknown. Here, we map the biological production potential for marine aquaculture across the globe using an innovative approach that draws from physiology, allometry and growth theory. Even after applying substantial constraints based on existing ocean uses and limitations, we find vast areas in nearly every coastal country that are suitable for aquaculture. The development potential far exceeds the space required to meet foreseeable seafood demand; indeed, the current total landings of all wild-capture fisheries could be produced using less than 0.015% of the global ocean area. This analysis demonstrates that suitable space is unlikely to limit marine aquaculture development and highlights the role that other factors, such as economics and governance, play in shaping growth trajectories. We suggest that the vast amount of space suitable for marine aquaculture presents an opportunity for countries to develop aquaculture in a way that aligns with their economic, environmental and social objectives.
To characterize aquaculture’s potential, they used a three-step approach.
1. They analyzed the relative productivity for each 0.042 degree2 patch of global ocean for both fish and bivalve aquaculture. To do this, they constrained the production potential for each of 180 marine aquaculture species (120 fish and 60 bivalves) to areas within their respective upper and lower thermal thresh-olds using 30 years of sea surface temperature data .
They then calculated the average (multi-species) growth performance index (GPI) for each patch for all suitable fish and bivalve species, resulting in a spatially explicit assessment of the general growing potential for each aquaculture type. GPI is derived from the von Bertalanffy growth equation and uses species-specific parameters (growth rate and maximum length) to create a single metric to describe the growth potential of a species. GPI has been used frequently to assess growth suitability for culture and is particularly useful for fed species or those not subject to food limitations. Locations with a high GPI are expected to have better growth conditions for a spectrum of aquaculture species and, thus, are well suited to development. Using a multi-species GPI average to assess growth potential provides a more general growth suitability metric than is possible when making detailed assessments for a single species. This approach is especially useful given the fast rate at which new species are being developed for aquaculture and the shift in focal species between nearshore and offshore cultures. Moreover, using GPI averages across species provides a conservative assessment, since we are considering an average rather than the maximum growth potential.
2. Once the production potential was determined, we removed unsuitable areas with certain common environmental or human-use constraints. We excluded areas with unsuitable grow-ing conditions due to low dissolved oxygen (fish only) and low phytoplanktonic food availability (bivalves only). They also eliminated areas at over 200 meters depth because they are generally too deep (and thus expensive) to anchor farms, and areas already allocated to other uses, including marine protected areas, oil rigs and high-density shipping areas.
Advancing technology may alleviate some of these constraints through innovative farm designs that allow for deeper mooring and submerged farming structures.
3. They estimated the idealized potential production per unit area by con-verting the average (multi-species) GPI into biomass production, assuming a low stocking density is used and the farm design is uniform across space.