The notion that aquaculture could help reduce overfishing by replacing wild fish consumption hasn’t panned out, according to a new study published in Conservation Biology. In fact, the aquaculture boom in recent years may just be supplementing the amount of fish we eat, while contributing additional environmental impacts.

By looking at data on fisheries changes and consumption patterns in up to 173 countries between 1970 and 2014, the study’s international team of researchers show that, overall, aquaculture has not led to any substantial decrease in wild fisheries.

Only in one of the nine analytical models they applied to the data, did farming fish seem to reduce the pressure on wild fish. In all the rest, despite rapid growth in aquaculture in the last 40-odd years–which is now the fastest-growing food sector in the world–it doesn’t appear to have shifted the focus away from wild fish. “Aquaculture is not taking the place of traditional fishing efforts, or even necessarily reducing them,” says one of the researchers, Stephano Longo.

The findings may come as a surprise to those who view aquaculture as a technical solution to the sustainability troubles facing wild marine fish. This notion–that one less-threatened commodity can replace another more threatened resource, in order to save it–is a common line of thought, the researchers say. “The assumption is that this change diminishes the demand placed on the latter, thus helping to conserve it,” they write in their paper.

But this idea is often flawed. The researchers give an example presented in another 2012 study, which found that using renewable energy sources to replace fossil fuels does not necessarily drive a reduction in fossil fuel use. Instead, it usually just adds to energy consumption, overall.

It seems the same principles are at work in aquaculture–but what’s driving this? Why wouldn’t farmed fish simply replace wild fish–as seems logical, if it’s the same product, but just from another more sustainable source?

While the researchers didn’t explore this in detail in their study, they do speculate that there could be a number of reasons why–some of which have already been explored in other research. The most notable among these is that farming large, carnivorous fish such as tuna requires feed, and that feed comes in the form of wild fish. This links aquaculture inextricably to the deleterious impacts of fisheries out at sea. As well as this, the researchers point out that many aquaculture operations are stocked–at least initially–with wild fish, which could also be increasing pressure on ocean fish.

There are also more nuanced, socioeconomic factors to think about. Fish farmers would be more likely to farm large species like salmon and tuna that fetch a high market price, but these species are also ecologically-intensive because of their feeding needs. Furthermore, by increasing the availability of fish, aquaculture could actually be increasing the global appetite for this commodity. The unintended effect of that could be that it promotes greater consumption of wild fish, as well as farmed varieties.

“Although current aquaculture technologies may have the potential to displace fisheries captures, it appears that production has been structured more toward overall expansion rather than environmental conservation,” the researchers write.

But this doesn’t mean aquaculture can’t still right some wrongs of our global fishing system. Farming fish could shift pressure away from wild stocks, if we do it differently. One approach would be to replace the production of resource-intensive species, like tuna, with more filter-feeding molluscs like oysters and mussels–species that are high in protein, and don’t require fish feed. Another option is to find alternative feeds for fish–such as algae–to reduce the reliance on wild stocks. This is already a developing area of research.

While these changes would require huge infrastructural and socioeconomic shifts, they could ultimately transform aquaculture into what many believe it should be: a tool for fisheries conservation, not just another way of creating more lucrative commodities to sell.

Source: Longo et. al. “Aquaculture and the displacement of fisheries captures.” Conservation Biology. 2019.

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