It has been claimed that the fish agriculture is a sustainable source of food that will help us feed the world’s growing human population while protecting wild fish populations – but that’s not true.
“Fish farming is not a substitute for catching wild fish from the ocean,” says Matthew Hayek at New York University. “It actually depends on catching wild fish in the ocean.”
Hayek and his colleagues showed that the amount of wild animals fish killed to feed farmed fish is between 27 and 307 percent higher than previous estimates.
Farmed carnivorous fish eat several times more weight than wild fish caught in ocean than what you get by growing them, says Hayek. For example, producing a kilo of salmon may require 4 or 5 kilos of wild fish.
But wild fish catches are not increasing in line with growing demand for farmed fish. “For many fisheries, we are heading toward a shortage of fish in the ocean,” says Hayek.
The result is that as the aquaculture industry expands, an increasing proportion of the world’s wild fish catch is destined for farmed fish.
This means that people in countries like Southeast Asia and West Africa can no longer afford fish because it is more valuable as a source of flour and of fish oil for farmed fish, explains a member of the team. Patricia Majluf to the conservation organization Oceana.
Increasing the proportion of plant-based products in the diet of carnivorous fish, or breeding omnivorous or herbivorous fish – such as tilapia, carp and catfish – creates another set of problems. If plant-based foods that could be eaten by humans are fed to fish, more land and water will be needed to produce fish food, leading to problems such as deforestation.
“Because these sectors are growing so quickly, we are now feeding them several times more crops than before,” says Hayek.
“You can’t escape impacts somewhere as long as you’re eating animals,” he says. “Raising animals requires more resources to raise and develop their bodies than can be obtained from eating them. This is a fundamental fact of biology.
But farmed shellfish like mussels, which feed by filtering seawater, are much more sustainable, he says.
There are a number of reasons why Hayek’s team’s estimate of the amount of wild fish needed to produce a given amount of farmed fish is much higher than previous assessments. The first is that the team used a wider range of sources than previous studies, Hayek says, which means it’s less likely that there is statistical bias.
The team also counted all fish used to produce fish meal or oil, not just those caught to feed farmed fish.
Finally, the team also estimated the number of fish killed but not released to the market. Undesirable species are often discarded from fishing boats but usually do not survive. Seine nets are also sometimes left slightly open to let unwanted fish escape, but they are often injured and die.
The conclusion that the amount of wild fish killed to feed farmed fish is higher than previous estimates remains valid, even when not accounting for these additional deaths, Hayek says. But counting them adds between 20 and 50 percent to the total, he says.
“They show that the use of fishmeal and fish oil in aquaculture is more complex than many industry analysts have estimated,” says Stefano Longo at the University of Gothenburg in Sweden. “Inputs of fishmeal and fish oil into aquaculture systems have probably been underestimated, perhaps even to a large extent.”