Why farming fish is less sustainable than catching it in the wild

It has been argued that fish farming is a sustainable food source that helps feed the growing world population while protecting wild fish populations, but this is not true.

“Aquaculture is not a substitute for harvesting wild fish from the ocean,” says Matthew Hayek of New York University. “In fact, it relies on catching wild fish from the ocean.”

Hayek and his colleagues showed that the amount of wild fish killed to feed farmed fish is 27 to 307 percent higher than previous estimates.

According to Hayek, farmed carnivorous fish eat wild fish caught in the ocean at several times the weight of their farmed counterparts. For example, producing 1 kilogram of salmon may require 4 to 5 kilograms of wild fish.

However, while the demand for farmed fish is increasing, the amount of wild fish caught is not increasing. “In multiple fisheries, we are moving towards a scarcity of fish in the ocean,” Hayek says.

As a result, as the aquaculture industry expands, an increasing proportion of the world’s wild fish catch is used as feed for farmed fish.

This means people in places like Southeast Asia and West Africa can no longer afford to buy fish, because fish is highly valuable as a source of fishmeal and fish oil for farmed fish, said Patricia Majluf, a team member at conservation group Oceana. says.

Increasing the proportion of plant-based products in the diet of carnivorous fish, or raising omnivorous or herbivorous fish such as tilapia, carp, or catfish, creates another set of problems. Feeding fish with human-edible plant-based food requires more land and water to produce fish food, leading to problems such as deforestation.

“These sectors are growing rapidly, so we are now supplying them with several times more crops from land than before,” says Hayek.

“As long as you’re eating animals, you’re not immune to some kind of shock somewhere,” he says. “Raising animals requires more resources to nurture and grow their bodies than can be obtained by eating them. It’s a basic fact of biology.”

But farmed shellfish, such as mussels, which are eaten by filtering seawater, are far more sustainable, he says.

There are several 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 past estimates. For one thing, Hayek said the team used a wider range of sources than previous studies, meaning there is less chance of statistical bias.

The researchers also counted all the fish used to produce fishmeal and fish oil, as well as those caught to feed farmed fish.

Finally, the researchers also estimated the number of fish that were killed but not brought to market. Unwanted species are often discarded from fishing vessels, but usually do not survive. Sometimes they leave the seine slightly open to let unwanted fish escape, but they often get injured and die.

Even ignoring these additional deaths, the conclusion remains that the amount of wild fish killed to feed farmed fish is higher than previously estimated, Hayek said. But counting them adds 20 to 50 percent to the total, he says.

“The use of fishmeal and fish oil in aquaculture has proven to be more complex than many industry analysts expected,” said Stefano Longo of the University of Gothenburg in Sweden. “Fishmeal and fish oil inputs in aquaculture systems are likely to be underestimated, perhaps significantly.”