Fish Farms Kill Billions More Wild Fish Than Previous Estimates, Study Finds

Fish, once a Friday penance for many, has recently become the “good meat” poster child. Fish farming has been touted as a way to help protect wild marine animals and, by some, even a way to feed the world. Yet a new study in Science Advances makes the case that farming fish comes at a much higher cost than previous estimates suggest, because of how much aquaculture relies on wild fish. According to the researchers, the total mass of wild fish required to produce farmed fish could be 536 percent higher than previous estimates. The drain on wild fish populations can in turn make it harder for vulnerable communities to find food. One of the core arguments for farmed fish — the idea that it protects wild fish by leaving them in the sea — ignores the fact that aquaculture relies on feed made from wild anchovies, sardines, herring, mackerel and other fish that many coastal nations rely on for sustenance.

The field of fish farming is no stranger to criticisms: overcrowded pens; poor fish health; inhumane killing methods; pollution; plastic waste from nets used to create pens, as well as diseases (spread by escaped farmed fish) that cause health problems for wild fish populations.

Nonetheless, the practice is growing. Farmed fish production is expected to have expanded by over 17 percent between 2022 and 2032, according to the United Nations Food and Agriculture Organization. By 2050, global demand for fish is expected to nearly double, thanks in part to an ever-increasing output of farmed seafood. Over a similar period, demand for fishmeal — the feed carnivorous farmed fish like salmon, trout and bass rely on — is projected to grow over seven percent by 2030.

“This is a hot topic in academic circles, but I don’t think the public understands how fish farming works, especially in terms of its reliance on wild fish,” Spencer Roberts, an environmental science and policy researcher at the University of Miami and a co-author of the new study, tells Sentient. In reality, says Roberts, aquaculture has simply shifted pressure from one set of fish to another.

The need for fish feed is creating problems for people too. “When we hear about fish farming feeding the world, it’s not true. The reality is that it’s starving people…in places like West Africa where ‘reduction fisheries‘ are taking their fish,” says Roberts, and selling or using them to turn into fishmeal. “Subsistence fishing communities are literally starving and being forced to emigrate,” Roberts adds.

Part of how the aquaculture industry sold itself as the more sustainable option is thanks to what’s known as the fish-in-fish-out ratio — the measurement of how many wild fish it takes to feed farmed ones. This figure, in essence, compares the number of how many wild fish are used as feed for fish farming, versus how many come out to feed humans. The calculation is used by the industry to demonstrate its efficiency, and therefore, its sustainability. It’s used to make the case for how large a role it should play in a future with a growing global population, increasing planetary warming and shrinking natural resources, like farmland to grow food.

By focusing only on the ratio, Roberts and his co-authors argue, the true number of wild fish used to feed farm ones ends up obscured — indirect deaths are ignored, essentially — while outputs are maximized. This creates a misleading measurement.

There are a number of ways this plays out, but here’s one example: so-called fish trimmings. Trimmings, which are the parts of the fish people don’t traditionally eat (heads, tails and so on), are conventionally classified as by-products and subtracted on the basis that they are not wild fish. But according to a representative from The Marine Ingredients Organizations, only about 20 percent of trimmings for fishmeal come from farmed fish. The other 80 percent is from wild fish.

Once you adjust the calculation for the fish trimmings and other factors, the study finds, the volume of wild fish used to feed farmed fish could be over 300 percent higher than standard estimates. Taking other factors into account — when farmed fish that don’t eat fishmeal are excluded, and indirect mortalities like slippage are included — it’s even more dramatic. The total wild fish mass, according to the study, could be 536 percent higher.

It is not yet possible to convert the study’s new percentage estimates into wild fish numbers, but Roberts says researchers working on the question believe reduction fisheries account for most fish taken from the ocean each year, killing over a trillion wild animals. These are animals who could otherwise be maintaining ocean health simply by staying in the sea, or helping to feed vulnerable populations.

Responses from fishmeal trade bodies to the new study varied, with the Marine Ingredients Organization favoring “a shared metric system” of lifecycle assessments, rather than fish-in-fish-out, and linking to a study that supports these as “the pathway to improved sustainability for all feed ingredients.” A life cycle assessment quantifies the environmental impacts of a product, system or service from beginning to end.

The Federation of European Aquaculture Producers’ general secretary Javier Ojeda was more upbeat about the study, saying its average ratio confirms that farming of fish reliant on fishmeal “is a net producer of aquatic food [which] should be heralded as great news,” rather than a way to “demonize” it.

The Problem with Dewilding the Ocean

Fish farming creates another problem: dewilding. Separately, another new study finds mariculture — fish farming that takes place in the sea — is contributing to oceanic dewilding. Dewilding is a term for prioritizing human interests over ecosystems and, essentially, destroying the natural or wild world. Fish farms pollute the ocean too, with fish feces and uneaten food from farms creating excess nitrogen and phosphorus that can lead to algae blooms, depriving the water of oxygen.

The study looks at different dewilding categories, one of which is conceptual dewilding. Conceptual dewilding is a category that deals with human perceptions, which can set the stage for uncontrolled exploitation, says Becca Franks, co-author and assistant professor of environmental studies at New York University.

“The ocean is less explored than the moon… [but] as we map it for more places to put farms in and start to see it as a place to extract more resources from, the less we see it as a wild place, and the more we are going to be casual about destroying it,” Franks tells Sentient.

Findings by Roberts and his team that aquaculture’s dependence on wild fish is underestimated, are, Franks says, an example of “this rough, casual” approach to marine environments, and evidence that we are “not looking at the ocean as a wild space that should be approached with respect and caution.”

Franks offers an example of humanity turning from a rough approach to a respectful one: whales. “We used to see them as floating oil reserves …[but] with enough organizing and attention to who they actually were … and allowing a bit of poetry to come in … [we have] completely changed the way we think about whales, and it has allowed them to do better.”

The bottom line, according to Franks, is that the critical role of oceans in storing carbon and mitigating climate change means we should take a very careful look at what kinds of aquaculture we want to proceed with, adding, “the details really matter.”

Clarification: This piece has been updated to attribute a calculation to The Marine Ingredients Organisation and to include only the precise percentage figure derived from the study.