How Fish Poop Can Help the Climate

There’s a new climate solution on the rise. It’s all the rage. Are you ready?

Fish. In the ocean. And their poop.

Huh? How could fish possibly remove enough carbon to have an effect on the climate? The secret is in the numbers. The ocean is a huge place, and healthy fish populations filling it up do have a significant effect on the climate. In fact, according to a new study led by researchers at UCLA, the role that fish and their feces play in storing carbon is vastly underrated.

Carbon in Air and Sea

A carbon sink is a place where organic matter (containing carbon) sits for long periods of time. An old-growth forest is a carbon sink. Fossil fuels are a carbon sink when they are left in the ground. The process of incorporating carbon into a sink is called sequestration. When fish go about their business, eating and pooping, their waste falls to the ocean floor. It mixes with the sediments, and stays there.

About a quarter of the carbon dioxide that comes from human’s emissions ends up in the ocean. This carbon is incorporated into plankton, which are eaten by bigger plankton, then small fish, then bigger fish. The big fish produce large sinking turds. When the poop reaches the ocean floor–as long as it isn’t disturbed by destructive practices like trawling or dredging– it stays there for a long time.

Threats to Ocean Carbon

Large-scale commercial fishing poses a threat to this major carbon sink. By removing fish, we are removing a source of poop. Not only does fishing prevent further carbon sequestration, but the harvested fish release some of the carbon in their bodies back into the atmosphere.

When fish die naturally, their bodies fall to the seafloor and integrate into the deep-sea ecosystem. They feed all the strange-looking critters you see in nature documentaries. The largest animals on earth, whales, become a huge carbon sink when they die. Their bodies fall to the seafloor and nourish the deep sea for weeks, months, or even years.

Before humans hunted whales to their current low numbers, the gentle giants played a crucial role in nutrient cycling in the ocean. They consumed 430 million tons of krill every single year— that’s twice the current amount of fish catch by weight from the entire world. This food, now uneaten, caused the collapse of these food webs. If we can bring the whales back, we might be able to bring back these ecosystems and restore their carbon-storing capabilities.

What Can We Do?

When there are tons of carbon swimming around in fish, whales, and their poop, there is less floating around in the atmosphere, warming the planet. So what can you do to keep the fish around? You don’t need to stop eating fish altogether, but consider eating sustainable seafood. There are multiple groups that evaluate sustainable fisheries. They look at the health of the populations they came from, any side effects of the fishing method, and benefits to the communities that harvest them. The Monterey Bay Aquarium produces a great guide to what fish are considered sustainable, and they have an app that you can bring to dinner with you! The ocean and the atmosphere will thank you.

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