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Add fish poop to the growing list of unlikely allies in the fight against global warming. A new study published in the journal Scientific Reports outlines the critical role small forage fish, in particular northern anchovies, play in burying carbon in the deep sea.
It turns out that small fish like anchovies, smelt and sardines are a major component of the so-called "biological pump" that takes carbon dioxide out of the atmosphere and sequesters it in the deep, where it can no longer contribute to global warming. That pump begins with photosynthetic, carbon dioxide-absorbing, single-celled algae, like the wonderfully intricate diatoms and dinoflagellates, at the ocean surface. Anchovies then feed on the algae, digest it and release it as fecal pellets which sink to the ocean bottom.
At 22 micrograms of carbon per pellet, the contribution might seem inconsequential, but as the study's authors, Dr. Grace Saba of Rutgers University and professor Deborah Steinberg of the Virginia Institute of Marine Science, explain, the cumulative effect on the carbon cycle by large schools of small forage fish could be considerable.
“Our findings show that—given the right conditions—fish fecal pellets can transport significant amounts of repackaged surface material to depth, and do so relatively quickly,” says Saba.
Those "right conditions" are found off of the western coasts of North and South America where cold, nutrient-rich water from the deep upwells along the continental shelf, and subsequently drive the production of enormous schools of small fish and invertebrates. It's these conditions that are responsible for Peru's anchovy industry or California's iconic sardine industry immortalized in Steinbeck's Cannery Row.
But besides delivering carbon to the deep, forage fish also play a critical role in the larger foodweb, feeding whales, dolphins, seals, larger fish and seabirds. For all these reasons it's critical to employ science-based fisheries management to prevent the collapse of this vital resource. Unfortunately, that has not been the trajectory of forage fisheries management in the Pacific. Learn more about forage fish and Oceana's work to conserve these small but invaluable species.