A nonprofit group called Shark Allies says that supplying a global COVID-19 vaccine could cost the lives of 500,000 sharks. Shark livers contain an oil called squalene that is a preferred adjuvant, or added substance, used in vaccine preparation to boost immune response.

According to the Miami Herald, the amount of squalene required to formulate enough vaccines to protect people around the world would wipe out many shark species. While scientists could manufacture a similar adjuvant using non-animal alternatives, these sources are more costly and take longer to produce.

“Using sharks in COVID-19 vaccines is short-sighted, unpredictable, and unsustainable. There are better alternatives,” Shark Allies wrote in a petition the group is circulating to save the sharks. An estimated 2.7 to 3 million sharks are currently killed annually for their squalene, which is used in cosmetics, as well. The nonprofit group said 22,000 sharks could be slaughtered to supply the U.S. alone with COVID-19 vaccines, once a candidate is developed and approved.

Squalene has been used as a component in other coronavirus treatments, according to the Herald, which suggests it could also be effective in a COVID-19 vaccine.

“As a result, the demand for shark squalene could skyrocket, leading to a significant increase in the killing and harvesting of sharks for their livers,” said Shark Allies.

Other species have also been tapped to help develop the COVID-19 vaccine. The blood of horseshoe crabs is used to detect toxins and other harmful agents in vaccines and overharvesting could also significantly reduce their numbers.