Disemboweled sharks are washing up on the coasts of Africa in large quantities. The cause: Orcinus orcas.

Two orcas, named Port and Starboard, are ruthlessly killing sharks off the coast of South Africa. The duo can be recognized by their twisted dorsal fins and for their high kill count of 20 sharks, according to marine biologist Ralph Watson.

“[17] is the largest number of sharks these orcas have killed in this area in one sitting,” shark researcher Alison Towner said in a CBS article.

Passersby alerted researchers of the situation after mangled shark corpses were discovered on the beach in late February.  It is thought that this behavior started around last year when drone footage recorded Port and Starboard leading four other orcas in the hunting of a great white shark.

The animals’ killing technique is gruesome but precise, targeting the prey’s liver, an organ typically sought after for its nutrition and healthy oils.  However, because only the liver is being consumed, scientists believe the orcas’ twisted fins are a result of the unnatural diet.

“The dead sharks are torn open at the pelvic girdle, they have Orca teeth marks known as rake marks on their pectoral fins and their liver is missing,” Towner said to Phys.org.

The drone footage is fascinating yet concerning for suggesting that Port and Starboard are teaching other orcas their kill tactics. While not a threat to humans, the ecosystem could suffer greatly from these sudden changes, with a dramatic and worrying decrease in the shark population across the coasts of Africa, though extinction is unlikely.

“Two killer whales are not going to wipe out a species,” Sea Search scientist Simon Elwen said to Phys.org.