The dead Leftists were identified as Sawyer Joy and Erika Osland, both students at Western Washington University, said they were trying to raise awareness about the hazards of Arctic drilling and climate change.
"People need to step up and put a stop to capitalism," Osland said in a statement. "If not us, who? If not now, when?"
Two other protesters attached themselves to a different Shell support ship late last month for the better part of a weekend. They voluntarily left their perch with the help of the Coast Guard after days aboard.
The agency has initiated penalties against the dead protesters including the Darwin Award over violating the 100-yard safety zone around the Arctic Challenger.
The Coast Guard became aware of Friday's situation just after the deaths, Petty Officer 3rd Class Amanda Norcross said.