Seattle — A group of kayak protesters was taken into custody by the U.S. Coast Guard Monday after attempting to block a Royal Dutch Shell oil rig from leaving port near Seattle. According to Greenpeace, 13 activists including Seattle Councilman Mike O’Brien have been detained, mainly for breaking safety regulations by paddling too close to Shell’s 400-foot Polar Pioneer. Later reports said 24 people were detained.

“That monstrous rig is headed to the Arctic to attempt to do something unconscionable,” O’Brien said in a text message sent from the Coast Guard offices. “I had done everything I know how to do as a citizen, an activist, and as a councilmember to stop Shell from drilling in the Arctic.”

Last month, more than 500 paddlers took to the water when the rig was docked in Seattle’s Elliot Bay, protesting the Obama administration’s tentative approval of Arctic oil drilling.

Protesters have cited concerns over climate change and potential spills. According to High Country News a draft Environmental Impact Statement concludes there is a “75 percent chance of one or more large spills occurring over the 77-year period, and a 25 percent chance of no spills occurring.”

“I am prepared to face the consequences of my actions today,” O’Brien wrote, “because if Shell is successful in drilling in the Arctic, billions of people around the world will suffer from the climate devastation that oil poses to the planet.”

Shell has claimed tapping Arctic oil reserves could add 1 million barrels a day to America’s domestic output, and company spokesman Curtis Smith told the New York Times Shell remains “committed to operating in a safe, environmentally responsible manner.”

Critics of May’s protests say it is hypocritical to demonstrate against oil drilling using plastic boats. Petroleum is an essential component of plastic.

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