Police spokesman Roland Eckers said in the Netherlands that the arrests included the captain of the Greenpeace vessel Rainbow Warrior III, Tim Willcox.
“The captain has been arrested and the ship is being taken elsewhere else,” Eckers said.
He added that 30 others were arrested for trespassing or using inflatable boats to prevent the Russian tanker, Mikhail Ulyanov, from docking in port.
According to Greenpeace, 80 activists were involved in the protest.
One group of activists painted “No Arctic Oil” on the hull of the tanker.
Other activists in inflatable dinghys tried to prevent the ship from docking by putting themselves between the tanker and the port wall.