Gunmen boarded two fishing vessels just off the coast of Nigeria and took two people hostage, security sources said on Saturday, the latest in a series of hijackings in the waters around Africa’s largest oil business. The captains of the two boats were taken early on Friday, the same day eight pirates took three hostages from an oil supply vessel contracted by Chevron Corp, two security sources close to the incidents said. Chevron confirmed the attack on the vessel owned by its contractor, the second hijacking on ships hired by the U.S. major off the coast of Nigeria this month