MEXICO CITY — Mexico vowed to keep looking for a mysterious island that could extend its offshore oil claims after university researchers said they couldn't find it. "The island doesn't exist" in the area where it was shown on maps, a National Autonomous University of Mexico study concluded after conducting studies with underwater sensing devices and aerial reconnaissance in the area. "Isla Bermeja" appeared on maps from the 1700s as a speck of land off the northwest coast of the Yucatan peninsula. A group of Mexican legislators hoped the island would help their decade-long effort to fend off what they...