NEW ORLEANS (AP) — Engine troubles aboard a federal research ship have forced the cancellation of this year's survey of the low-oxygen "dead zone" that forms each summer in the Gulf of Mexico. Nola.com ' The Times-Picayune (http://bit.ly/2akva1q ) reports that the cruise was expected to determine whether researchers were accurate in June in estimating that this year's low oxygen area in the Gulf of Mexico would cover 5,898 to 6,824 square miles.