Duluth, MN (KDAL) - Freighters on the Great Lakes posted a busy May, as compared to a year ago, but Iron Ore traffic is down. The Lake Carrier’s Association says cargo movement rose by over three-percent in May versus a year ago. Lakers carried over ten million tons of dry-bulk cargo. Freighters hauled four-point nine million tons of Iron Ore. That’s up slightly from 2012, but is three-percent lower when compared to the long-term average of just over five-million tons between 2008 and 2012. Coal traffic for the month of May was down by over six percent versus a year ago.