Analysis: Invaders in Ships’ Ballast Tanks

With an estimated 162 non-native species causing billions of dollars in damage in the Great Lakes, Michigan is considering requiring maritime shipping companies to get permits to dock at ports in the state. Michigan would be the first state to require ballast-water permits on the Great Lakes.Ballast water used to stabilize a vessel to keep it from bobbing in open water often carries alien species that compete with and can replace native fish and plants.