| Ships
carry more than 80% of the world’s goods on more
than 45,000 commercial vessels (8).
Most of these ships carry ballast water, which is used to maintain
stability and reduce stress on the hull when cargo holds are not
full. Different
size vessels carry different volumes of ballast water, but large
ships may carry more than 200,000 m3 of water (9). Ships release
ballast
into
U.S. waters at a rate of 2 million gallons per hour (10).
When ships take up ballast water, they also take up aquatic organisms and suspended sediment. Ballast water may contain a variety of organisms including plankton, nekton, fouling, and benthic organisms at various life cycle stages. Bacteria and viruses may also be present in ballast water. Ballast water transports more than 3,000 species of plants and animals each day (9). When the water is released at the destination port, all of the organisms are introduced into the environment. |
 |
|||
| International trade leads to a high rate of nonindigenous species introductions. The Great Lakes/St. Lawrence Seaway, completed in 1959, facilitates international trade. The Seaway runs from the Gulf of St. Lawrence in the Atlantic Ocean to Lake Superior. The total amount of shipping on the Great Lakes is over 180 million tons each year (Northeast Midwest Institute). Since the opening of the Seaway,To reduce the risk of introduced species, vessels must manage their ballast water through exchange or treatment. | ||||
  |
||||
