The first category results from the substantial and growing maritime trade between the United States and Asia. Many of the vessels trading between northern Asia and the northern Pacific Coast ports of the United States and Canada follow the Great Circle Route through Unimak Pass at the eastern end of the Aleutian Islands chain. The pass is just west of Unimak Island, 1,300 miles west of Juneau and 800 miles southwest of Anchorage. The vessels involved in this trade are a mix of large commercial ships classed as containerships, bulk carriers, car carriers, tank vessels, and others. They are mainly foreign-flagged and on innocent passage through these waters.
Weather, distance, and other factors combine to influence the most efficient route chosen by shippers when voyages are planned. According to the latest tracking data available (discussed in detail below), about 4,500 large commercial vessels transit Unimak Pass annually. About 3,600 of these vessels are westbound because the majority of eastbound vessels follow more favorable currents by using the route south of the Aleutians. Although similar tracking data are lacking for the southern route, it is assumed for present purposes that the number of vessels traveling in each direction is equal; thus the total number of large commercial vessel transits in both directions would be about 7,200 annually.
The second category of vessels of interest to a risk assessment of Aleutian shipping operations includes local fishing vessels and supply, work, or service vessels calling on Alaskan ports. Vessels in this category are smaller than those in the first category, carry less fuel and cargo, are typically on shorter voyages, and are usually of U.S. registry. For example, 400 to 500 fishing vessels operate in and around the Aleutians.1 Also in this category are numerous ferries, cruise ships, tugs, and barges. Fishing vessels operate mainly out of Dutch Harbor; local tug–barges, small cargo vessels, and work boats operate out of either Dutch Harbor or other, smaller Aleutian ports in addition to making up some north–south traffic to and from more distant Alaskan locations.