Vessel Traffic Overview

Updated:October 9, 2009 14:57

Trans-Pacific Vessel Traffic Passing through the Aleutians Subarea

Figure 4 shows the primary traffic routes of vessels on the Northern Pacific great circle route traveling through the Aleutians Subarea. Vessels on this route pass through the Aleutian Island chain twice – once at Unimak Pass and once at a point west of Tanaga Island. Analysis of nine months of data (October 1, 2005 through June 30, 2006) from the recently installed automated identification system (AIS) at Scotch Cap, Unimak Pass reveals that 2,336 vessels, or on average, eight or nine deep draft vessels a day (or an estimated 3,100 vessels per year) used Unimak Pass for trans-North Pacific voyages. AIS data information for each vessel detected provided the vessel name, vessel type, next and last port and call-sign. Therefore, we were able to characterize the type of shipping along this trans-Pacific route. This characterization is presented in Table 2 and Figure 5.

AIS data also reveals that the North Pacific great circle route through Unimak Pass is used primarily by vessels traveling west from North America to ports on the East Asia coast (See Figure 6). Moreover, vessels departing from southwest ports in North America often use Unimak Pass. AIS data shows that 17% of the vessels transiting Unimak Pass were sailing from California.

There is also a more southern great circle route across the North Pacific, as seen in Figure 2. This route passes south of the Aleutians and is generally used for voyages from East Asia to North America. Thus, deep draft commercial ships on trans-Pacific voyages generally follow a counterclockwise trade route from North America through the Aleutians to Asia, then back to North America along routes south of the Aleutians. These trade routes take advantage of the counterclockwise ocean currents in the North Pacific. As a note of interest, the Selendang Ayu had just cleared Unimak Pass enroute to Dalian, China from Seattle when it lost power, eventually blowing aground and breaking up. The Cougar Ace was enroute to Vancouver from Tokyo on the southern great circle route outside of US/Alaska waters when the motor vehicle carrier suffered a catastrophic loss of stability.

The data obtained from AIS does not provide the fuel capacity of the vessels transiting Unimak Pass, nor does Lloyd’s Register. We believe the best indicator of fuel capacity by vessel type can be estimated from the ADEC database of 1608 vessels that have received an Alaska Certificate of Financial Responsibility (See Table 1). Using the AIS data from Unimak Pass collected over nine months and the information on fuel oil capacity by ship type from the ADEC database, the profile for 92% of the ocean-going vessels on international trade passing through the Aleutians on great circle voyages can be characterized as follows:

• Approximately 1,200 container ships (39% of total) per year with a median fuel capacity of 1.6 million gallons of persistent fuel oil;
• As many as 1,300 bulk and general freight ships (41% of total) with a median fuel capacity of approximately 470,000 gallons of mostly persistent fuel oil,
• About 265 motor vehicle carriers per year (8.5% of total) with an estimated average fuel capacity of 500,000 gallons of persistent fuel oil;
• About 110 reefer (refrigerated) cargo ships (3.5% of total) with a median fuel oil capacity of 317,000 gallons of mostly persistent fuel oil.
  

Given the fuel consumption required to reach the Aleutians from an East Asia or North America port, vessels traveling through the Aleutians will carry at least 100,000 to 200,000 gallons less fuel than maximum capacity.

The remaining 8% of the vessels transiting Unimak Pass consist of tank vessels, passenger ships, towing vessels, and other miscellaneous ships. These vessels include 20 to 22 tankers per year, transporting about 400 million gallons of oil.

The North Pacific great circle route intersects the Aleutian archipelago at both Unimak Pass and the western Aleutians. This trade route crosses the transit lanes and fishing grounds of the largest fisheries in North America, which are valued in excess of 1.5 billion dollars. The North Pacific great circle route also passes through the Alaska Maritime National Wildlife Refuge, which is home to 40 million seabirds and numerous marine mammals.