Authors: Douglas Burn and Aaron Poe | Aleutian and Bering Sea Islands Landscape Conservation Cooperative (ABSI LCC)
The shortest distance between any two points on a spherical object (such as the Earth) is known as a “Great Circle Route.” The North Pacific Great Circle Route that connects the west coast of the United States with major ports in Asia transits directly through the Aleutian archipelago. Each year, several thousand large, deep-draft vessels make this voyage, sailing through Unimak Pass on the eastern end of the Aleutians, and using one of several different passes to the west.
For the most part, this vessel traffic occurs without incident. In early December 2004 however, the cargo vessel Selendang Ayu lost power in the eastern Bering Sea and driven by high winds and rough seas, drifted southward before running aground on Unalaska Island. This incident, which resulted in the loss of the vessel, cargo, fuel, and the lives of six crew members, represents the worst-case scenario for vessels transiting through the Aleutians.
Over the past decade, the Marine Exchange of Alaska (MXAK) has developed a land-based network of receivers that monitor signals broadcast by AIS (Automatic Identification System) transponders. AIS is required for most vessels greater than 300 tons and are becoming more common on other types vessels. At present, the westernmost AIS receiver in the Aleutians is located at Adak Island, and is incapable of monitoring vessel traffic at the western ends of these routes. More recently, satellites have been launched that can receive AIS data. These satellite systems typically do not receive vessel locations with the same temporal frequency as AIS receivers on the Earth’s surface. Instead, they offer broader spatial coverage that is not limited by the fixed location of land-based receivers.
Analysis of data collected by the MXAK network indicates that there were 4,615 transits by deep-draft vessels through Unimak Pass in 2012. The routes used by these vessels at the western end of the Aleutian archipelago remains a mystery. In 2013, the Aleutian and Bering Sea Islands Landscape Conservation Cooperative (ABSI LCC) partnered with the Wildlife Conservation Society (WCS) and the Scenarios Network for Alaska and Arctic Planning (SNAP) to purchase and analyze a three-year archive of satellite AIS data. Preliminary results indicate that vessels transiting through Unimak Pass primarily enter/exit the Bering Sea on one of three routes (Figure 1).
Two of these routes pass close to islands in the Near Island group at the western end of the archipelago. In addition to the three main routes that transit through the Bering Sea, there is also a fourth route south of the Aleutians that makes its closest approach near the center of the archipelago near the Delarof islands. Field Biologists frequently observe large container ships passing within a few miles of shore in the Aleutians (Photo).
Results of this study will have a number of applications, including the formulation of vessel routing recommendations that provide greater distance and safety from possible vessel groundings like the Selendang Ayu.
For more information about this project, visit the ABSI LCC web site.
Header Image:Japanese steamship Borneo Maru in Gertrude Cove. Photo by C. Funk. 6/13/2014.