American Samoa Mapping Data

coral reef
Map of American Samoa, courtesy of Perry-Castaneda Library Map Collection.

The Territory of American Samoa, which is made up of five rugged volcanic islands and two coral atolls, is the only United States territory south of the equator. American Samoa includes the largest island of Tutuila with a population in excess of 50,000 (including Aunu’u) and a land area of 145 sq. km; tiny Aunu’u Island, immediately southeast of Tutuila; the Manu’a Island group of Ofu, Olosega and Ta’u, which combined have a population of approximately 3,000 and a land area of less than 51 sq. km; Swains Island, a small coral atoll that has a varying population of less than 20; and unpopulated Rose Atoll, which is a wildlife refuge under U.S. Fish and Wildlife Service jurisdiction. The U.S. National Park Service operates the 4,250 hectare National Park of American Samoa located on the islands of Ofu, Ta'u, and Tutuila, with about 170 hectares below sea level; the Fagatele Bay National Marine Sanctuary on Tutuila is a part of NOAA’s National Marine Sanctuaries program.

Nautical chart of Ofu and Olosega Islands overlain with high-resolution multibeam data. Note the lack of soundings in less than 100 fathoms. Click for larger image

Existing nautical charts of Tutuila show surrounding banks (0 to 60 m) with an area of approximately 300 sq. km, but little is known about the coral reef and other ecosystems that exist on these extensive banks. Prior to CRED mapping activities using R/V AHI in spring 2004, no shallow bathymetric information existed around Ofu, Olosega and Ta’u and there are few soundings in less than 200 m (100 fathoms) on the nautical chart. The new bathymetry data show that Ofu and Olosega also have surrounding banks, but they are less extensive than those on Tutuila. In contrast, the precipitous slopes around Ta’u continue uninterrupted into the ocean depths. All these data were collected for benthic habitat mapping but are also being submitted to NOAA’s Office of Coast Survey for evaluation as resources for nautical charting.

Multibeam mapping in 20-250m depths around Aunu’u, Ofu, Olosega, and Ta’u was 95% completed in 2004, and approximately 60% of the banks around Tutuila were mapped. These Tutuila data have been combined with a limited amount of 2001-2002

Multibeam data collected in 2004 around Tutuila, American Samoa and Aunu'u Island. IKONOS imagery from NOS Biogeography. Click for larger image

multibeam data available from Dr. Dawn Wright at Oregon State University and Dr. Dave Naar of University of South Florida. No multibeam data were collected at Rose or Swains Atolls; surveys are planned there in 2006. During cruises in 2002 and 2004, CRED also collected photographic and video data around all islands and atolls; these optical validation data will be used to aid in interpretation of multibeam bathymetry and imagery data.
There are numerous management issues in American Samoa that have already been identified for which these data can be used, including: health of coral reefs; expansion/improvement of harbors and air strips; cable routes and sites for Ocean Thermal Energy Conversion (OTEC) facilities; dredging; and fishing impacts.

Multibeam data can be used to address a wide variety of management needs around Tutuila, American Samoa. Click for larger image
Multibeam bathymetry and towboard tracks (green) around Ofu Island, American Samoa. IKONOS imagery has been draped over USGS 10m DEM. Management issues specific to Ofu are shown in yellow block Click for larger image

Gridded bathymetry data (5m resolution) of Tutuila, Aunu’u, Ofu and Olosega are available for download. Processing of Ta’u bathymetry data is still underway, and data are expected to be available in the near future.