Mariana Islands Mapping

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Cruise Track of NOAA Ship Oscar Elton Sette in the Mariana Archipelago in 2003

The 290-km long Mariana Islands Archipelago encompasses 15 islands of the U.S. Commonwealth of the Northern Mariana Islands and the U.S. Territory of Guam, as well as numerous offshore banks. The islands can be divided into two groups geologically: the older southern island arc that includes Rota, Tinian, Saipan and Farallon de Mendinilla and the younger, volcanic northern islands. Though the southern islands are volcanic in origin, they are nearly all covered with uplifted limestone from ancient coral reefs; these uplifted limestones create a flat “layer-cake” topography with numerous caves, both above and below sea level.

The southern islands have the oldest and most developed reefs in the Mariana Islands. The reefs are generally most developed on the western (leeward) sides of the islands. The majority of the Archipelago’s 244,000 residents live on four islands: Rota, Tinian, and Saipan, and Guam. The geologically younger northern islands, Anatahan, Sarigan, Guguan, Almagan, Pagan, Agrihan, Ascuncion, Maug and Uracas are primarily made up of very recent (4,000 year-old) volcanic materials. A permanent community of seven lives on Agrihan Island. The extent of reefs around these islands is varied. In general, the younger, more northerly Mariana Islands have sparse, low diversity coral reef communities. Around only a few of the northern banks and islands (e.g. Maug, Guguan, Stingray Shoals), diverse coral communities with as many as 60 coral species have been observed.

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Sasanhaya Marine Protected Area Rota, CNMI

A variety of resource management issues are present within the Mariana Archipelago. Anthropogenic effects are major concerns in the southern populated islands and the local governments are working to resolve these problems. CNMI and Guam have12 MPAs or Preserves, many of which have been established in the last decade.

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Multibeam data collected by R/V AHI is displayed over existing nautical chart. Note anchorage circles in red. A reconnaissance survey of the channel and dredged harbor (upper right) was also conducted at the request of the Commonwealth Port Authority. These data were submitted to NOAA's Office of Coast Survey for evaluation for charting purposes.

Fishing pressures are strong, especially on the banks near populated areas. Defense activities raise other issues. The U.S. Navy routinely anchors large, prepositioned ships off Saipan. It is not clear what type of habitat exists in the area or what the impact of frequent anchoring might be. In this same area the channel leading to the main anchorage is of concern due to depths in the channel that are shallower than those shown on the existing nautical charts. The Navy also uses the island of Farallon de Mendinilla as a bombing range. The poorly charted banks adjacent to this island are a prime fishing ground when vessels are allowed into the area. In addition to these human pressures, severe storms and active volcanism have impacts on coral reef ecosystems.

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Bathymetric map of Pathfinder Bank made from single-beam soundings in meters taken aboard the NOAA vessel Oscar E. Sette. Single-beam bathymetric maps are also available for Arakane and Zealandia Banks. Not to be used for navigation.

Shallow-water (0 to 30 m) benthic habitat maps of the Archipelago are being prepared by NOS. Recent CRED work extends this work to greater depths by using sonar to produce high-resolution maps of the seabed and by collecting critical optical data required for ground truthing. During cruise OES0306, shipboard mapping work throughout the Archipelago included single-beam sonar and bottom classification tracks. During that 40-day deployment, approximately 244 km2 of seabed was surveyed and 126 towed camera transects were conducted.

Shallow-water (0 to 30 m) benthic habitat maps of the Archipelago are being prepared by NOS. Recent CRED work extends this work to greater depths by using sonar to produce high-resolution maps of the seabed and by collecting critical optical data required for ground truthing. During cruise OES0306, shipboard mapping work throughout the Archipelago included single-beam sonar and bottom classification tracks. During that 40-day deployment, approximately 244 km2 of seabed was surveyed and 126 towed camera transects were conducted.

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Oscar E. Sette, NOAA Vessel. Photo by Robert Shroeder

The R/V AHI was deployed from the Sette in Saipan Harbor and worked independently around Saipan, Tinian, Rota, and Guam during the cruise period. Gridded bathymetry data are available for download The bank tops and shelf environments of Saipan and Tutuila, as well as the offshore banks of Marpi and Tatsumi, were completely characterized in water depths ranging from 20 to 250 meters. Approximately 20% of the banks and shelf environments of Rota were surveyed, including the seabed adjacent to the main village and the Sasanhaya MPA. Approximately 15% of the banks and shelf environments of Guam were also surveyed, including the Pati Point Marine Preserve.

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High-resolution bathymetry coverage around N. Guam