Scientists on the NOAA Ship Hi'ialakai are completing critical seafloor mapping at Penguin Bank in the Hawaiian Islands

April 19, 2006

The NOAA Ship Hi'ialakai is at now at sea creating maps of the seabed over Penguin Bank, a prominent underwater feature in the main Hawaiian Islands. The resulting high-resolution maps of ocean depth, or bathymetry, of the area will provide information critical for marine conservation and management in Hawaii. Federal and State agencies responsible for managing fisheries, conserving marine habitat, recovering protected species, and maintaining healthy ecosystems in the Hawaiian Archipelago require reliable information about seafloor depth and other physical characteristics of the marine environment.

The Hi'ialakai expedition is a collaboration involving several agencies. NOAA partners include the Pacific Islands Fisheries Science Center (PIFSC), the National Marine Sanctuaries Program (NMSP) and the Office of Coast Survey. Other participants include the U.S. Fish and Wildlife Service and the University of Hawaii's School of Ocean and Earth Science and Technology. The bathymetric mapping surveys are under the direction of co-Chief Scientist Joyce Miller, a NOAA-University of Hawaii Joint Institute of Marine and Atmospheric Research oceanographer working with the PIFSC Coral Reef Ecosystem Division, and Susan Vogt (NMSP).

Penguin Bank, located off the southwest tip of the island of Molokai, is an important, extensive shallow marine habitat. It is a fishing ground for Hawaii bottomfish vessels and is also part of the NMSP Humpback Whale National Marine Sanctuary.

The bank will be surveyed using advanced multibeam sonar equipment (echosounders) to measure ocean depth along selected transects, providing complete coverage of the ocean bottom. Multibeam sonars will be deployed from the Hi'ialakai and the research vessel AHI (Acoustic Habitat Investigator) a, 25' survey boat launched from the Hi'ialakai. The Hi'ialakai has two multibeam echosounders. The EM300 is a 30 kHz sonar for use in deep waters (50-5000 m range) and the EM3002D is a 300 kHz sonar for work in shallower areas (20-150 m range). The AHI is equipped with a single Reson 8101ER sonar operating at a 240 kHz frequency for use over a depth range of 10-300 m. During the surveys, OCS personnel will update and refine calibrations of the multibeam sonar equipment on both vessels and work to improve the integration of survey operations across various NOAA offices. The cruise will enable improved coordination in mapping operations among various NOAA offices.

A 3-dimensional image of NE portion of Penguin Bank, mapped in 2005.  Depths range from 20-150 m.  Dark blue denotes deep waters, 
    and lighter shades of green and yellow identify shallower water above Penguin Bank.  The white area to the right is the SW tip of 
    Molokai.
A 3-dimensional image of NE portion of Penguin Bank, mapped in 2005. Depths range from 20-150 m. Dark blue denotes deep waters, and lighter shades of green and yellow identify shallower water above Penguin Bank. The white area to the right is the SW tip of Molokai.
(Click here for higher resolution).

The NOAA multibeam mapping program has already surveyed extensive areas around the main Hawaiian Islands. The survey of Penguin Bank began in 2005 but was not completed. The partial mapping of Penguin Bank, however, was quite revealing. The bank was originally thought to be rather featureless, but a detailed map based on the multibeam sonar data showed several interesting features.

The main objectives of the current Hi'ialakai expedition are to finish the survey of Penguin Bank and re-calibrate the multibeam sonar instruments. If the work on Penguin Bank is completed and time allows, the survey will be extended to other unmapped areas, such as near-shore areas around Molokai and Lanai.

To the extent feasible, multibeam depth data collected during the expedition will be processed aboard the Hi'ialakai with the goal of producing semi-final bathymetric maps and associated depth data ("gridded" data sets) while the cruise is in progress. After the cruise, as soon as basic data processing is completed, maps and gridded data sets will be supplied to government agencies responsible for managing Hawaii's marine ecosystems, including various offices of NOAA, the State of Hawaii, the U.S. Geological Survey, and the U.S. Fish and Wildlife Service.

Analysis of the data will proceed onshore over the coming months or years. In addition to bathymetry, the sonar data will be used to generate backscatter imagery which help reveal the nature and composition of the seafloor sediments and to produce derivative products such as slope and complexity maps. The bathymetric data will be integrated with other kinds of spatially-oriented data into a Geographic Information System (GIS) and used to produce benthic habitat maps to support marine resource research and management analysis. Seafloor maps generated from multibeam survey data will be available for use by research scientists assessing the distribution, abundance, and habitats of fishes, marine mammals, and other species in waters of the Hawaiian Archipelago.