Scientists use sophisticated sonar to map the seafloor in shallow habitats of the Northwestern Hawaiian Islands

October 8, 2006
image of AHI and Hi'ialakai
The 25-ft survey launch AHI approaches the 224-ft NOAA Ship Hi'ialakai. The vessels are being used to conduct sonar mapping of the seafloor in the Northwestern Hawaiian Islands.

A group of scientists from NOAA's Pacific Islands Fisheries Science Center, the Pacific Islands Benthic Habitat Mapping Center (PIBHMC), and the Joint Institute for Marine and Atmospheric Research (JIMAR), University of Hawaii, are using multibeam sonars and underwater cameras to describe bottom (benthic) habitat and associated marine life in the Northwestern Hawaiian Islands (NWHI). The research is being conducted by scientists on the NOAA Ship Hi'ialakai during October of 2006. The research expedition is funded by the NOAA Coral Reef Conservation Program as part of the program's mandate to produce comprehensive digital maps of all shallow (< 30 m deep) coral reef ecosystems in the United States and characterize priority moderate-depth reef systems by 2009.

Survey operations will be conducted at Brooks Bank and St. Rogatien Bank, and in waters surrounding Nihoa Island. The expedition is being led by Joyce Miller, a JIMAR researcher in PIFSC's Coral Reef Ecosystem Division (CRED).

Surveying will be conducted using two multibeam sonars aboard the Hi'ialakai and another multibeam unit installed on the R/V AHI, a 25-ft survey launch operated by CRED.

The multibeam mapping work is part of an ongoing mission to characterize the coral reef ecosystems of the Pacific. Since 2002, more than 41,000 km2 of bottom habitat have been mapped in the NWHI. All mapping data collected through calendar year 2005 are available for download at the PIBHMC Web site. Bathymetric data from the current cruise will be processed by mapping specialists and posted within a year of data collection. In addition to bathymetric data (data on depth of the seafloor), the sonar collects "backscatter data" that provide further information about the nature and composition of the seafloor; these data will also be made available via the Web site.

In addition to conducting the multibeam surveys, staff on the Hi'ialakai will deploy a baited bottom camera (called BotCam) as many as 60 times in waters between 50 and 300 m deep. BotCam was designed as a way to collect video images of marine life in the immediate vicinity of the camera and is being tested for a variety of potential applications. For example, BotCam may prove to be an effective way to collect data on bottomfish or other marine species without removing them from the ocean, thus providing a way to supplement conventional methods of fish population monitoring or an alternative data collection method to be used in situations where extractive sampling would be detrimental.

BotCam is deployed from the Hi'ialakai and retrieved by a small boat. After the camera reaches the bottom, a bait cloud is released into the water and a low light video camera records imagery of fish that are attracted to the bait and swim within range of the camera. A typical deployment involves several hours of video recording, after which researchers retrieve BotCam from the sea bottom. The video data are later analyzed to estimate the number and size of fish sampled. Data collected during the BotCam research will help scientists and managers determine whether the camera will be a useful tool for surveying and monitoring fish populations in waters of the NWHI and other Pacific Island marine habitats.