To support NOAA Coral Reef Conservation Program (CRCP) long-term goals for sustainable management and conservation of coral reef ecosystems, towed-diver surveys (aka. towboard surveys) were conducted by the Coral Reef Ecosystem Division (CRED) of the NOAA Pacific Islands Fisheries Science Center (PIFSC) as part of biennial Pacific Reef Assessment and Monitoring Program (RAMP) Cruises. 16 towboard surveys (36.8895 km in length), were conducted at Tutuila Island during the American Samoa RAMP Cruise TC0201LegII from 9 February - 3 March 2002. Towboard surveys are a good method for obtaining a general description of large reef areas, assessing the status of low-density populations of large-bodied reef fish, large-scale disturbances (e.g., bleaching), general distribution and abundance patterns of macro-invertebrates (e.g., COT, giant clams), and for assessing trends in these populations and metrics. A pair of scuba divers (1 fish and 1 benthic diver) are towed 60 m behind a small survey launch at a speed of 1-2 knots and a depth of approximately 15m. Each survey is 50 min long, covers about 2 km of habitat, and is divided into ten 5-minute survey segments. The fish diver records, to the lowest possible taxon, all large-bodied reef fishes (>50cmTL) seen within 5m either side and 10m in front of the towboard. Length of each individual is estimated to the nearest cm. The fish towboard is also outfitted with a forward-facing digital video camera to record the survey swath. The benthic diver records percent cover of coral and macroalgae, estimates benthic habitat type and complexity, and censuses a suite of benthic macroinvertebrates including Crown of Thorns sea stars and sea urchins. The benthic towboard is equipped with a downward-facing digital still camera which images the benthos at 15 second intervals. These images are analyzed for percent cover of coral, algae, and other benthic components. Both towboards are equipped with SEABIRD SBE-39 temperature/depth sensors set to record at 5 second intervals. Latitude and longitude of each survey track is recorded at 15 second intervals using a Global Positioning System (GPS) receiver onboard the tow boat. A layback algorithm is applied to more accurately map the position of the divers with respect to the reef environment. This algorithm calculates the position of the divers based on the position of the tow boat taking into account the length of the tow rope, the depth of the divers, and the curvature of the survey track. This metadata applies to the benthic characterization observations.
Part of a long-term monitoring program at biennial intervals which documents the state of the reefs.
The benthic characterization observation data includes benthic composition, complexity estimations, observed macro-invertebrates, and observed man-made objects. Classification of habitat complexity was recorded in six categories: low (L), medium-low (ML), medium (M), medium-high (MH), high (H), and very high (VH). Benthic cover was estimated for four different types of substrate: hard substrate/pavement, sand, rubble, and live hard (scleractinian) coral. The time of the benthic digital photos were set to the GMT time. There were approximately 200 pictures of each 50-minute towed survey track. The resolution at "Draft" quality (the lowest) is 72 pixels/inch. The resolution at "Best" quality (the highest) is 266 pixels/inch. The naming convention of benthic photos is ***MMDDYY_X_###.JPG, where *** is 3 letters abbreviation of island/bank surveyed, MMDDYY is the local date of towboard survey, X is the Xth dive on the day of MMDDYY, and ### is the sequence number of the pictures taken at the Xth dive. For example, JAR032106_3_108.JPG means the picture was the 108th picture taken at 3rd dive on March 21, 2006 at Jarvis Island.
Ground condition
Please cite CRED when using the data. Coral Reef Ecosystem Division, Pacific Islands Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration
NOAA IRC
NMFS/PIFSC/CRED
1845 WASP Blvd., Building 176
e-mail preferred
, Coral Reef Ecosystem Division (CRED), Pacific Islands Fisheries Sciences Center, National Marine Fisheries Service, NOAA
Observations were made by the divers who are experts in coral reef ecologist. Surveying in this habitat will greatly depend on the current, wave conditions and field scheduling. The towed-diver survey is conducted one time per site per survey year; it is not replicated. Divers may change from year to year and by location.
The same data collection protocols were used at each island/bank surveyed.
The towed-diver surveys are completed in forereef, backreef, and lagoon habitats. Considering that the towed-divers are covering ~200 m during each 5-min time frame of a 50-minute survey, benthic coverage calculations are broad estimates. These data can be used to see large differences but can not be process to a fine scale.
Although resource grade GPS units were used and a layback model was applied to the survey tracks, the exact survey positions were rarely marked and little effort was made to revisit exact same tracks.
Instrument parameters
Dive computer and SCUBA depth gauge
Benthic towed-diver surveys involve a SCUBA diver who maintains approximately 1 meter above the bottom and is towed 60 m behind a boat at a constant speed (~1.5 knots). The diver maneuvers a towboard equipped with a downward facing still camera that is programmed to take photographs of the benthos at every 15 seconds as well as a SBE39 depth/temperature recorder which records the temperature and depth every 5 seconds. The towboard survey is typically 50 min long and covers about 2 km of habitat, depending on the depth profile of the divers. The survey is divided into 5 min segments. During the survey, the benthic diver records benthic composition, complexity estimations, observed macro-invertebrates, and observed man-made objects.
While every effort has been made to ensure that these data are accurate and reliable within the limits of the current state of the art, NOAA cannot assume liability for any damages caused by errors or omissions in the data, nor as a result of the failure of the data to function on a particular system. NOAA makes no warranty, expressed or implied, nor does the fact of distribution constitute such a warranty.
Contact CRED data management team for information
