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 the Pacific Reef Assessment and Monitoring Program (RAMP) Cruises. 11 towboard surveys (17.39 km in length), were conducted at Howland during the Pacific Remote Island Areas RAMP Cruise HA1201 from 20120227 to 20120325. 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., Crown of Thorns sea stars, 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 15 m. 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 (greater than 50 cm total length) seen within 5 m either side and 10 m 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 5-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 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 are approximately 200 pictures for 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-letter abbreviation of the island or bank surveyed, MMDDYY is the local date of the towboard survey, X is the Xth dive on the day, and ### is the sequence number of the pictures taken for that particular dive. As an example, JAR032106_3_108.JPG means the picture was the 108th picture taken on 3rd dive of March 21, 2006 at Jarvis Island.
Ground Condition
Please cite CRED when using data. Coral Reef Ecosystem Division (CRED), Pacific Islands Fisheries Science Center (PIFSC), National Marine Fisheries Service (NMFS), National Oceanic and Atmospheric Administration (NOAA)
NOAA IRC
NMFS/PIFSC/CRED
1845 WASP Blvd., Building 176
e-mail preferred
Jacob Asher, Coral Reef Ecosystem Division (CRED); Marie Ferguson, Coral Reef Ecosystem Division (CRED)
Observations were made by divers who are expert 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 or bank surveyed.
The towboard surveys are completed in forereef, backreef, and lagoon habitats. The minimum spatial resolution of the towboard survey is the 5-minute survey segment which covers approximately 200 m. As such, these surveys are appropriate for broad estimates but can not be used for fine scale, site-level data analysis.
Although resource grade GPS units were used and a layback model was applied to the survey tracks, the exact survey positions were not physically marked and effort was not made to re-visit exact same tracks.
Instrument parameters
SeaBird SBE-39 temp/depth recorder
The towboard survey involves a pair of scuba divers who are towed 60 m behind a small boat at a constant speed (~1.5 knots). 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 ten 5-min segments. During the survey, the fish diver records, to the lowest possible taxon, large fishes observed within a survey swath 5 m to either side of the diver and 10 m in front the diver.
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
