Title:
CRED Towed-Diver Fish Biomass Survey at Ofu & Olosega,
American Samoa in 2010
Abstract:
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) are
conducted by the Coral Reef Ecosystem Division (CRED) of the
NOAA Pacific Islands Fisheries Science Center (PIFSC) as part of
Pacific Reef Assessment and Monitoring Program (RAMP) Cruises.
14 towboard surveys (totaling 29.23 km in length) were conducted
at Ofu & Olosega in American Samoa from 2010-02-17 to
2010-03-23 as part of RAMP Cruise HA1001. 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 diver 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 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 fish
biomass observations.
Supplemental_Information:
Data collected: Species level abundance and length information
for coral reef fishes greater than 50 cm total length. Data is
linked to a geographic shapefile via DiveID or SegID. Abundance
and/or biomass data can be provided at the species or family
level.