Title:
CRED Towed-Diver Fish Biomass Survey at Tutuila, American
Samoa in 2012
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. 6 towboard surveys (totaling 13.51
km in length) were conducted from 20120227 to 20120325 and another 27 towboard surveys (totaling 58.72
km in length) were conducted at Tutuila in American Samoa
from 20120401 to 20120426 as part of RAMP Cruise HA1201.
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.