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Introduction
This is the final report of our CMP Cycle 11 project to identify and delineate oyster reefs
and other bottom features in Copano Bay. This project is being conducted during two
successive CMP Cycles, Cycles 11 & 12. During the Cycle 11 we conducted the bulk of
the field component of the geophysical mapping. Cycle 12 will be used to process the
geophysical data and generate maps and prepare the final report. This project is a
cooperative effort between Department of Oceanography, Texas A&M University
(TAMU), Department of Marine Sciences Texas A&M University at Galveston
(TAMUG), the Institute for Coastal Studies at Texas A&M University at Corpus Christi
(TAMUCC), and the Texas Parks and Wildlife Department (TPWD).
Study Site
Copano Bay is a shallow (2-3 m), microtidal estuary in south central Texas (Figures 1 and
2). It is approximately 8 to 10 km wide and up to 26 km long with an area of about
69.5mi
2
(Calnan,1980). It is a secondary bay to Aransas Bay with three main rivers that
provide freshwater and sediment inflow to the estuary.
Work Conducted
Geophysical data were collected aboard the R/V Sammy Ray (Figure 2) over an eight week
period from June 2007 through July 2007 along the survey lines shown in Figure 2. Copano
Bay was surveyed using sidescan sonar, CHIRP sub bottom sonar and single beam
bathymetry. Grab sediment samples were also collected to correlate sidescan backscatter
intensity.
Sidescan Sonar
The sidescan sonar survey was conducted using an Edgetech® 272TD sidescan sonar
towfish operating at 100 kHz. Survey line spacing was 150m with a swath width of
100m to provide maximum coverage of the seafloor. Due to the shallow water depths of the
Bay the towfish was attached on a PVC catamaran along the starboard side of the research
vessel (Figure 4).
Data were acquired digitally using CodaOctopus® Geosurvey software that combines
sonar images with navigation data supplied by a Trimble®DGPS receiver. The data was
then mosaicked and exported as a georeferenced image (Figure 5).
The high-frequency acoustic signal of the sidescan allows surficial sediments to be mapped
based on backscatter intensity. Higher backscatter areas consisting of hard substrates, such
as oyster reefs, are depicted as lighter areas on the produced image, while low backscatter
soft substrate areas, such as silts and clays, appear as darker areas.
Bathymetry
Single-beam bathymetry was collected using an Odom Hydrotrac operating at a 200 kHz
frequency and Hypack® software. Tide corrections were made to the data in Hypack®
using the NOAA tidal station (ID #87745 13) located at the main opening of Copano Bay