Introduction

         The benthic habitat of the continental shelf is not a homogeneous region of mud habitat, but also contains natural sand banks. As local sand resources are depleted, requests are being made for the use of identified Minerals Management Service Outer Continental Shelf (MMS-OCS) sand resources for coastal restoration activities. Natural sand banks represent an exploitable sand resource for beach renourishment and stabilization. Some of the raised sediment banks under consideration may provide a distinctive habitat. The relief of these banks may serve as a special habitat resulting in benthic community differences between areas on the bank, in the surrounding areas, and in the ecotone between the bank and surrounding areas. Bank habitat may be of particular importance as nursery habitat for juvenile fishes including red snapper, Lutjanus campechanus Poey, a commercially important species (Szedlmayer and Howe, 1997). MMS Sand and Gravel has in turn initiated scientific studies to examine the potential impacts of sand mining on the biological communities of offshore borrow areas.
 

Background

         Extensive beach restoration projects along the Gulf Coast of the United States are placing increased pressure on the known offshore sand resources, within state waters. The region has experienced serious erosion, subsidence, and loss of coastal shorelines. Most usable sand deposits, for coastal and beach restoration, occur within the submerged offshore shoals, on the inner continental shelf. However, such areas may be important ecologically and economically, representing essential fish habitat (EFH) for exploited resource fish species. The relief of these banks may provide a special microhabitat with a different benthic community residing within on-bank, off-bank, and ecotone areas based upon a combination of sediment grain size and energy regime (Neuman & Able 1998, Wright et al. 2000, Bergen et al. 2001). Many coastal fish species settle out on sand banks as juveniles and exploit the shoal areas for both habitat and feeding purposes. Juvenile fishes are less mobile and can be habitat specific such that small changes (i.e., the presence of biogenic structure) may make the difference between the habitat being unacceptable versus essential. Small changes in habitat quality that affect either the growth and/or survival of juveniles may also have a large impact on fish population size (Diaz et al. 2003). The potential for long-term adverse impacts to organisms both demersal fishes and invertebrates, as a result of offshore dredging, may occur if the physiography of a shoal feature is altered significantly. Little information is available relative to the habitat these offshore shoal areas provide for fish species. Before sand resources are exploited, detailed and specific information on biological communities and habitat relationships of organisms is needed.  This information is vital if adverse impacts to fish species that inhabit the shoal regions are to be avoided or mitigated in the future.

         Fish assemblages will be quantitatively evaluated in potential sand resource areas in the northwestern Gulf of Mexico to assess the relationships among sediment types and the spatial distribution of communities. This geo-referenced information will be used to assess the potential for disturbance to biotic communities from sand mining.
 

Goal

         The goal of this project is to provide a quantitative community assessment for benthic habitats in shallow shelf environments of the northwestern Gulf of Mexico, with emphasis on Sabine Bank, a potential source of sand resources.
 

Cruise Objectives

         As part of the USGS investigation, Texas A&M University has been contracted to provide detailed maps of bottom sediment types based upon the interpretation of ground-truthed, side-scan sonar backscatter data. The contract also requires a CHIRP seismic sub-bottom profiling, to provide information on sediment facies, and to facilitate sediment characterization and classification.  Additionally, single-beam depth surveys will be conducted during the side-scan transects to provide high resolution bathymetry information. The first of two data gathering cruises for this work was conducted on October 6-9^th, 2003. The resulting data has not been analyzed yet and another data collection cruise has been scheduled for late December, 2003, to January, 2004. Once this data is processed, it will be used by the USGS on future sampling cruises, and will improve the precision and accuracy of the assessment of discrete sediment-based habitats on the potential sand resource area of Sabine Bank.

         The objectives of the USGS July, 2003, sampling/gear testing cruise were:

• Reconnaissance fish sampling to ground truth our sampling methodology, including the documentation of a resident species list.
   
• Quantitative assessment of any dominant demersal fish community (including juvenile  red snapper) differences between the Sabine Bank habitat versus adjacent deeper waters.
   
• Comparative quantitative assessment of any dominant demersal fish community (including juvenile red snapper) differences between the center versus edge habitat of Sabine Bank.
   
• Testing of effective trawl collection on sand bank habitat including examining such factors as trawl specification (i.e., tickler chain vs. cookies), speed, and duration.
   
• Testing of effective sediment collection using a modified box grab.
   
• Testing of effective water parameter monitoring using a SEABIRD SBE-19Plus self -recording Conductivity, Temperature, and Depth profiler (CTD), including testing of the protective cage.
   
• Testing of the efficiency and logistics of using GPS navigational equipment attached to the trawl itself to record its track in coordination with onboard navigational software (GeoTracker).

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