Master of Science (MS)
Oceanography and Coastal Sciences
With over ~2600 oil and gas platforms (platforms) remaining in the northern Gulf of Mexico (Gulf), the Gulf States have access to one of the most unique fisheries in the world. Because of high abundances of game fishes around platform legs and the popular belief that platforms enhance fish stocks, both Louisiana and Texas have created artificial reef programs based upon the decommissioning of platforms. As oil and gas fields continue to be retired, oil and gas companies may find that “reefing” or toppling a platform may be a more economically viable alternative to complete removal of material. Questions remain about how platforms should be decommissioned and whether the moved material affects fish density by changing habitat complexity. In this study, I define habitat complexity as a change in one or all of three variables: vertical relief, footprint and volume of the structure. The objective of this study was to show which of these variables has the greatest effect on changes in fish density with depth in the water column and distance from the site. Mobile hydroacoustic surveys were taken over a period of four years, yielding target strength (TS) (dB) values and mean volume backscattering strength (MVBS) values that could be converted into fish per cubic meter, or fish density. Upon reefing, fish density at the site increased. There was no significant change in density with distance from the site but depth proved to be an important factor. Overall density increased after reefing, with the most substantial increase shown in between 40-60 m depth within the water column, the layer that contained most of the platform material after reefing. The reefed site decreased in vertical relief but increased in footprint and volume. A regression tree revealed that volume was the variable responsible for the greatest variability among densities. Even though there was a much greater percent change in overall footprint compared to volume after reefing (1,024% increase in footprint versus 55% increase in volume) volumes are 3 dimensional (m3 vs. m2) and the platforms permeable, allowing fish to seek refuge within the site.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Harwell, Grace Elizabeth, "Acoustic biomass of fish associated with an oil and gas platform before, during, and after "reefing" it in the northern Gulf of Mexico" (2013). LSU Master's Theses. 2912.
James H. Cowan Jr.