Observations of Sea Turtles and Other Marine Life at the Explosive Removal of Offshore Oil and Gas Structures in the Gulf of Mexico

Abstract

Observers monitored the explosive removal of oil and gas structures in the Gulf of Mexico to protect sea turtles and marine mammals from adverse impacts. More than 7,000 monitoring hours at 131 structure removals were conducted during 1993. Sixteen individual sea turtles were observed including 6 loggerheads, 1 Kemp's ridley, 1 green, and 8 unidentified sea turtles. Aerial surveys were approximately ten times more effective in observing sea turtles than day or night surface surveys. INTRODUCTION During the summer of 1993 oil and gas production platforms in the Gulf of Mexico totaled nearly 4,000. This number did not include hundreds of smaller, non-producing structures such as well jackets and caissons. Nearly al l of these are located in waters off the Louisiana and Texas coasts. Owners are required by federal regulations to remove these structures within one year after lease terminati0n.I The most economical removalmethodutilizes underwater explosives which can have a negative impact on local marine life. During the past four years, explosive structure removals averaged more than 120 annually. Sea turtles are known to frequent reefs and other areas with submerged structures (Stoneburner 1982; Carr 1954; Booth andPeters 1972; Witzelll982). Consequently, it is not surprising to find sea turtles at oil and gas structures (Gitschlag and Renaud 1989; Gitschlag and Herczeg 1994; Gitschlag and Hale') which are themselves artificial reefs. Although al l five species of sea turtles inhabiting the western Gulf of Mexico are listed as either threatened or endangered, attention to the ef€ects of platform salvage did not occur until 1986. In the spring of that year, 51 sea turtles and 41 bottlenose dolphin (Tursiops truncutus) washed up dead on north Texas beaches coincidental with the explosive removal of structures just a few miles offshore (Klima et al1988). This resulted in a formal consultation authorized under the Endangered Species Act between the National Marine Fisheries Service (NMFS) and Minerals Management Service ( M M S ) , the agencieswith jurisdiction in federal waters. One consequence of the consultation was a procedure requiring oil and gas companies to obtain a permit from M M S prior to using explosives in federal waters. An Incidental Take Statement accompanying the formal consultation prepared by NMFS was included in the permit and described requirements to protect sea turtles (Table 1). Among these requirements was the use of personnel trained to monitor for sea turtles. Similar procedures were established for structure removals in state waters where permits were obtained from the U.S. Army Corps of Engineers (COE). Mandatory use of trained observers began in 1987. This article Summarizes the 1993 findings of the NMFS monitoring program at explosive structure removals in the Gulf of Mexico plus two additional platforms which were originally scheduled for explosives but were actually removed using mechanical techniques. MATERIALS AND METHODS Surveys were conducted from helicopters (aerial surveys) as well as from vessels and oil and gas platforms ( d a c e surveys). The area within a 1600 m radius of the removal site was monitored during 30 min preand postdetonation aerial surveys at altitudes of 150-200 m, speeds of 100-150 kph, and only during daylight hours. Surface surveys usually began at least 48 hours prior to detonation of explosives and were typically conducted from a vessel positioned immediately adjacent to the structure being salvaged. Surface surveys were occasionally performed at Oil, Gas and Sulfur Operations in the Outer Continental Shelf, 30 CFR (250 series). 2Gitschlag, G.R and J.K. Hale. Susceptibility of Sea turtles to underwater explosives at offshore energy structure removals. Unpubl. manuscr. on file at NMFS Galveston Laboratory, SEFSC, Galveston, TX 77551. 247