Impacts of the explosive removal of offshore petroleum platforms on sea turtles and dolphins

Abstract

Strandings of 51 dead sea turtles (primarily Kemp's ridley, Lepidochelys kempi), 40 dolphins (primarily bottlenose dolphin, Tursiops truncatus) and many fish were recorded on beaches in the northwestern Gulf of Mexico from 19 March to 19 April 1986. During this period explosives were used to remove several oil platforms in adjacent offshore waters. Drift bottles released at the site of one of the explosions were recovered with some of the strandings. Shrimp fishing activity, a known cause of turtle mortality, was at a normal seasonal low. Circumstantial evidence suggests that at least some of the strandings of marine animals may have been due to underwater explosions used in removal of oil platforms. A total of 11 turtles were observed at 7 of 52 removal sites from 5 April 1986 through 5 August 1988, and a maximum of 100 dolphins were observed at each of 38 sites. One wild sea turtle was observed sinking after an explosion, but it could not be recovered to document its injuries. Necropsy of one stranded loggerhead turtle, Caretta caretta, found two days after a 1987 removal showed hemorrhaging of the lungs which is consistent with impacts of an explosion; this condition may also be attributed to postmortem decomposition of tissue. In a preliminary experiment, two of four Kemp's ridley and three or four loggerhead turtles were rendered'imconscious after placement within 915 m of the simultaneous explosion of four 23 kg charges. Comparison of turtle strandings during periods characterized by high and low numbers of offshore explosions, March-April 1985–88, suggested a positive relationship between the frequency of explosions and the stranding of turtles. Although dolphins may be impacted by explosions, the relationship between the stranding of dolphins and offshore explosions was not as conspicuous.