Effects of seismic air guns on marine fish

Abstract

Observations of marine fish and invertebrates on an inshore reef were made using TV and acoustic tags one week before, during, and four days after a seismic triple G. airgun (three synchronised airguns, each gun 2.5 l and 2000 psi) was deployed and repeatedly fired. The guns were fired once/min for eight periods on four days at different positions. The structure and intensity of the sound of each triple G. gun explosion was recorded and calibrated. Peak sound pressure levels of 210 dB (rel to 1 μPa) at 16 m range and 195 dB (rel to 1 μPa) at 109 m range were measured at positions where the fish were being observed. The final position of the triple G. gun, at 5.3 m range, had a peak pressure level of 218 dB (rel to 1 μPa). Neither the fish, nor the invertebrates, showed any signs of moving away from the reef. Firing the guns did not interrupt a diurnal rhythm of fish gathering at dusk and passing the TV camera position while the guns were firing. The long-term day-to-night movements of two tagged pollack were slightly changed by the arrival and banging of the guns particularly when positioned within 10 m of their normal living positions. Those reef fish, watched by the TV camera, always showed involuntary reactions in the form of a Mauthner cell reflex, C-start, at each explosion of the guns at all ranges tested (maximum range was 109 m, 195 dB rel to 1 μPa). When the explosion source was not visible to the fish, the C-start reaction was cut short and the fish continued with what they were doing before the stimulus. When the G. gun rack was sunk to the seabed (depth 14 m) visible to the fish and the TV camera, those fish that were observed approaching the G. gun rack when the guns were fired were seen to turn and flee from the very visible explosion. When the gun rack was suspended midwater (5 m depth) and just outside visible range at 16 metres, the fish receiving a 6 ms peak to peak, 206 dB (rel to 1 μPa) pressure swing exhibited a C-start and then continued to swim towards the gun position, their intended swimming track apparently unaltered. The sound of the G. guns had little effect on the day-to-day behaviour of the resident fish and invertebrates.