Effects of seismic air guns on marine fish

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 s eismic triple G. airgun (three synchronised airguns, each gun 2.51 and 2000 psi) was deployed and repeatedly fired. The guns were fired once/min for e ight periods on four days at different positions. The structure and intensi ty of the sound of each triple G. gun explosion was recorded and calibrated , Peak sound pressure levels of 210 dB (rel to 1 mu Pa) at 16 m range and 1 95 dB (rel to 1 mu Pa) at 109m range were measured at positions where the f ish 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 mu Pa). Neither the fi sh, nor the invertebrates, showed any signs of moving away from the reef. F iring 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 longter m 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 o f 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 mu Pa). When the explosion source was not visib le to the fish, the C-start reaction was cut short and the fish continued w ith what they were doing before the stimulus. When the G. gun rack was sunk to the seabed (depth 14m) visible to the fish and the TV camera, those fis h that were observed approaching the G. gun rack when the guns were fired w ere seen to turn and flee from the very visible explosion. When the gun rac k was suspended midwater (5 In depth) and just outside visible range at 16 metres, the fish receiving a 6 ms peak to peak, 206dB (rel to 1 mu Pa) pres sure swing exhibited a C-start and then continued to swim towards the gun p osition, their intended swimming track apparently unaltered. The sound of t he G. guns had little effect on the day-to-day behaviour of the resident fi sh and invertebrates. Crown Copyright (C) 2001 Published by Elsevier Scienc e Ltd. ALI rights reserved.