The response of marine finfish and invertebrates to seismic survey noise

Abstract

The oil and gas industry is of major economic importance to Australia. Offshore seismic surveys are an essential component of exploration for fossil fuel reserves. Offshore seismic surveys involve the use of arrays of air-guns that produce repetitive high energy, low frequency sound. There is increasing concern about the effect that the noise generated by a seismic survey has on the surrounding marine life. Various species of captive marine fish and one species of squid were exposed to the noise from a single Bolt PAR 600 B air-gun with a 20 cui firing chamber and a source level at 1 m of 203.6 dB re 1 μPa mean squared pressure. Ten trials were conducted in Jervoise Bay and two were carried out off the coast of Exmouth. A different noise regime was used in each trial, however most involved the use of approach-depart scenarios to simulate an actual seismic survey and a 10 second duty cycle. Noise levels received by the animals ranged between 128 - 192 dB re 1 μPa mean squared pressure. Behavioural observations of the fish and squid were made before, during and after air-gun noise exposure. The physiological stress response of the fish was monitored by measuring plasma cortisol and glucose levels before and after noise exposure. The sensory epithelium was removed from the ears of the fish prior to, immediately after and up to 86 days after air-gun noise exposure and examined using a scanning electron microscope. No statistically significant physiological stress response in fish was detected as a result of the air-gun noise exposure regimes used. Significant damage to the ciliary bundles of the sensory epithelium of the sacculus was observed in pink snapper (Pugrus auratus) that had been exposed to air-gun noise between 144 - 191 dB re 1 μPa for 1.71 hours. No regeneration of the hair bundles was observed 58 days after exposure to air-gun noise.However, evidence of regeneration was observed between 58 and 86 days after noise exposure. Behavioural observations suggested that as air-gun noise levels increase, fish respond by swimming faster, in tighter groups and towards the bottom of the water column. Significant increases in alarm responses were observed in fish and squid to air-gun noise exceeding 158 - 163 dB re 1μPa. An increasing proportion of alarm responses were also observed as the noise level increased. A decrease in the frequency of alarm responses for repeated exposures was observed in squid and some fish. The implications of these findings are discussed with comparisons of noise levels measured from an actual 2678 cui seismic survey air-gun array.