First Assessment of Effects of Air-Gun Seismic Shooting on Marine Resources in the Central Adriatic Sea

Abstract

Abstract A series of investigations were carried out to test the effects of air-gun seismic shooting on main fishery resources of the Adriatic Sea during summer 1995. The energy source used for the trial was formed by one air-gun array made up by two sub-arrays consisting in 8 air-guns each developing a total volume of c.a. 2500 i3 at 2000 psi with an amplitude of 60 bar/m. The interval between two was of 25 s The intensity was of 210 dB re 1 mPa-m/Hz. Acoustical and spectral analysis were performed simultaneously in the surveyed areas to correlate fishery and behavior observ ations with sound pattern of the energization. Main results were: Analysis of trawl catch data evidenced no significant changes before and after the air-gun seismic profiling.Echosurvey relative estimate of pelagic biomass, performed simultaneously to trawling operations, failed to evidence any significant change in the pelagic biomas.Small differences were observed in the trammel net catch composition, but one single set of pre-post fishing operations could be done in the study period.Similar density estimate were obtained from dredge surveys performed by an hydraulic dredger before and after air-gun seismic profiling over a clam bed in 14 md.Video recording of captive fish, kept into cages moored on the sea bottom at 12 m depth, evidenced a behavioral response to the approach of the sound source; but no lethal event was recorded on captive sea-bass immediately after the seismic shooting.Biochemical and histological analysis were performed to verify if it is to be related to the captive condition or is somewhat consequent to the air-gun energization. These results confirm that no relevant effects are induced on fishery resources by seismic air-gun shooting.