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

La Bella, G. (Agip S.p.A.) | Cannata, S. (Centro Oceanologico Mediterraneo S.C.p.A.) | Froglia, C. (CNR - I.R.Pe.M.) | Modica, A. (Centro Oceanologico Mediterraneo S.C.p.A.) | Ratti, S. (Agip S.p.A.) | Rivas, G. (Centro Oceanologico Mediterraneo S.C.p.A.)

OnePetro 

G. La Bella, AGIP S.p.A., S. Cannata, Centro Oceanologico Mediterraneo S.C.p.A., C. Froglia, CNR - I.R.Pe.M., A. Modica, Centro Oceanologico Mediterraneo S.C.p.A., S. Ratti, AGIP S.p.A., and G. Rivas, Centro Oceanologico Mediterraneo S.C.p.A.

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 observations with sound pattern of the energization.

Main results were:

1) Analysis of trawl catch data evidenced no significant changes before and after the air-gun seismic profiling.

2) Echosurvey relative estimate of pelagic biomass, performed simultaneously to trawling operations, failed to evidence any significant change in the pelagic biomass subsequent to the seismic shooting.

3) 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.

4) 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 m depth.

5) 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.

6) 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.

Introduction

The Adriatic sea in contrast to the other parts of the Mediterranean basin is characterized by relatively wide continental shelf. Moreover it receives nearly 1/3 of the total Mediterranean river run-off, with its load of nutrients and pollutants. These features and local oceanography induce a rather high primary production sustaining important fishery resource, The Adriatic fishery industry lands about half of total Italian seafood production. Fishery exploits demersal resources over trawlable grounds, small pelagic fish (Clupeoids) and bivalve mollusks.

Most of the Italian fishing fleet is engaged in bottom trawling. The high prices paid by consumers for fresh local fish compensate for the recent decline in landings of some species, probably over-exploited.

Small pelagic fish (Anchovy and Sardine) is fished for human consumption by 200 medium size vessels (50-150 GRT). Annual production has wide fluctuations and in the last years ranged between 40,000 and 110,000 tons.

Venerid clams, which annual landings dropped to 60,000 tons from the over 100.000 tons recorded in the early '80s, are exploited by a fleet of 800 high-technology hydraulic clam dredger.

The value of the Adriatic catch is estimated in 9 billion US$/year, and fishery has a relevant importance for coastal populations of the area.

Interest of oil companies for the Adriatic basin, as a potential source of natural gas and/or oil rapidly increased after World War II. Interference of minerary operations with fishery activities is a world-wide problem and the Adriatic area makes no exception.

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