Top Main Section

Top Main Component


Marine Mammals Observer and Passive Acoustic Monitoring

Εxperienced Marine Mammal Observers (MMOs) and Passive Acoustic Monitoring (PAM) Operators were on board the seismic vessel whose primary role was to detect marine mammals and to advise on stopping of the air guns upon detection of marine mammals within the exclusion zone and initiate soft start to give marine mammals enough time to move away from the acoustic source and outside the exclusion zone.

Two expert MMOs (daylight hours) and two dedicated PAM Operators (24-hours) worked onboard the seismic vessel throughout the entire 3D and 2D MSS acquisition activities. Visual monitoring and Passive Acoustic Monitoring were carried out prior to commencement and throughout acquisition activities. The MMO’s conducted visual watches for marine mammals during daylight hours, from sunrise to sunset. Passive Acoustic Monitoring for marine mammals was carried out throughout the entire day to ensure optimal detection probability. Passive acoustic daily monitoring along with Marine Mammal observation were logged and recorded accordingly.

There were six sightings of at least one species, with a total estimate of 16 individuals. No sightings resulted in a start-up delay, but one sighting resulted in a shut-down of a soft-start. Five out of six sightings were observed by MMOs whilst on effort, and one was observed by vessel crew aboard the workboat. All visual sightings recorded throughout the survey are shown in the following table:

Acoustic Monitoring

The Patraikos Gulf Acoustic Monitoring Project was an ongoing project for measuring the acoustic levels before, during and after the 3D Marine Seismic Survey carried out by HELPE S.A. Sensitive zones and exclusion zones of normal operation of airguns were designated within the project area. Those zones included sensitive environmental elements, which were proposed to be included in the monitoring plan. The proposed monitoring carried out by means of survey, allowing for:

  • verify the actual presence of mammals
  • define the background noise level and verify the anticipated Exclusion Zone

A research vessel was used to carry out the acoustic survey and two separate portable systems were used for the monitoring of the ambient noise on the four predefined stations.

Ambient noise measurements (prestart and post completion of seismic activities) at the proximity of the four (4) predefined locations

The objectives of this acoustic study was to measure ambient sound levels as a function of sound frequency components, time and position as well as correlate acoustic anomalies to major acoustic sources within the survey areas:

a. Prestart

In general, all stations exhibited high ambient sound levels concentrated on the top (or above) limit of the bibliographic prevailing ambient noise. This was partially due to the sampling procedure, which involved:

  • Shallow deployment (in just 20m water depth) and close to the shore. The above induced high levels of benthos, sea surface bubble and spray and offshore turbulence fluctuations noises, and
  • Deployment in proximity to sea-farms which in some cases induced high levels of mechanical noise caused by the specific “industrial” (mechanical) activity.

b. Post Completion

A main conclusion of the report was that no significant differences have been observed in the ambient noise between the pre-start and the post completion stages of the 3D seismic survey, implying that no seismic noise has remained in the soundscapes of the monitored areas. Small ambient noise differences in both the frequency and spatial domains may occur due to: (1) slightly different sampling locations (different depth ranges and proximities to the coasts as the vessel was drifted by the currents and the wind), (2) different traffic noise loads and (3) other random noises (weather conditions, self-noises etc.).

Seismic noise monitoring & Verification of Exclusion Zone

The aim of the acoustic survey at that stage was to assess the sound pressure level of the noise induced by the air-gun seismic source to the predefined sampling locations. During the seismic noise monitoring, a total of 30 deployments have been realized. Additionally, field measurement of noise levels around the seismic source (air-guns) were carried out during the acquisition activities in order to record and study the seismic noise attenuation levels and validate the specified mitigation zone. None of the measured values exceeded the threshold values defined for permanent loss (PTS) and temporary loss (TTS) of auditory sensitivity for marine mammals (Southall et al., 2007) at any distance.

Coastal Zone Inspection for the Presence of Marine Mammals

A visual inspection for marine mammals’ presence was carried out. The vessel departed from Astakos port heading to the survey area. A coastline of 35 nm was visual inspected and twenty predefined areas were closely approached. The areas with the highest likelihood of marine mammal presence were selected based on the coastal morphology and sea currents directivity. The visual inspection of the coastal zone environment did not show any mammal.