Seismic surveys are used to produce detailed images of local geology to determine the location and size of possible oil reservoirs (Richardson et al., 2017). Marine seismic surveys are normally carried out using sound sources consisting of arrays of airguns. Airguns are device that produce sound by suddenly releasing high-pressure air into the water. The resulting acoustic signal is made up of a short, high amplitude pulse followed by a decaying series of lower amplitude pulses (Duncan et al., 2017). The released sound is attenuated and reflected at geological boundaries. The reflected signals are detected then processed to provide information about the structure and composition of geological formations below the seabed to identify hydrocarbon reservoirs (Richardson et al., 2017).
Seismic surveys can have adverse side effects on marine life. Experimental air gun signal exposure was found to decrease zooplankton abundance when compared to controls. Mortality rate after exposure to seismic waves increased from a natural rate of 19% per day to 45% per day. Impacts were observed out to the maximum 1.2km range sampled (McCauley et al., 2016). Zooplankton underpin the health and productivity of global marine ecosystems. Consequently, mass zooplankton mortality due seismic survey exposure could have significant negative implications for ocean ecosystem function and productivity. The Great Australian Bight has abundant levels of zooplankton and is classified as a sardine driven ecosystem. A decrease in the abundance of zooplankton has the potential to have flow-on implications across the wider ecosystem of the Great Australian Bight.
Impacts of noise from seismic surveys are of concern to marine environments because sound travels faster, further and with more energy in water than in air. Marine animals have well-developed auditory systems that are used in social interactions, foraging, orientation and in predator avoidance (Richardson et al., 2017). Sound from seismic surveys can interfere with these functions by altering physiology, behaviour and masking of communication and auditory cues (Southall et al., 2007).
Historically there have been a number of small scale, short term 2D seismic surveys utilising small airguns or other detonation devices in the region. However, it was the first large scale long-term 3D survey in the ultra-deep area of the GAB operating from November 2011 to June 2012 that really alerted us to the detrimental effect these surveys can impart on SBT migration and behaviour.
Duncan, A. J., Weilgart, L. S., Leaper, R., Jasny, M., Livermore, S., (2017). A modelling comparison between received sound levels produced by a marine Virboseis array and those from an airgun array for some typical seismic survey scenarios. Marine Pollution Bulletin. Doi: 10.1016.
McCauley, R.D., Day, R.D., Swadling, K. M., Fitzgibbon, Q. P., Watson, R. A., Semmens, J. M., (2016). Widely used marine seismic survey air gun operations negatively impact zooplankton. Nature Ecology and Evolution: 1, 0195
Richardson, A. J., Matear, R. J., Lenton, A., (2017). Potential impacts on zooplankton of seismic surveys. CSIRO, Australia. 34 pp.
Southall, B. L., Bowles, A. E., Ellison, W. T., Finneran, J. J., Gentry, R. L., Greene, C. R., Kastak, D., Ketten, D. R., Miller, J. H., Nachtigall, P. E., Richardson, J., Thomas, J. A., Tyack, P. L., (2007). Marine Mammal Noise Exposure Criteria: Initial Scientific Recommendations. Aquatic Mammals: 33, 0167-5427.