One blast from airguns and echo sounders in operation.
Source: NOAA Pacific Marine Environmental Laboratory VENTS Program.
This sound is from a 48 air-gun array towed behind an oil & gas prospecting seismic survey vessel, detonating with a force powerful enough to penetrate 40 kilometers deep into the earth’s crust below the sea floor to detect oil reserves. These bursts of pressure sound waves are generated every 10 seconds, 24 hours a day and can continue for 6 months at a time. This high intensity sound reaches 230dB or more, roughly comparable to a sound of a space shuttle launch. To give context, in South Africa, the labour law does not allow employees to work in noise levels over more than 85dBA (150dBA equivalent in water).
EFFECTS TO MARINE LIFE
An enormous amount of marine life relies on sound for survival. They use it for social bonding, finding mates, aggression, finding prey, avoiding predators and navigation.
It has been shown that these survey sounds can be heard underwater thousands of kilometres from the survey ship. Needless to say these surveys have some devastating impacts to marine life including soft tissue damage, hearing loss, the bends, disorientation, displacement, migratory diversion and animal stranding.
Here is just some of the latest research:
- A study commissioned by the Namibian government revealed that an 84% decline in tuna catches (650 tonnes in 2013 from 4,046 tonnes in 2011) was a result of an increase in seismic exploration for oil and gas in the Orange River Basin driving tuna from their normal migratory routes.
- McCauley, Fewtrell and Popper (2003) found that the ears of fish exposed to an operating airgun sustained extensive damage to their auditory hair cells (sendory epithelia). The damage was severe, with no hair cell regeneration 58 days after air-gun exposure. This damage was seen at exposure levels that might occur several kilometers away from the airguns.
- Airgun operations kill large swathes of plankton, the basis of the marine food chain, up to 1.2km from the sound source. Within the study area, zooplankton abundance dropped by two-thirds. Furthermore, all larval krill, the primary food source of whales, were killed (McCauley et, 2017). The current seismic survey covers nearly 240 000 km2 in a current moving on average at 5kms an hour creating a massive destruction of zooplankton. McCauley et al warn of the ramifications for ocean ecosystem structure and health considering a significant component of zooplankton communities comprises the larval stages of many commercial fisheries species and healthy populations of fish, top predators and marine mammals are not possible without viable planktonic productivity.
- The assumption that received airgun noise levels decrease with less and less impact on the exposed animals further from the noise source was overturned by Madsen et al (2006). They found high exposure levels at considerable ranges from the air-gun array and that received sound pressures and sound exposure levels may actually increase with range beyond 5 km range up to 12.6 km from source. They believe this high frequency acoustic by-product on marine mammals should not be dismissed lightly and that it poses the challenge of how to mitigate where animals can dive in and out of high exposure levels at considerable ranges from the air-gun array.
- Mann et al (2010) claim that hearing impairment could play a significant role in some cetacean stranding events, and stranding events with causal links to seismic activity have been indicated in Humpback whales, Minke whales and beaked whales by Cucknell, Boisseau and Moscrop (2015).
To cut to the chase, the pursuit of non-renewable fossil fuel by way of seismic surveys can produce chronic acoustic, behavioural and physical disturbance across the entire marine ecosystem.
EFFECTS TO CLIMATE CHANGE
Despite 98% of South Africa’s Exclusive Economic Zone (shoreline to continental shelf and beyond) being subject to a right or lease for offshore oil and gas exploration or production at the time, the South African government ratified the Paris Agreement on Climate Change*. Should the offshore wells produce the promised 9 billion barrels of oil, it would contribute an additional 3.9 billion tonnes of carbon dioxide emission to the atmosphere. This means South Africa won’t be able to meet our peak, plateau and decline greenhouse gas emission commitments to the global economy and we will fail our Paris agreement obligations.
 Shinovene I (2013) Govt fears tuna depletion as oil and gas exploration chase fish away, The Nambian, Nambia (25 November 2013) at:http://www.namibian.com.na/indexx.phparchive_id=116959&page_type=archive_story_detail&page =1