West Coast seismic oil survey a threat to marine food chain

2019-02-18 16:27
Ocean. (Duncan Alfreds, News24, file)

Ocean. (Duncan Alfreds, News24, file)

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A Norwegian company has applied to conduct seismic surveys for oil along the Cape's West Coast using air-gun blasts known to be highly damaging to marine life.

Petroleum Geo-Services (PGS) plans to do 2D and 3D seismic surveys over an area of around 290 299 km2 from Alexander Bay along the West Coast to the Cape Agulhas. The surveys are scheduled to take up to five months, starting in the next few months, reports the Conservation Action Trust.

If Petroleum Agency SA (PASA) issues the permit, the environmental impact could be catastrophic.

Globally, seismic testing on the marine environment has been found to have disastrous effect on zooplankton at the base of the food chain. It has also been linked to whale and dolphin strandings.

Seismic testing is a vital aspect of oil and gas exploration.

Impulse signals

Often conducted beneath the water's surface as part of the geological survey, it entails bursts of intense, low-frequency impulse signals discharged into the ocean by a research vessel using an air-gun system.

The sound waves bounce off geological formations on the ocean floor and are captured by on-board hydrophones. The data is analysed for details about the different types of undersea rocks. This can signal the presence of gas or oil within the rock. formations below.

According to the Environmental Management Plan (EMP), prepared for PGS by SLR Consulting, the plans pose, "insignificant to medium significance", after "impact mitigation measures" have been put into place.

It classifies the potential environmental impacts on plankton as "very low". Other marine animals such as fish, invertebrates, seabirds, turtles and seals are also placed in the insignificant to medium risk category.

PGS says it would use a "soft start" procedure - basically a warning shot to disperse marine life from the immediate area before the survey begins.

It can be assumed that bigger marine animals will swim for their lives. But tiny drifters such as plankton, which depend on the current to carry them to safety, cannot do this. This puts them squarely in harm's way.

The SLR Consulting assessment contrasts with many other findings from research done in Spain, America, SA and in other locations around the world.

Domino effects

Zooplankton underpins the health and productive capacity of all marine ecosystems. An Australian research team found that air-gun operations caused significant losses to zooplankton populations directly after seismic surveys were conducted. A day later zooplankton were still dying.

There was also a domino effect on other species.

A South African study found that during seismic surveys, African penguins avoided their regular feeding area. They returned only after the surveys were completed.  

During seismic testing in 2016 off KwaZulu-Natal, 10 whales beached themselves plus 42 birds, nine turtles, eight dolphins and five seals.

While causality has never been empirically established, it's hard to discount the coincidence, given that there were no other disturbances recorded on the day that could account for such a phenomena.

Other studies have noted various impacts to marine animals which include tissue damage, haemorrhaging and damage to organs that are essential for balance underwater.

Another study recorded altered behavioural impacts on whales.

Read more on:    cape town  |  environment  |  marine life
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