Durban - A French oil and gas exploration company is preparing to blast sound waves into the sea for 24 hours a day off the KwaZulu-Natal coast next year, raising fears about how intense underwater noise could affect fish and other creatures.
The seismic survey would cover 80 000km² between Port Shepstone and Mozambique.
The underwater noise, at about 230 decibels, would continue day and night for up to four months, in an environment where many sea creatures have evolved to rely on sound as their main sensory system.
Equipped with up to 70 airguns, the survey vessel would fire sound blasts every 10 to 20 seconds to a depth of up to 2.5km to build up a sound-based picture of the ocean floor on behalf of Sasol Petroleum and a Singapore company, Silverwave Energy.
A Cape Town company that has compiled an environmental management plan for the oil companies, has rated the potential impacts as “very low” or “low”, but marine scientists have painted a less rosy picture.
For example, the scientific committee of the International Whaling Commission cautioned seven years ago that seismic surveys (combined with the noise of ships and military sonar) were cause for “serious concern”.
The committee said there was a noticeable increase in the number of humpback whales being stranded along the coast of Brazil and grey whales fleeing their feeding grounds near Sakhalin Island during seismic surveys.
In North America, scientists found that crabs showed evidence of tissue and organ damage, while the growth of crab eggs was retarded.
Other studies found catches of several fish species dropped temporarily, by as much as 50 percent, in the vicinity of seismic surveys.
A scientific review in the Marine Technology Society Journal reported a wide range of potentially serious damage to fish and mammals.
This report noted that some bony fish with air-filled swim bladders were particularly vulnerable to damage from intense sound and that many avoided areas where seismic surveys were under way.
Whales, seals, dolphins and other deep-diving mammals also ran the risk of decompression sickness or stress from a lack of oxygen if they had to swim away or surface too quickly to avoid loud blasts of sound.
Permanent or temporary loss of hearing was another major concern, especially for marine creatures which depended on sound to find food, to navigate, find mates or avoid predators.
Sperm whales are believed to use echolocation to find food, raising concerns that they could stop eating.
Whale and dolphin calves would be unable to suckle if they were separated from their mothers because of high noise levels.
Scottish sea mammal expert Jonathan Gordon expressed fears that the long-term, indirect and subtle effects of seismic surveys could be worse than the visible and dramatic death of fish and animals from fishing or hunting.
The biggest fear was that seismic air guns and other human-induced noise could prevent sea animals getting to their feeding grounds, increase stress levels, disrupt migration and breeding and ultimately reduce their ability to reproduce.
To address these concerns, consultants CCA Environmental has recommended that the seismic survey should begin in March next year to avoid the peak turtle nesting and whale migration season. The survey company should also use a “soft-start” procedure in which the airgun sound was ramped up gradually to warn sea creatures before the main blasting started.
Trained observers should keep watch from the survey ship and request a halt if they noticed a “mass mortality of fish” or the death of or injury to turtles, whales, sea birds and other creatures or other “obvious negative changes” in marine life.
If observers requested a halt to the firing it was important that they should be aware of and “have a full understanding of the financial implications of terminating firing”. - The Mercury
l The public has until November 4 to comment on the draft environmental management plan for the survey.
For more information, contact Eloise Costandius of CCA Environmental at 021 4611 189; e-mail [email protected] ccaenvironmental.co.za or visit www.ccaenvironmental.co.za.