The Noise about Seismic Testing
Human underwater noise could be harming marine life and it is an issue of growing concern. Human ears are really lousy underwater as we are evolved to hear in air, but for a marine animal the ocean is full of sound. We know that whales and dolphins rely heavily on their hearing, but that’s not the full picture. According to one defense scientist, “You have choruses where the whole background noise rises by 20 decibels – it’s like the cicadas in the trees. Many fish have swim bladders that they can drum or strum, it’s a very efficient source of sound. And shrimps make a lot of noise.”
Humans can make a lot of noise too with ships, scientific instruments, defence exercises and construction work. That could interfere with animal feeding, breeding and migration behaviour. Oil and Gas The new “noise pollution” issue on everyone’s lips at the moment is oil and gas seismic testing, which uses repeated underwater sound blasts to map potential oil and gas reserves. Recently, oil companies are ranging further and deeper in search of oil. In Australia, professional fishermen have recently claimed that “anecdotal and scientific evidence” suggested the testing could affect stocks of black jewfish, arrow squid, scampi, blue warehou, orange roughy, gemfish and the loggerhead turtle. A southern bluefin tuna quota survey in the Great Australian Bight showed tuna numbers crashing from around 22,000 tonnes to 3000 tonnes at the same time as BP conducted a seismic survey. Numbers recovered when testing ceased. In 2011, NT fishermen also protested testing and claimed “We have proven drops in fish catches from previous surveys, where fisheries have now actually been through the data and can demonstrate that our catch rates have dropped”. A study from the Faroe Islands showed that although 75% of the fishermen interviewed claimed a detrimental effect on fishing in the neighbourhood of seismic activity, there was no evidence of a catch decline in their logbooks.
The Australian Petroleum Production and Exploration Association said “…more than five decades of experience and research shows no evidence that sound from oil and gas exploration activities causes injury to marine species …” “And unlike the activities of other industries [such as fishing itself], there is no scientific evidence that would suggest oil and gas exploration activity has detrimental impacts on fisheries or fish stocks.”
Ouch, we should also note that commercial fishermen also use high power output fish finders and side scan sonars. Even small boats have fish finding and echo sounders with characteristics broadly similar to high frequency military sonars. Defence Uses Another controversial source of “noise” have been the acoustic devices used by defence agencies to detect submarines. Claims of whale strandings caused by the military are frequent and these conclusions are generally rejected by authorities. Despite not doing a lot of noisy exercises, the Royal Australian Navy (RAN) has been quick to recognise the potential of the issue. The ‘Behavioural Response of Australian Humpback whales to Seismic Surveys’ program is the largest project in the world on the effects of noise on whale behaviour. It’s partly co-funded by the oil and gas industry and US Government regulators. For noisy activities at sea, such as seismic surveys and naval exercises, the impact of noise is usually managed by having an exclusion zone around the noise source. Observers look out for marine mammals and can halt operations. Exclusion zones are based on limited information and there is concern, even within the RAN, about whether or not they are the most effective measures. “We’ve found that [whales] react at levels which are right down near the background noise when exposed to tonal sounds”. However, that may not have longer-term consequences. “But if it’s something that causes animals to, say, move away from where they normally feed, that might have a longerterm effect”. These long-term effects are going to be the subject of a lot of further study. Scientific Uses Even scientists get into trouble over noise. Researchers often use sound to predict earthquakes, employing long submersible cannons called airguns. Testing by Geoscience Victoria for possible carbon storage areas below Bass Strait in 2010 is alleged by fishermen to have killed 24,000 tonnes of Bass Strait scallops, worth $70 million. Surveys of a control area before and after the seismic survey did not detect any changes in the abundance of live scallops, or their condition or size in the period less than 2 months after testing. The CSIRO found no biological causes, but natural die-backs are not uncommon with this species. The sound of an airgun explosion is reputedly 265 decibels at the source, and 110 decibels almost five miles away, too loud for human swimmers, and especially some concerned environmentalists. In the past, explosives were used to create seismic waves, and compared to that, airguns are eco-friendly. Environmental and animal-rights groups acknowledge the need for airguns but insist researchers could do a better job. Scientists have stated they are taking reasonable efforts to prevent harm and the risks are overstated.
In the US the issue has been big news and has been used as a reason to kill politically sensitive development. The Diablo Canyon nuclear power plant was stopped from conducting seismic surveys to assess earthquake risk. Post Fukushima, hackles were raised and the government hearing turned into a public rally. The power company promised that they would compensate fishing operations for any losses, and would spend $8 million on a monitoring program. One protester suggested the testing wasn’t needed to determine that, “A nuclear power plant on a fault line is dangerous. Period.” The commission unanimously agreed and the decision was greeted with cheers from hundreds of environmentalists and commercial fishermen.
Do marine critters react to airguns? It depends upon which study you prefer, but the answer seems to be “often No”. There is some evidence that very few fish species can detect noise at a distance of greater than 15 m. A 2003 Norwegian literature review concluded that testing will have variable but relatively small impacts on the behaviour of trawl fish. Some fish were scared off temporarily, other much less so. Research in Scotland showed that fish had stronger reactions to a plume of air or mud than from the airgun pulse. Airguns could cause a fish egg and larvae mortality rate of 0.018%, which is way smaller than the natural mortality rate of 5 – 15 % per day. A recent UK study found that large crabs experienced stress when exposed to ship noise, but if it became frequent they soon adjusted to it. Since then, studies on crayfish reactions in Victoria (admittedly on sites some distance from intense testing) showed no impacts affecting the catch rate. The impact of seismic surveys is likely to be more sensitive during spawning or migration. A safe zone of a few kilometres has previously been seen as adequate.
Whales may well be a special case and there is some evidence that they do experience noted long-term stress from noise pollution. Baleen whales communicate at 20 to 200 hertz, the same wavelengths as emitted by the propellers of many big ships. Some species have adjusted to this by emitting louder and more frequent acoustic signals. After the 9/11 terrorist attack shipping movements fell along the North Atlantic coast for the first time in 50 years, allowing scientists to measure the impact of reduced noise. In Canada’s Bay of Fundy this caused an immediate drop in whale stress hormones. Constant exposure to low-frequency ship noise may cause chronic stress in whales and reduced reproductive success.
While trying to seem whale friendly, our Federal government hasn’t wanted to harm the energy sector. BHP has been allowed fairly broad scope to explore the Great Australian Bight. Recently, the Federal government approved testing southwest of Port Campbell. It will occur in November and December 2013, in an area known to be frequented by endangered blue whales. The Government says special conditions will be enforced during testing to protect migrating whales. Seismic testing is also proposed for the Kangaroo Island Canyons region in March 2014. Summary The jury is still out. Noise is clearly a relevant issue for the management of marine ecosystems, although its impacts are variable. In many cases it may be able to be managed with a few prudent measures. Like many things to do with the sea, the data is noticeably incomplete and we could do with a lot more study in this area.