Research finds buffer zones can help mitigate damage to Southern Rock Lobsters caused by soundwaves used in oil and gas exploration

By Gio Braidotti

The drive to find additional sources of oil and gas to power commercial economies is contributing to noise pollution in the oceans, and fisheries are among the sectors affected. That is because 30 per cent of global oil and 27 per cent of global gas production come from offshore deposits (according to 2015 figures).

The way the offshore energy sector and fisheries intersect is the subject of research to monitor and improve practices to minimise ecological impacts.

A recent Commonwealth Senate Inquiry report recommended further research, funded by the Australian Government, to understand “the short-term, long-term and cumulative impacts of seismic testing on marine animals and the marine environment”.

The need for improved science-based knowledge to mitigate seismic sound pollution underpins collaborations involving the FRDC, oil and gas industry partners, and the fisheries sectors, supporting significant research.

Among global leaders undertaking this work are researchers at the University of Tasmania (UTAS) and Curtin University in Western Australia, led by Jayson Semmens, Ryan Day and Rob McCauley.

Semmens is based at the UTAS Institute for Marine and Antarctic Studies, and his key focus as part of FRDC-funded research is understanding and mitigating impacts from seismic surveys.

He explains the seismic surveys produce images of underwater rock formations beneath the seafloor that are needed to find oil and gas deposits and to monitor known fields.

Obtaining these images, however, is far from straightforward.

The industry uses powerful air guns to create blasts of sound for its seismic surveys. “These guns expel air into the water that produces soundwaves that penetrate the seafloor rock. These sound waves bounce off geological structures and the return signals are used to generate images,” Semmens explains.

The air guns have the capacity to expel highly compressed air (between 40 and 150 cubic inches of air), with arrays of different-sized guns used to conduct a survey. The air gun rapidly releases the compressed air, forming a bubble that produces a loud sound that travels through the water to the ocean floor. It is the equivalent of being in the front row of a rock concert.

When this technology was introduced in the 1980s, it replaced explosives and amounted to a gain for marine environments.

Nonetheless, the technology was noted for having two impacts: it generates soundwaves and disturbs seafloor particles, burying organisms or causing stress through limiting light availability.

Soundwave impacts

“There was work done to understand impacts of the sound waves on marine mammals since species of whales and dolphins use sound to communicate,” Semmens says. “However, there was little work done on the impact on fish and invertebrate species. That’s the knowledge gap we are now closing.”

The FRDC has funded a series of projects to investigate impacts on rock lobster, finfish and octopus. The most recently completed project targeted impacts to Southern Rock Lobster (Jasus edwardsii).

That work has made important findings that are having a direct bearing on the way the industry operates and is regulated.

A key discovery is that larval and juvenile Southern Rock Lobsters can recover from soundwave-induced damage if there is a buffer of at least 500 metres to the air guns.

This work was undertaken using a commercial array deployed by exploration company CGG off Victoria’s southern coast in the vicinity of Lakes Entrance. CGG contributed half the funding for this project, as well as a significant in-kind contribution.

The study involved placing captured larval and juvenile lobsters within two distances of the air gun array: zero and 500 metres.

Testing for damage was made possible by findings from a previous study. That work used a single air gun and identified damage to an organ in the rock lobsters that is equivalent to the inner ear cavity of humans. Called a statocyst, this organ contains hair cells that aid rock lobsters in equilibrium and coordination, just as the inner ear helps humans maintain a sense of balance.

“In an earlier project, we found that air guns shear off hair cells in adult rock lobsters,” Semmens says. “That loss impairs the lobster’s sense of coordination and we can measure this impact by testing the ‘righting reflex’ – a test in which the animal is flipped on its back and the time needed to right itself is measured.”

The latest research found that lobsters do not recover from this loss of coordination if exposed directly to an air gun array.

A buffer of 500 metres, however, saw the animals recover once they had moulted their shells, something that juveniles especially do at regular intervals.

Implications for industry

The finding has several important implications.

First, evidenced-based findings are the key driver to improve industry practices and regulatory standards. In Australia, environmental management associated with offshore oil and gas activities in Commonwealth waters is independently regulated by the National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA).

“The need for a buffer zone is something that is likely to be picked up by both industry and the regulator,” Semmens says.

Secondly, the study validated at a commercial scale the findings from earlier work made using a single air gun. Those earlier studies had been criticised for potentially lacking industry relevance. Those concerns have now been put to rest.

As a consequence, this experimental approach (based on a single air gun) can now be used with confidence in ongoing research to further explore impacts on lobsters and how to mitigate them.

The project made an additional finding that has important implications.

The researchers detected that the intervals between moulting increased in animals exposed to seismic signals, going from between 16 and 18 days to between 23 and 30 days, which may result in slower overall growth rates. Unlike the righting reflex, this effect did not reverse in those lobsters exposed 500 metres from the seismic source. The timing of moulting also normally occurs when predators are less likely to be in the environment; the delayed moulting exposes rock lobsters to a greater risk of predation as their new shells are hardening.

Semmens notes all the work of the UTAS and Curtin research team has focused on individual effects, but there is a broader understanding that still needs to be gained.

“Since all our work has examined impacts on individual animals, we don’t yet know the population effects,” he says. “That could be something we look at in the future.” 

New ways to investigate below the seabed

The FRDC is partnering with leading Australian research institutions and other fisheries organisations to fund a collaborative research project to trial emerging seismic survey technologies that will have a reduced impact on marine species.

Led by Beach Energy, the project will assess how eSource™ and distributed source technologies will perform in open oceanic waters. The technologies have shown promise in lakes and water tanks. The work will also research the potential impacts of these new surveys on scallop and lobster.

The trial of emerging technologies and marine species research aligns with the end of another Beach Energy project, the Prion Survey, a three-dimensional marine seismic survey to map the geology beneath the seabed, enabling the assessment of natural gas reservoirs.

Beach Energy