WHL Energy will begin its search to size up reserves in the untapped La Bella gas field next week after gaining federal government approval to use high-powered sonar equipment. 

But fishing and conservation groups warn the testing will harm marine life. 

Apollo Bay cray fisherman Russell Frost said the industry had only been consulted once, 18 months ago, despite concerns that the noise testing could harm growing crayfish larvae. 

“We think it’s going to have a huge impact,” Mr Frost said. 

“The last time they did testing in the Bass Strait we noticed a real demise in our stocks.” 

Crayfish take five years to develop into adults.

“The crayfish are just spawning. The eggs are floating up in the water column. They’re probably at their most vulnerable right now.” 

Mr Frost said autumn would be the best time to carry out the testing, once the larva were stronger. 

The International Fund for Animal Welfare (IFAW) is also maintaining opposition to testing it says will have a “deafening” impact on whales, forcing them away from feeding areas.

WHL agreed to test in seasons when species such as the southern right whales had left the region. 

But IFAW campaigner Matthew Collis said record numbers of blue whales were spotted off the south-west coast nearly a year ago. 

Director of the Portland-based blue whale study group Dr Peter Gill said some overseas reports had pointed to the ocean giants being disturbed by the sonar noise.

“There’s still a lot not known about this issue. The frequency range of seismic testing is the same used by blue whales so there is potential there for acoustic impact,” Dr Gill said. 

“It’s hard to study. It’s very difficult to disentangle natural behaviour from other effects.” 

The group is waiting on additional funding from gas companies to do more observation work. 

WHL Energy maintains it has adopted best practice. 

If whales approach within two kilometres of the ship,  testing will be switched to the lowest gear, while a stricter three-kilometre, low-power rule applies for blue whales. 

Seismic testing will be turned off altogether if the marine giants come within 500 metres. 

Company spokesman Colin Hay said four whale observers would be used on a survey vessel.

Mr Hay said there had also been a series of studies on crustaceans that found “acoustic sound impacts to early life stages on crustaceans (Dungeness crab) …identified that there was no difference in the immediate survival rates or long-term survival rates”. 

Another study in 2006 found the same results for rock lobsters.