A large tidal turbine bolted to the bed of Strangford Lough is to run continuously through the summer – so the operators can see what happens when seals and porpoises swim close to the blades.
Until now Marine Current Turbines (MCT) was required to shut down the SeaGen turbine when marine mammals swam close to the device in order to make sure they weren't injured.
But the company says it cannot move on to the new stage of developing the renewable technology unless it carries out the three-month experiment this summer.
David Erwin, who chairs the science group that looks at the research being carried out by MCT, said the company has questions that need to be answered.
The turbine is located in Strangford Lough, which has one of the world's fastest tidal currents. It generates electricity from two massive underwater propellers.
SeaGen will be looking at whether marine mammals passing through the Narrows will try to swim straight through the turbine or take evasive action. Until now, sonar scanning the waters around the turbine was examined 24 hours a day by a team of employees and if anything that resembled a marine mammal came within 30 metres the blades were halted.
"We have little idea of how seals actually react to the installation," Mr Erwin told a meeting of the MCT SeaGen liaison group.
"It is vital to know how seals react to the turbines when they are deployed in open sea."
Northern Ireland Environment Agency, a division of the Department of the Environment, has now granted SeaGen a licence that protects it from prosecution if the turbine operation disturbs harbour seals. Because harbour seals are a protected species, it is an offence to disturb them, unless a licence is granted by NIEA.
Members heard that between 1993 and 2007, harbour seal populations in Strangford Lough were declining by an average of 3% a year, but between 2007 and 2012 numbers increased by 10% on average, as revealed by monthly seal counts carried out by NIEA and the National Trust.
The counts also show that grey seal numbers in the lough are much higher than in the 1990s.
DoE marine division senior marine conservation officer Joe Breen said the experiment should provide a better understanding of what the risk of collision is and it will not put the conservation status of the seals in jeopardy.
Strangford is the largest sea lough in the British Isles and one of only three designated Marine Nature Reserves in the UK. Its waters harbour more than 2,000 species. The sheltered tidal waters are host to Northern Ireland's most important common seal population, which can be seen almost all-year round. Small numbers of grey seals are also present and otters frequent the shore.