Controversial fishing trawler Geelong Star is believed to be fishing in waters north-east of Tasmania after adopting more safeguards against killing marine mammals.

The 95-metre freezer factory ship voluntarily suspended fishing after killing eight dolphins and four seals on its first two trips in Australian waters.

The Australian Fisheries Management Authority then restricted its crew to daylight fishing operations only.

Further restrictions mean that if the Geelong Star kills one more dolphin it will be evicted from the relevant fishery for six months.

In a further measure to prevent fatalities, the vessel has now been equipped with a new mesh grid.

Bridport-based boat builder Allan Barnett was confident the new addition would work.

"In front of the opening of the net they've put like a big wall of smaller mesh across the front, so dolphins and seals can't fit through that mesh to go down in the tunnel of that net," he said.

Mr Barnett said the flipside was the grid could hamper attempts to catch fish.

"The problem they might have, and I'm envisaging they probably will have, it might stop the fish from going through too," he said.

"So whether it's still okay with their fishing side of it, I don't know, but from a dolphin and seal point of view it will fix that."

The boat's exact location is unclear because it was given approval to switch off a tracking device to avoid detection by activists.