"From the air, most appear to be dead," he told reporters on Wednesday.
Further assessments of their condition will be undertaken.
"It's a good distance from the stranding we've been focused on and not necessarily a place that is obvious for a stranding," Mr Deka said.
"The water is a very dark tannin colour. Potentially they stranded, washed back into the water and then have been washed back into the bay."
Source: Sarah Maunder/SBS News
Rescuers have been able to guide about 30 whales from the initial group back out to sea but several of those have again become stuck.
About a third of the 270-strong group are believed to have died, with more information expected to be known about their condition later on Wednesday.
Experts have labelled the operation "one of the trickiest" due to the number of animals and unique tides in the area.
Marine Conservation Program wildlife biologist Kris Carlyon said the highly social pilot whales could be heard calling out to each other in distress.
The pod may have been drawn into the coast to feed or by the misadventure of one or two, he said.
Authorities are also deliberating how to handle the grim task of getting rid of the carcasses.