SEA BRIGHT, N.J. - Early last June, a group of 16 bottlenose dolphins took up residence in a river at the Jersey Shore. Then winter closed in and a little more than half made it out alive.

Some worry it could happen again after six dolphins appeared in the same river on Sunday, almost a year to the day later.

Wildlife authorities and marine mammal volunteers are trying to get better photos of the dolphins' dorsal fins to determine whether these six are part of the pod that created such a stir last year.

The presence of the dolphins in the Shrewsbury and Navesink Rivers in 2008 pitted the National Oceanographic and Atmospheric Administration against volunteer rescuers in a dispute that played out for more than six months as the animals' numbers dwindled.

Volunteers led by Brigantine's Marine Mammal Stranding Center recalled past instances in which dolphins ventured into the river and stayed into the winter, only to die when ice closed in on them. They wanted the animals coaxed or scared out of the river back into the ocean.

But NOAA scientists, who have jurisdiction over the mammals, argued the dolphins appeared to be trying to extend the northern range of their winter habitat and should be left alone, even if some died.

At least six did, and a seventh dead dolphin was suspected of having been part of the pod.

Teri Frady, a NOAA spokeswoman, said yesterday that the renewed presence of the dolphins in the Shrewsbury bolsters the agency's theory.

"This certainly does support that hypothesis," she said. "We hope the community will embrace them if they do stay. We learned some lessons last year about the need not to approach them and to give them room."

Frady said the agency has received anecdotal reports of large groups of dolphins spotted in the Raritan Bay - near where the Shrewsbury begins - as well as off Jones Inlet on Long Island, N.Y.

"This is the time of year when it's likely we'll see large numbers of dolphins in the area," she said.

Bob Schoelkopf, a director of the Marine Mammal Stranding Center, said he was concerned about the latest group.

"If they strand, we will respond," he said. "We'll see what happens."

Frady and volunteer observers said the dolphins spotted Sunday were doing the same thing as last year's pod: swimming back and forth between two large bridges over the river in Sea Bright.

The dolphins were not spotted yesterday morning, according to state police, whose marine division is responsible for keeping boaters from getting too close.

"Maybe it's a quick-hit in-and-out thing this time," Schoelkopf said. "We have seen that before. Let's hope."