A young dolphin was found dead in the Navesink River on Wednesday morning, probably from a group of wayward dolphins that made a wrong turn out of Sandy Hook Bay in June, officials said.
It was found by a marina worker in Fair Haven near where a group of 15 dolphins has been staying since early summer, drawing crowds of sightseers but worrying rescue groups that say the approaching winter puts them in grave danger.
The cause of death was not immediately clear; tests were planned.
"We got a lot of enjoyment watching them," said Jim Ceruti, owner of the Fair Haven Yacht Works, near where the dead dolphin was found. "For as good as that made you feel, it hurts even worse when you see one of them die."
The plight of the dolphins has become a point of contention between rescue groups and national wildlife officials, who have been reluctant to approve a plan to coax or scare the dolphins out of the Navesink and Shrewsbury rivers back out to sea.
"Hopefully this animal did not die in vain," said Bob Schoelkopf, co-director of the Marine Mammal Stranding Center in Brigantine. "Hopefully this is a wake-up call to let people know these animals are not going to make it through the winter."
The National Oceanic and Atmospheric Administration has said it would not act to move the dolphins back out to sea unless it appeared they were in danger or becoming ill, partly because a rescue could stress the animals and do more harm than good.
State Sen. Joseph Kyrillos said Wednesday that an agency official told him a rescue plan would be launched, though, if the animals have not left the river by the third week in October.
In 1993, four dolphins who lingered too long in the Shrewsbury River drowned when ice closed in on them and they were unable to get to the surface to breathe.
"The water's getting colder; there's not as much salt in the river now," Ceruti said Wednesday. "Is their food source dwindling? These dolphins are probably stressed now."