SEA BRIGHT, N.J. - In an effort to help two pods of wayward dolphins, federal scientists put microphones in a river near the Jersey Shore to record sounds that might be scaring them from heading back out to sea.
The recordings will be analyzed this week as scientists continue to monitor about a dozen bottlenose dolphins that they are leaving in the Shrewsbury and Navesink Rivers unless the animals appear to be in imminent danger.
The National Oceanic and Atmospheric Administration put underwater microphones near the Route 36 bridge between Sea Bright and Highlands and one in the Shrewsbury River on Oct. 30, spokeswoman Teri Frady said.
The first round of data was removed from the devices last week. The goal is to see whether sounds on the tape correspond to the dolphins' behavior over three days last week.
A key question is whether construction work on the Route 36 bridge, a major thoroughfare to and from the northern Monmouth County oceanfront, is scaring the dolphins or discouraging them from heading back out to sea.
The dolphins passed under the bridge in early June on their way to the rivers, where they have been feeding and frolicking, and must go back the same way to reach Sandy Hook Bay and the ocean.
Animal advocates have wanted for months to coax or shoo the animals out to sea. They worry that waiting too long could lead to a replay of what happened in 1993, when four dolphins died after lingering too long in the Shrewsbury River. Ice closed in on them, and they drowned.
Two dolphins from the current group - originally put about 15 - have already died.
Yesterday, six dolphins were seen in the Shrewsbury between Sea Bright and Rumson, in a spot where they have spent much time. Several leaped straight out of the water, then splashed down horizontally. One slapped its tail on the water.
Bob Schoelkopf, codirector of the Marine Mammal Stranding Center in Brigantine, said the leaping could be playful behavior related to feeding, or a sign that the animals were trying to shake off parasites.
The tail slapping is more worrisome because it shows distress, he said.
"They're not happy when they slap their tails," he said. "That's a sign of annoyance."
The stranding center and NOAA disagree about what to do with the dolphins. The federal agency, which has jurisdiction over the animals and control over the center's animal rescue permit, has decided that trying to move the dolphins would be too risky.
The agency plans to intervene only if the animals strand themselves, show signs of serious illness, or are otherwise in imminent danger.
Schoelkopf said the water temperature was dropping. It was 52 degrees Monday, down from more than 58 on Oct. 27.
Federal officials say they hope that when water temperatures fall, the bait fish the dolphins survive on will leave the river and the dolphins will follow.
Frady said the observers had found the dolphins behaving normally, feeding on bay anchovies and menhaden. They counted the same 12 that were there at the end of October, when the decision not to intervene was made, she said.
