NavesinklocustThe view downriver from the Oceanic Bridge, the route the remaining dolphins would need to travel to reach the Shrewsbury River and, ultimately, Sandy Hook Bay.

Federal marine experts this afternoon outlined two acoustics-based approaches to moving the remaining bottlenose dolphins out of the Navesink River before they become stranded inland for the winter.

Scientists with the National Oceanic and Atmospheric Administration said they’ll first trying luring the animals out to Sandy Hook Bay, and possibly out to sea, using a prerecorded sounds of other dolphins feeding and interacting socially.

Plan B, should the “pied piper” effort fail, would be to herd the animals by broadcasting disturbing sounds upriver of the pod, driving it downriver.

A third option, of capturing the individual pod members, is also under consideration, though the experts said the risks there would be greater both for the animals and the humans involved.

At the moment , though, no firm timetable for any removal effort is in place, they said. It will depend on the health conditions of the dolphins, the availability of prey, water temperatures, and the relative location of other bottlenose migrating south in the Atlantic Ocean, said spokeswoman eri Frady of the National Oceanic and Atmospheric Administration‘s Fisheries Service.

“The seasons are changing, and we would expect the dolphins in the Navesink to leave soon,” said Frady. “However, should they need to be moved, we certainly want to do that while they are still fit and have a good chance of surviving.”

Rumson_dolphinsDolphins on the lee side of the Oceanic Bridge on July 9, two days after they were first spotted in the Navesink.

A telephone press conference today followed a phone meeting between NOAA officials and outside experts about the general outlines of an intervention and what might trigger it, Frady said.

“We have not set a specific date or decided if we will do a herding, but if we do it, it will happen soon, probably within the month,” she said.

Stepped-up monitoring of the remaining 7 to 10 animals will start next week, and will include extensive photographing to help determine their health conditions.

The pod, which was first reported in the Shrewsbury River on Father’s Day and moved into the Navesink near the Oceanic Bridge on July 7, was officially estimated to include 16 members this summer. Except for two juveniles that were found dead in the past two weeks, the scientists said they don’t know where the other dolphins went.

Both the luring approach, which one expert said has not been widely used, and herding plans would require the use of boats and equipment strung across the southern access of the Shrewsbury River to prevent the dolphins from going farther away from the bay. Once scientist called it “a wall of sound.” Far fewer vessels would be used in the luring approach, however.

The experts also agreed it would be “helpful” if no pile driving or other heavy construction noise was present at the site of the Highlands-Sea Bright Bridge reconstruction project, and said they are coordinating with other agencies to make that possible.

Introducing a note of caution, however, Brandon Southall, an ocean acoustics specialist at NOAA, said that “it’s possible the animals could ignore both [luring and herding] signals and that neither is going to work. We’ve had past situations where the animals don’t do what you’re trying to get them to do.”

Another scientist said that while panic among the animals is possible, the herding approach would be designed to avoid that outcome.

Herding has been commonly used in the Cape Cod area and elsewhere in New England to head off imminent mass strandings, the experts said. But they added that this case is unusual given the distance the dolphins have traveled upriver and the fact that they appear to have set up house on the lee side of the Oceanic bridge.

“I think it makes it somewhat more difficult,” said Southall. “They’ve been living and feeding there for some time.”

The stocks of menhaden in the river remain abundant, fishermen tell redbankgreen.

As for the rationale of intervening, Randy Wells, a senior conservation scientist and dolphin research program manager for Chicago Zoological Society & Mote Marine Laboratory, said dolphins are highly adaptable to changing prey conditions and location. But animals sometimes make mistakes and need to be put back on the right track, he said.

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