Dolphins on the west side of the Oceanic Bridge in mid-July. (Photo courtesy of Mary Fenton)

A team of experts from the National Oceanic and Atmospheric Administration has decided that the dolphins in the Navesink and Shrewsbury rivers are just doing what dolphins have done for millions of years and there’s no urgent reason to try to get them to leave.

Still, acoustical measurements and other forms of observation are being stepped up to determine if construction work on the Highlands-Sea Bright Bridge might serve as an obstacle to the dolphins’ exit if and when the animals decide to leave, they said.

Otherwise, the marine specialists have concluded that two intervention plans discussed in recent weeks are unlikely to work. One involved luring the dolphins out to Sandy Hook Bay by playing back recordings of prey or other dolphins socializing; the other contemplated driving them downriver using harsh noises.

NOAA now believes that the dolphins would probably ignore never-tried luring sounds, given that they’re still enjoying plentiful stocks of menhaden in their present habitat. The herding approach is considered high risk, likely to result in fragmenting of the pod, strandings and deaths.

“We are saying the wisest thing to do is let the dolphins stay there,” said Teri Rowles, lead veterinarian for NOAA Fisheries Service and leader of the National Marine Mammal Health and Stranding Response Program.

Moreover, there’s reason to believe that the pod of Atlantic bottlenose dolphins could survive a cold winter in the river, as long as prey remain plentiful and the dolphins maintain their health, which is believed to be good, the experts said near the end of an hourlong telephone Q&A with reporters this afternoon.

“We do have cases where dolphins have overwintered in places that were unexpected and north of where they would normally be, even in areas in which their was ice in the river,” said Rowles.

Katie Touhey, who heads the Cape Cod Stranding Network, said groups of dolphins have overwintered and even taken up multiyear residence in Virginia rivers, leaving only after they’d depleted the stocks of large prey fish.

“The water temperatures were quite low,” she said, though she was unable to say if any of those rivers had frozen solid.

Larry Hansen, chief bottlenose dolphin researcher and protected species branch chief at NOAA’s Southeast Fisheries Science Center, said the “big picture” includes the fact that the huge stocks of menhaden on which the dolphins fed all summer remain large and may get larger as the prey move inshore.

If NOAA was to drive or lure the dolphins out, “they’re likely to go back into the river again,” he said. “It seems clear that these dolphins used to occupy that river on a regular basis… and so they need to learn how to get out of that river. Because they’re going to go back in there next year and probably the year after and the year after. So they need to regain their cultural memory so they know how to get out.”

NOAA has a press release on the decision.

And here’s a recording of the full press conference:

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