BRIGANTINE, N.J. (AP) – Hooded seals, bottlenose whales and a manatee have been spotted in the waters of the northeastern U.S., leaving marine biologists puzzled as to why they have strayed from their natural habitats.

The presence along the Jersey Shore of mammals who normally swim in much warmer or colder waters took a troubling turn recently with the discovery of three of the seals on New Jersey beaches. All were suffering from starvation or exposure.

Those seals and two others found in North Carolina and Virginia – all of them pups about six months old – are being cared for at the Marine Mammal Stranding Center. The center has never had to rescue any in the summer months before, according to founding director Bob Schoelkopf.

The sudden influx has Schoelkopf and others searching for clues.

“We’ve never had this rate of strandings in the summer months, and we really have no definitive idea why it’s happening,” Schoelkopf told The Philadelphia Inquirer. “And why these animals are turning up in all these strange places. It’s truly a mystery.”

The bottlenose whales, which normally are found in the North Atlantic, have also been sighted along the East Coast, Schoelkopf said. And a manatee, whose habitat is chiefly the warmer waters off Florida, made its way up the Hudson River through New York City this month and was last spotted off Cape Cod.

Studies conducted by the Woods Hole Oceanographic Institute in Massachusetts and the Scripps Institution of Oceanography at the University of California at San Diego suggest the strange migrations could be attributed to underwater noise created by long-range sonar testing conducted by the Navy and to expanded global shipping.

Whales, dolphins and other marine mammals use sound signals to mate and communicate with each other and may be misreading the man-made sounds.

“We’re very concerned about this because we think the research is clear that the sonar testing can have an adverse impact on the marine environment,” said Michelle Duval, a senior scientist with Environmental Defense, a Washington-based nonprofit advocacy group.

The group has opposed the establishment of a 500-square-mile sonar range in the Atlantic Ocean off the North Carolina coast.

Navy officials said the studies don’t prove any long-term effects of sonar on marine mammals.

At the Brigantine facility, one of only a half-dozen federally licensed centers on the East Coast that aid stranded mammals, resources are being strained as workers dip into reserve supplies of fish to feed the seals.

If the seals survive, they will be taken to Maine and released into the North Atlantic.