In this April 16, 2014 file photo, a member of the Army Corps of Engineers looks on as a finback is whale is secured before being pulled out of the water on a dry dock in Jersey City, N.J., after the whale was found dead in New York harbor over the weekend. The National Oceanic and Atmospheric Administration says the rate of strikes is higher than usual for this time of year. (AP Photo/Julio Cortez, File)

A cruise ship heading for New York this month struck and killed a whale and dragged it into the Hudson River, part of a higher-than-usual rate of strikes along the Eastern Seaboard for this time of year, a federal agency said.

There were three recent whale strikes recently, including one in which a cruise ship hit a sei whale and did not discover it until it reached port, the National Oceanic and Atmospheric Administration said.

In a similar case, a sei whale was found dead and attached to a container ship that was docking near Philadelphia, NOAA said.

The whales may be following food sources closer to shore, NOAA said. An increased food supply has recently been cited for a large increase in the number of humpback whales off Massachusetts.

The agency issued a reminder to mariners of measures already in place to protect whales, including speed limits and distances.

"Nobody wants to hit a whale," said Marjorie Mooney-Seus, a spokeswoman. "So we want people to have a greater awareness that they're out there now."

The usual rate of whale strikes by ships is about one every few weeks, she said, compared with the three in the past few weeks.

In this April 16, 2014 file photo, a deceased 55-foot long finback whale sits on a dry dock in Jersey City, N.Y., after it was pulled out of the water. A spokesman for the Marine Mammal Stranding Center said it is not uncommon for whales to make their way into shipping lanes as they travel up and the down the East Coast, though they don't usually stray into the harbor. According to the National Oceanographic and Atmospheric Administration, the number of whale strikes is unusually high this year. (AP Photo/Julio Cortez, File)

NOAA said it counted 28 whale strikes in Northeastern waters between 2006 and 2010. Worldwide, a National Marine Fisheries Service survey covering 1975 through 2002 found 292 records of confirmed or possible ship strikes to large whales.

Rob DiGiovanni, who heads a marine mammal rescue group on Long Island, said he's seeing "more evidence of ship strikes and that's definitely a concern." In the past, his Riverhead Foundation for Marine Research and Preservation would go a couple of years without seeing a large whale that had been hit by a ship.

"Now we get a couple a year," he said.

The New York cruise ship incident was discovered May 4, the Philadelphia case on May 7, Mooney-Seus said. She did not have details about the third recent strike except that it involved a fin whale; NOAA is investigating.

A necropsy on the New York whale found it was killed by blunt force, confirming that it was killed by the ship, Mooney-Seus said. The other two whales were not retrieved.

In this April 16, 2014 file photo, marine biologists conduct a necropsy on an over 55 foot long finback whale on a dock in Jersey City, N.J. The whale was found stuck on the bow of a container ship in the harbor on April 12, and later towed to an Army Corps of Engineers station near Liberty State Park. The frequency of whale strikes is higher than normal for this part of the year according to the National Oceanic and Atmospheric Administration. (AP Photo/Julio Cortez, File)

NOAA said there have been no recent reported strikes of endangered North Atlantic right whales.

DiGiovanni said his group hopes to study whether the numbers are up because there are more whales, more ships or a change in a food source, as suggested by NOAA.

In the coastal waters off Boston, large numbers of a fish called the sea lance have turned the mouth of Massachusetts Bay into a "whale feeding ground," said Laura Howes of Boston Harbor Cruises.

Twenty to 30 whales are being spotted on every whale watching excursion, 10 times the usual number.

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