Investigators are checking the possibility that the calls came from the same man, Coast Guard Capt. Gregory Hitchen said. A voice expert has been analyzing the calls.
In New Jersey, a reported June 11 explosion aboard the super-yacht Blind Date off Sandy Hook prompted a massive effort by emergency responders that cost more than $335,000, authorities said. The caller said 21 people were aboard, of whom three had died and nine were injured.
In Texas, another major rescue effort to locate the six people from a sinking fishing boat May 20 near Galveston also cost thousands of dollars. A more precise cost estimate has not been determined.
In both incidents, no evidence was found the vessels existed.
The Mayday calls may be examples of a practice known as "swatting," in which pranksters make hoax calls to authorities, then brag about them on blogs, the FBI said.
The Coast Guard is seeking the public's help in the investigation and has offered a $3,000 reward for information leading to an arrest and prosecution.
The caller in the New Jersey and Texas cases "used the same terms," said Coast Guard Petty Officer First Class Thomas McKenzie, a spokesman with the guard in New York.
He spoke of orange life rafts and said his antenna was down, making it impossible to provide a precise position.
The "voice and manner of speaking were similar," Coast Guard officials said in a statement after a news conference in New York City.
The calls for help, it was later determined, seemed to originate from land, investigators said, and were made to the Coast Guard Vessel Traffic Service rather than to the service in general, which would be more natural, or to the known emergency frequency, VHF Channel 16.
The caller provided "very specific locations of distress and distances, while at the same time exhibiting throughout the calls unfamiliarity with the area and/or using references to location that a boat captain typically wouldn't use," officials said in the statement.
Hoaxes are not only costly, Hitchen said, but they also "divert assets from real emergencies."
The responders involved in the New Jersey rescue efforts included two Coast Guard boat crews and four guard aircraft crews, as well as response units from New York City Police and Fire Departments, New Jersey state police, and the Nassau County (N.Y.) Police Department. Civilian vessels also joined in.
While seeking the supposed survivors of the Blind Date, the Coast Guard also received a distress call involving a person in the water off Bayonne.
Personnel were available to look and found no one. But the guard would have had a more difficult time trying to respond to a more serious situation, Hitchen said.
In Texas, the Coast Guard "became suspicious that [the] call was a hoax because of a few oddities," said Capt. Ed Cubanski. But "we continued to search on this case with the typical zest and vigor we search on all search and rescue cases."
Solving hoax cases presents a challenge, especially without witnesses, Hitchen said. But the perpetrators have been known to "brag about it," the captain added, and that could give investigators the break they needed.
Contact Edward Colimore at 856-779-3833
This article contains information from the Associated Press.