Coast Guard officials are investigating a series of bizarre marine band radio calls along Florida’s Gulf Coast that appear to threaten the sea service’s personnel, vessels and aircraft.

On Thursday, authorities released to Navy Times a recording of an Aug. 13 transmission lasting 70 seconds that originated on VHF channel 22A and apparently was directed at watchstanders at the Coast Guard Sector St. Petersburg command center.

“Attention all Coast Guard stations. I say again, attention all Coast Guard stations," it began. “The next time you scramble any aircraft off of any aircraft carrier, we’re going to ban your (expletive). Do you understand me?

"No. 2, the next time you send off any aircraft off of any aircraft carriers, or helicopters, I will set off all the depth charges in the Gulf and sink your ships. That’s No. 2. No. 3, you are to close down all airports of America, otherwise I’ll set off the depth charges.

"No. 4, the next time I see one of your planes in the air, I’m going to shoot that plane down and kill the pilot and the passengers. That’s No. 4. And I’m going to shake your ships all apart with the depth charges.

"You are playing with the Russian government. I’d suggest you back the (expletive) off. Because if you don’t back the (expletive) off, you’re going to lose a lot of Coast Guardsmen. Do you understand me? Keep your (expletive) airliners and you keep your ships (indecipherable).”

The message is spoken by a gruff male American voice, without a Russian accent. And his threats hearken back to an earlier form of maritime warfare — with anti-submarine depth charges dropped in the Gulf.

As for aircraft carriers, the Coast Guard doesn’t operate them.

Authorities believe that it’s the same voice in a previous transmission that began by saying “Mayday!” three times before discussing “scrambling all jets, we are under nuclear attack.”

There have been at least two calls in August, with the earlier broadcast listing grid coordinates that made no sense, but investigators are listening to earlier messages sent over the past several years that were less distinct, perhaps just a fake “Mayday” warning.

Those sorts of radio calls are more concerning to the Coast Guard because they must respond to emergency transmissions that seem plausible.

“Hoax calls are costly to the taxpayer and our service,” said Charles “Marty” Russell, resident agent-in-charge of the Coast Guard Investigative Service office in St. Petersburg, in prepared statement emailed to Navy Times.

“When the Coast Guard receives a distress call, we immediately respond, putting our crews at risk, and risking the lives of boaters who may legitimately need our help.”

People who are convicted of making false distress calls face up 10 years in prison and $250,000 in fines, plus reimbursing taxpayers for the cost of the searches.

Public Affairs Specialist 1st Class Ayla Kelley said it’s been difficult to pinpoint where the broadcasts originate.

The Coast Guard spokeswoman compared tracing the man’s transmissions to the spaghetti model used to predict the path of a hurricane. These strands drape over a large swath of Manatee and Pinellas counties, which could put the radio in Tampa Bay, out in the Gulf, inside a marina or even ashore.

“The August ones involved Russians and bombs in the ocean. Those seem to be topics in his wheelhouse,” Kelley said.

So she’s urging anyone who has information that can identify the hoax caller to contact Coast Guard Investigative Service agents in St. Petersburg at (727) 535-1437 extension 2308.