The federal government proposed rules Thursday that would allow the use of “seismic air guns” and other methods of exploring the ocean floor off a huge swath of the southeastern United States for the first time in decades.

The move is seen as a step toward a possible battle over offshore drilling for oil and gas there in the latter part of the decade or beyond.

Nine companies have applied for permits to use the loud devices to determine how much fossil fuel lies beneath the water in a 330,000-square-mile area from the mouth of Delaware Bay to just south of Cape Canaveral, Fla., according to Tommy P. Beaudreau, director of the Bureau of Ocean Energy Management, which issued Thursday’s environmental impact statement.

Conservationists have questioned the need to explore for oil and gas in the Atlantic Ocean and contend that blasts from the air guns harm marine life.

The area is off-limits to oil and gas exploration until 2017, but President Obama’s successor could lift that restriction. The BOEM estimates there are 3.3 billion barrels of oil and 31.3 trillion cubic feet of gas off the East Coast, but that assessment was done in the early 1980s using technology that is now outdated.

Video



The underwater mapping also can be used to find the best sites for offshore wind turbines and sand deposits for beach replenishment.

Beaudreau said the agency’s preferred rules “are designed to eliminate or mitigate the potential effects of such activities” on marine mammals, fish, sea turtles, birds and bottom-dwelling life.

The air guns, towed behind vessels on the ocean surface, emit blasts of compressed air that are as loud as a roaring jet engine. The pulses must be issued every 10 or 15 seconds for days, weeks or months at a time to produce reflected sound that is used to map what lies beneath the ocean floor.

Marine mammals such as whales that rely on sound for navigation are sensitive to such blasts of sound, conservationists say. To protect the endangered North Atlantic right whale and nesting turtles, the rules would prohibit use of the air guns in certain areas and at certain times during migration and nesting periods.

Vessels would be required to employ passive acoustic technology to determine when marine life is nearby instead of the visual spotting that was relied upon in the past.

Video



Oceana, a leader of the fight against use of the devices in the Atlantic, said the November -to-April ban on the use of air guns within 20 miles of the coast is insufficient to protect the right whale, said Matt Huelsenbeck, a marine scientist with the group. He said the BOEM should have used updated acoustic standards developed by the federal government and should have better investigated alternative technologies.

“Doing the seismic testing, the administration is taking a big step to allowing offshore drilling in the future,” he said. “We shouldn’t be looking for things in the Atlantic and putting all these animals at risk.”

Chip Gill, president of the International Association of Geophysical Contractors, said in a statement that the organization is reviewing the BOEM’s study to ensure that the restrictions “are proportionate to the level of risk of impact to marine life and based on sound science.”

Beaudreau stressed that before any contractor could conduct a survey, it would face the possibility of additional restrictions as part of the permitting process.