ATLANTIC CITY, N.J. (AP) — As the stench of a dead whale hung in the air, environmentalists and opponents of offshore wind stood on a beach where the marine mammal lay buried Monday and called for a federal probe into a spate of whale deaths in New Jersey and New York.

Groups from the two states wrote President Joe Biden requesting a probe of the deaths of six whales that washed ashore over the last 33 days in areas being prepared for large-scale offshore wind farms. They also are asking for a halt to site work until the causes are determined.

Cindy Zipf, executive director of New Jersey-based Clean Ocean Action, called the rate of whale deaths in the two states unprecedented.

“Is it an omen?” she asked. “Is it an alarm? Never before have we had six whales wash up in 33 days.”

She said survey boats explore the ocean floor using focused pulses of low-frequency sound in the same frequency that whales hear and communicate, which could potentially harm or disorient the animals.

The news conference was held on the beach in Atlantic City atop the buried carcass of a whale that washed ashore over the weekend in front of the Boardwalk arena that used to house the Miss America competition. The stench from the decaying animal remained powerful, even through a heavy layer of sand.

A prominent marine mammal stranding expert said that while the cause of the deaths is unknown, it could be a simple function of a larger-than-normal number of whales in the area this winter, with the number of deaths rising proportionately.

And a federal agency, the National Oceanic and Atmospheric Administration, said that to date, no humpack whale — the species accounting for most of the recent whale deaths in New Jersey and New York — has been found to have been killed due to offshore wind activities.

New Jersey is striving to be the East Coast leader in the burgeoning offshore wind energy. The state has approved three offshore wind farms and is soliciting more during the first quarter of this year. Additional projects are planned off the New York coast.

Orsted, the Danish wind power developer that will build two of those three approved projects, said its current work off the New Jersey coast does not involve using sounds or other actions that could disturb whales.

“As the world’s most sustainable energy company, we prioritize coexistence with our communities and marine wildlife,” said Maddy Urbish, the company’s head of government affairs for New Jersey. “When offshore, we combine human surveillance and state-of-the-art technical equipment to avoid any impact on marine wildlife as we build projects to advance New Jersey’s clean energy ambitions.

The groups’ demands came after a 30-foot (9-meter) humpback whale washed ashore Saturday in Atlantic City. Another young humpback whale washed up a few blocks away on Dec. 23, and a third 30-foot-long (9-meter) humpback was found on a beach in Strathmere, New Jersey on Dec. 10.

An infant sperm whale, 12 feet (3.6 meters) long, was found dead on the beach in Keansburg, New Jersey on December 5th; a 31-foot-long humpback was found dead on Indian Wells Beach in Amagansett, New York on Dec. 6th; and a 30-foot (9-meter) long sperm whale was found on New York’s Rockaway Beach on Dec. 12.

The Marine Mammal Stranding Center, located just north of Atlantic City in Brigantine, responded to the city’s two recent whale deaths. Sheila Dean, the center’s director, said it is not yet known what caused the deaths, pending post-mortem tests. But she noted that many variables could be in play, including underwater sonar use by the military, the prevalence of plastic pollution in the ocean, and the ever-present danger of collisions with ships.

She also said there is a larger-than-normal number of whales in the region right now because their food sources are still in the area. That could simply mean that with a larger total population, a corresponding number of deaths could be taking place, she hypothesized.

NOAA said it has been studying what it calls “unusual mortality events” involving 174 humpback whales along the entire U.S. East Coast since Jan. 2016. Agency spokesperson Lauren Gaches said that period pre-dates offshore wind preparation activities in the region.

About 40% showed evidence of having been struck by a ship or having become entangled in ropes, lines or fishing gear, she added.

Gaches said the agency has not authorized any “incidental” harm to marine mammals due to offshore wind activities that includes injuring or killing the animals, adding “to date, no humpback whale mortality has been attributed to offshore wind activities.”

At Monday’s news conference, the groups said offshore wind developers have applied for authorization to harass, harm or even kill as many as 157,000 marine mammals off the two states.

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