By air and by sea, the Coast Guard was on the lookout Tuesday for sharks off North Carolina's Cape Hatteras National Seashore after a man was killed and his girlfriend was critically wounded while swimming Monday.

National Park Service spokeswoman Mary Doll said three types of sharks — sand tiger, bull and scalloped hammerhead — are common in the area along the Outer Banks.

Beaches were open Tuesday but officials advised swimmers to be cautious, especially near dusk and dawn, when sharks look for food near the shore.

The Labor Day attack, the first fatal one off North Carolina's coast in more than 40 years, came less than two days after a 10-year-old boy was killed by a shark near Virginia Beach, about 135 miles to the north.

Doll identified the dead man as Sergei Zaloukaev, 28, and Natalia Slobodskaya, 23. The Russian nationals lived together in Oakton, Va., a suburb of Washington, according to neighbors.

A medical examiner determined that Zaloukaev died of massive blood loss caused by multiple shark bites, Doll said.

Slobodskaya was alert and stable but remained in critical condition Tuesday, said Sandra Miller, spokeswoman for Sentara Norfolk General Hospital in Virginia. She was on a ventilator to assist her breathing, said Dr. Jeffrey Riblet, a trauma surgeon at the hospital.

Zaloukaev and Slobodskaya were swimming close to shore Monday afternoon at Avon, N.C., when a shark struck. 

Witness Gary Harkin, 33, of Columbus, Ohio, said Zaloukaev made it back to shore, still conscious but badly mauled. 

"He was still talking when he came out of the water," Harkin told The Virginian-Pilot of Hampton Roads, Va. 

Harkin tried using his t-shirt as a tourniquet on the Zaloukaev's leg, which had been partially bitten off, while his friend Carolyn Richards attempted CPR. 

"I did have a pulse on him twice, but I lost him," Richards said. 

Doll said that when the first official, a Dare County sheriff's deputy, arrived, Zaloukaev was in full cardiac arrest. 

Slobodskaya had lost her left foot and was severely bitten on her left hip, as well as in the groin area, Harkin said. She was airlifted to the Sentara Norfolk General Hospital in Virginia, where she underwent surgery and was in the trauma intensive care unit Tuesday morning. 

About 135 miles up the coast at Virginia Beach, Va., the beaches remained open despite the death Saturday of 10-year-old David J. Peltier, who was attacked by a shark while surfing with his father and two brothers. 

The shark bit into Peltier's left thigh while the boy swam in only 4 feet of water, and would not release its grip until Richard Peltier, David's father, struck the shark several times on the head. The boy was rushed to a Norfolk, Va., hospital, but had lost too much blood and died after about 10 hours. 

"I just wonder why it had to be him," the boy's mother, Carol Miles, 29, told the Richmond Times-Dispatch. "He did not deserve this, but he's in good hands now. The Lord wanted an angel, and he got one." 

The attacks on the Russian couple were the first reported shark incident in North Carolina waters since 1957, according to the International Shark Attack File in Gainesville, Fla. 

Avon residents and swimmers were stunned by the attack. 

"My son fishes and surfs these waters all the time," said Carlene Beckham, an employee of the Avon Fishing Pier. "But after seeing what happened today he said he's not so sure anymore." 

Park officials in Avon decided not to close the beach, but said they would fly over the water Tuesday searching for sharks or any unusual activity. 

Despite a summer of widely reported shark attacks, the deaths of the boy and the Russian man were the first U.S. fatalities in over a year. A Florida man was killed in 2000 while swimming near his home in St. Petersburg Beach. 

Shark attacks were thrust into the spotlight in early July when 8-year-old Jessie Arbogast had his right arm ripped off by a 6½-foot-long bull shark off Florida's Gulf Coast. His arm was reattached after a daring rescue by his uncle, and he remains in a light coma. 

The Associated Press contributed to this report