A marine researcher was missing and presumed dead Wednesday after he was attacked by a shark (search) off a popular beach near the southern Australian city of Adelaide, police said.

Two researchers from Adelaide University (search) were diving to collect cuttlefish eggs when the shark attacked. Two other people in the research team's boat saw the shark coming and managed to haul one diver to safety, but they could not prevent the second from being attacked about 1 1/4 miles off Glenelg Beach just after 4 p.m.

"One person had made it back to the boat and the other person is missing," Police Inspector Colin Cunningham said.

Police in boats scoured the sea where the attack happened and found the missing diver's oxygen tank and buoyancy vest, but they gave up the hunt for his body as night fell.

Acting Police Superintendent Jim Jeffery said it is "very doubtful that we will find the person alive."

One man managed to scramble back into the boat in time, Jeffery said, but the one who "was still underwater, he was taken."

The divers' identities were not released and there was no information available on the type of shark involved.

Bob Hill, Adelaide University's head of earth and environmental sciences, said he knew the four, and all were experienced divers.

"I'm actually quite proud of the three of them from what I have heard. ... They made every attempt they could to do the right thing," Hill said.

A local shark expert, Andrew Fox, speculated that the shark responsible likely was a great white.

"As far as determining the species of shark, it's very likely that, other than a bronze whaler shark (search), the great white shark is really the only large predatory shark that's capable of actually taking a diver," he told Australian Broadcasting Corp. radio.

The feared species is common in the cold waters off Australia's southern coast and also was blamed for a fatal attack on an 18-year-old surfer at a beach near Glenelg in December.

The last fatal shark attack in Australian waters was reported in March, when a 20-foot great white shark tore a man in half, killing him instantly as he snorkeled off the west coast.