JOHANNESBURG – Chimpanzees at a sanctuary founded by famed primatologist Jane Goodall pulled a Texas graduate student into their fenced-off enclosure, dragging him nearly a half-mile and biting his ear and hands.

Andrew F. Oberle was giving a lecture to a group of tourists at the Chimp Eden sanctuary on Thursday when two chimpanzees grabbed his feet and pulled him under a fence into their enclosure, said Jeffrey Wicks of the Netcare911 emergency services company.

The 26-year-old anthropology student at the University of Texas at San Antonio, suffered “multiple and severe bite wounds,” Wicks said.

He was in critical condition Friday after undergoing surgery at the Mediclinic hospital in Nelspruit, 180 miles (300 kilometers) from Johannesburg, hospital officials said.

Oberle, who was doing research at the sanctuary, had crossed the first of two fences separating the chimpanzees from visitors and was standing close to the second fence, which is electrified, at the time of the attack, said Edwin Jay, chairman of the Jane Goodall Institute South Africa.

The sanctuary was temporarily closed after the attack, said David Oosthuizen, the institute’s executive director.

“The safety of our visitors and staff is paramount,” Oosthuizen said. “We have never had an incident like this, and we have closed the sanctuary to investigate how we can ensure it will not happen again.”

Oberle lost part of an ear and parts of his fingers in the attack, according to the South African newspaper Beeld. It said the sanctuary’s manager, Eugene Cussons, fired into the air to scare the chimps away from Oberle, then chased them back into their enclosure. Cussons is the host of Animal Planet’s “Escape to Chimp Eden.”

The two chimpanzees were placed in their night enclosure after the attack and will be held there pending the investigation, after which they would be returned to their enclosure, Jay said.

Steve Ross, an ape expert at Chicago’s Lincoln Park Zoo, said chimpanzees are “naturally a fairly violent species, naturally aggressive, very interested in things like power and hierarchy.”

Even researchers who understand their power, “sometimes just relax a little bit,” Ross said. “And you can never relax with these chimps. They are so unbelievably fast, strong, and they’re always looking for an opportunity.”