PORT ELIZABETH, South Africa, April 14 (UPI) -- The African elephant still is endangered across most of the continent, but conservation efforts in South Africa have been so successful game reserves there soon may be faced with killing thousands of the animals to keep the herds from overpopulating.

Although the African elephant population numbered 5 million to 10 million in 1930, there now are less than 500,000 of the animals. South Africa, however, has seen rapid increases in recent years in the elephant herds found throughout the country on more than 20 national parks and private reserves.

The populations are growing so large Addo Elephant National Park is expanding and private game reserves are using contraceptive vaccines to keep their populations from growing beyond capacity.

The vaccine has drawbacks, however, and can be difficult, if not impossible, to administer in larger herds so the populations may keep growing until the reserves are forced to slaughter thousands of the animals.

"It's inevitable that large parks will have to cull thousands," Johan Joubert, director of wildlife at Shamwari Game Reserve, located just north of Port Elizabeth, told United Press International.

The reason is that overcrowding leads to increased aggression as well as destruction of habitat.

"We're seeing a disaster in countries like Botswana," where overpopulation led to elephants destroying vegetation that can take hundreds of years to regenerate, Joubert said.

Anban Padayachee, senior section ranger at nearby Addo National Elephant Park, said he sees the same thing among his elephant population.

"We're seeing aggressive levels rising merely due to overcrowding," Padayachee said. The animals also are devastating swatches of land, he added.

Currently, killing elephants in South Africa is banned because of international pressures but Joubert and Padayachee said it would be wise to reverse the ban because if the growing elephant population is not addressed soon, the reserves will have to kill even more animals.

"Culling is the saddest thing because you can't cull just one elephant, you have to cull the whole family," said Conrad Ensliw, a game ranger at Shamwari.

The reason is elephants are very social animals with close-knit family structures, Joubert said. They will mourn and nurse their dead, so it is easier on the herds to take out an entire family unit rather than an individual, he said. "It's quite sad to do it," he added.

A contraceptive vaccine exists but requires two doses given two weeks apart. This means animals must be identified and relocated to ensure the second dose is given to the same elephant, Joubert said. This can be an effective strategy in the smaller herds but for larger herds it is nearly impossible to accurately identify individual elephants and track them so they can be located for a second dose.

The vaccine, therefore, probably will not be a useful tool for keeping the populations in check, he said.

Padayachee said the vaccine also causes increased aggression among males toward the females because the bulls get frustrated their repeated mating efforts are unsuccessful.

He said there should be a governing body that private reserves could approach to get approval to cull select numbers of elephants. That might help change public perception that culling is something to be avoided at all costs, he added.

He said when Kruger National Park recently was forced to cull some of its elephants, every part of the animal, from the tusks to the hide, was utilized, so it was not a wasteful act and helped the existing herds in the long-run.

In addition, there are so many elephants now the gene pool is large enough that culling is not a threat to the conservation of the species, he said.

Steve Mitchell is UPI's Medical Correspondent.
He has been on assignment in South Africa.
E-mail sciencemail@upi.com