The NG in the code name stands for National Geographic, signifying the Society's involvement as a sponsor in the project.

By mapping the crocodile's movements in this way, Botha wants to get a better picture of the creature's movements within the 1,600-hectare Flag Boshielo lake and the river that feeds into it about 125 miles (200 kilometers) north-east of South Africa's capital Pretoria.

By gaining a better understanding of the habits of the crocs in the area, he hopes to prevent development at their regular calling spots along the lake and riverbanks and so reduce the potential for conflict with humans.

Botha believes the information could also be useful in regulating crocodile numbers in closer accordance with the habitat's carrying capacity.

The leader of the project is Wouter van Hoven of the University of Pretoria's Centre for Wildlife Management. He says an important aspect of the study is to establish the reasons for the high concentration of crocodiles in that particular lake, while another lake nearby which is ostensibly equally suited and situated in a nature reserve, has no crocodiles.

"We want to see what the powers at play are-why the crocodiles seem to prefer this area and not the other," said van Hoven. "Crocodiles are not a threatened species, but we need this kind of information to take a balanced approach to nature conservation," he said.

Croc Studies Require Special Technology

GPS technology is widely used on land-based animals for studying their movements. It is fitted on a collar, and, being on land, it is fairly easy to keep track of the animal.

"With crocodiles it is far more difficult," said Botha.

"The device has to be above or just below the water surface for its signals to be received, and a large crocodile like the one we are tracking can stay deep underwater for up to two hours. Thus, you get a fix on it, and then it disappears, only to resurface much later and a considerable distance away.

"With our device, the cylinder containing the GPS and cell phone is affixed to the scales behind the head because it is normally the part of the body that is just above or below the surface. The cell phone is set to transmit readings at regular intervals. It might be that you miss a few, especially during the night when crocodiles hunt and they often go deep underwater. During the day they laze on sandbanks, making it easier to get regular readings. It is also possible to get readings between set times by sending the crocodile's cell phone a 'Where Is' message."

Catching the crocodile to fit the cylinder is a risky operation.

It is done at night from a boat, explained Botha. "We drift quietly among the crocodiles, and the one selected according to size is blinded with a strong spotlight.

"Using a long pole, a steel-cable noose is slipped over its head. The crocodile dives down, tightening the noose around its head and dislodging the cable from the pole. We let it struggle for about five minutes to tire sufficiently for us to drag it onto the shore.

"The first priority is to get its head under control and to tie its jaws shut with duct tape. We also tie the feet. It takes at least four people to do the job. The important thing is not to get head-butted or hit by its tail, especially when it is pulled from the water. We don't use tranquilizer. We don't want to risk the crocodile getting attacked by others while recovering from sedation.

"Four holes are drilled into the bony scales behind the head and surgical-steel wire is used to attach the cylinder. It takes about ten minutes to complete the operation and for the crocodile to be set free again," said Botha.

Martin Haupt of African Wildlife Tracking, supplier of the tracking device, explained that both the GPS and cell phone operate from a 3.6-volt lithium battery which will give five readings a day for two years. To save power, the GPS/GSM unit only switches on when sending and receiving information at set times. Settings can be adjusted via the scientist's PC or cell phone.

The unit also has an on-board logger that can store 2,000 position readings. Therefore no readings are lost while the crocodile is out of GSM range.

The tracking project is part of a wider research program at the Flag Boshielo lake which has also involved National Geographic Television host Brady Barr. With Botha's assistance, Barr got really close to crocodiles by using several innovative gadgets. He did this for the National Geographic Television series Reptile Wild and Croc Chronicles.

Botha said one gadget Barr used was a foam-rubber crocodile mask which he put over his head. "It looked so much like the real thing that one big crocodile saw it as competition and threatened to attack it. We had to get Brady very quickly out of the water."

They also tried a remote-controlled boat with a camera mounted, but it was not too successful. For some reason it scared off the crocodiles.

The worst fate suffered, said Botha, was last year by a small remote-controlled vehicle placed on a sandbank where the crocodiles like to lurk. It was not long before a big crocodile burst from the water and caught it between its jaws. "You just saw wheels flying. I found the broken camera two months later in the mud when the lake had gone down somewhat."