Whale shark expert Dr. Brent Stewart attaches a radio-frequency identification tag to a whale shark in Indonesia. (Mark Erdmann)

Scientists studying whale sharks in Indonesia have devised a way to track the hulking giants that is both more affordable and more reliable than satellite tracking: They’re using the kind of radio-frequency identification tags that many Americans put on their pets.

Tags that transmit data to satellites cost hundreds of dollars and can get lost after detaching, often within a matter of months. But embedded radio-frequency tags cost just a few dollars and can be expected to last for the life of the animal.

Late last month, researchers from Conservation International, WWF-Indonesia, Hubbs SeaWorld Research Institute of San Diego and the State University of Papua inserted RFID tags on 30 whale sharks in Indonesia’s Cenderawasih Bay National Park, where they have been gathering in recent years to feed on silverside baitfish.

Mark Erdmann, senior adviser to CI-Indonesia’s marine program, said in an interview that the tiny tags had “never been used on big, free-roaming animals in the ocean” because they can be read only by a receiver wand waved near a tagged animal.

But Brent Stewart, senior research scientist at Hubbs, suggested doing it because the sharks routinely return to the same place to feed.

Researchers have long assumed that whale sharks — the biggest fish in the world, measuring as large as a school bus — primarily feed on plankton. But last month Erdmann videotaped them gorging on silverside baitfish caught in lift nets attached to a fishing platform.

The sharks “have become a little too friendly with the nets,” he noted, saying he had helped disentangle a trapped shark. Nevertheless, the researchers are taking advantage of the allure of the fish-filled nets to further shark research.

The group used two ways to embed the pill-size radio-frequency tags in 30 sharks, 29 of which were adolescent males. For one method, divers use a pole spear to penetrate the shark’s thick layer of blubber; for the other, a large-bore syringe. “That one proved to be much more difficult with the animals because they tend to feel it a little more, and they tend to rapidly knock you off,” Erdmann said.

While Cenderawasih Bay National Park has enjoyed government protection for nearly two decades, the aggregation of whale sharks has become so popular with the public that Indonesia decided this month to make them a nationally protected species. The move is significant because Indonesia ranks as the world’s largest exporter of shark, valued for shark fin soup.

“Whale sharks are just fantastic ambassadors for all sharks,” said Greg Stone, Conservation International’s chief scientist for oceans. “These don’t hurt anybody. . . . They’re an entry point for helping people understand the importance of sharks in the world.”