After nearly 100 years since they were last spotted, the world's third-largest whales have reappeared off the coast of Argentina.
The giant blue-grey creatures were once on the brink of extinction due to relentless hunting in the 1920s and 1930s.
Whaling ships operating along and beyond Argentina's shores severely depleted the sei whale population, causing their disappearance from the region.
Due to global bans on commercial whaling enforced in recent decades, sei whales are returning to their former waters.
"They did not become extinct but were so reduced that no one saw them," said Mariano Coscarella, a biologist and marine ecosystem researcher at Argentina's CONICET scientific agency, according to NDTV World.
Adding that "after nearly a century of being hunted to near extinction, sei whale populations are now bouncing back and returning to their former habitats,"
It has taken decades for sei whale numbers to rebound sufficiently for sightings to occur again-in this case, 80 years.
Sei whales, who belong to the Baleen whale family, are known for their distinctively tall, curved dorsal fins and relatively small, pointed flippers.
They can reach lengths of up to 62-66 feet and weigh between 28 and 45 metric tons.
Argentina's CONICET team recently fitted some sei whales with satellite trackers to monitor their migration patterns, gathering valuable footage of the whales in action via drones and underwater recordings, reported NDTV World.
Coscarella said this was "a success of conservation on a global scale," attributing the recovery to the worldwide ban on whaling.
