PENINSULA VALDES, Argentina: Scientists in Argentina are investigating why an unusually large number of southern right whale calves are dying and washing ashore along the Patagonian coast.

Dozens of dead calves have been found around Peninsula Valdes in Chubut province, one of the world's main breeding areas for southern right whales. The whales were hunted almost to extinction during the 19th and 20th centuries, but their numbers have recovered, and they now return to the peninsula's protected waters to give birth and raise their young.

"We're looking into the whale calf deaths based on 23 years of monitoring that we have of this same population. That's what allows us to say that this is an unusual event," said Marcela Uhart, a veterinarian with the One Health Institute at the University of California, Davis. She is leading the investigation through the Southern Right Whale Health Monitoring Program.

Researchers believe the leading explanation could be infections caused by marine bacteria. The bacteria may enter the calves' bodies through wounds caused by kelp gulls, Uhart said.

For decades, kelp gulls have attacked whales as they surface to breathe. The birds peck at their skin and feed on their blubber.

Adult whales have learned to protect themselves by surfacing with only their heads above the water, keeping their backs below the surface and away from the gulls. Young calves cannot do the same, leaving them more exposed to attacks.

Dead calves have been washing ashore near the Gulf city of Puerto Madryn, including areas close to the main waterfront. The deaths have worried local residents and tourists.

Residents have reported seeing hundreds of carcasses, but researchers have not given a final death count. They said the full number would only become clear after the whale season ends, around late November.

Uhart and a team of biologists, veterinarians, and park rangers are searching the coast for dead calves using boats, aircraft, and drones.

The investigation involves examining and photographing the carcasses before they decompose. Researchers are collecting skin and organ samples and sending them to a veterinary school in Tandil, a city farther north, for testing.

Researchers have already found bacteria in some tissue samples. However, scientists are still growing the samples in laboratories to identify the bacteria and determine whether infections caused the deaths.

Even if bacteria are confirmed as the cause, researchers still need to understand why they appear to have become more dangerous this year.

Scientists are examining whether changes in marine conditions played a role. Warmer sea temperatures, possibly linked to climate change or El Niño, could have weakened the calves' ability to fight infections.

Uhart said the researchers were examining whether these factors had created conditions that allowed bacteria to overcome the young whales' immune systems and cause widespread deaths.

The investigation will also look at whether human activity played a role. Uhart said researchers wanted to identify the factors behind the unusual deaths and prevent the whales from facing a similar threat again.

"If the cause relates to something that we are doing as humans, then we need to change that," Uhart said. "We don't want to endanger these whales again."