Argentine Researchers Investigate Unusual Mortality of Southern Right Whale Calves

PENINSULA VALDES, Argentina — Argentine investigators are unraveling the mystery of unusually high numbers of dead whale calves washing ashore along Patagonia’s coast.

Scores of calf carcasses have washed ashore along Peninsula Valdes, a key breeding ground for southern right whales in Argentina’s Chubut province. Once hunted to the brink of extinction during the 19th and 20th centuries, these whales now return to the peninsula’s sheltered waters to give birth and nurse their young.

“We are investigating a significant die-off of whale calves based on 23 years of monitoring this population, which designates this as an unusual event,” said Marcela Uhart, veterinarian with the One Health Institute at the University of California, Davis, and head of the Southern Right Whale Health Monitoring Program.

The prevailing hypothesis is that whale calves are succumbing to marine bacterial infections entering through injuries inflicted by kelp gulls, Uhart noted.

For decades, kelp gulls have pecked at whales surfacing to breathe, consuming their skin and blubber. Adult whales learn to surface with only their heads exposed, keeping their backs submerged and out of reach. Calves are unable to perform this maneuver, leaving them vulnerable to attack.

Carcasses have been washing ashore near Puerto Madryn, a gulf city, and along the central waterfront, alarming residents and tourists. While locals have reported hundreds of carcasses, researchers have declined to provide a death toll, noting that final figures will become clear after the season ends in late November.

Uhart and a team of biologists, veterinarians, and park rangers have been conducting searches for deceased calves via shore surveys, boats, aircraft, and drones.

The necropsy work is demanding: researchers photograph and examine carcasses, racing against decomposition to collect skin and organ samples for testing at a veterinary school in Tandil, north of the study area. Bacteria have been detected in the tissues, though researchers are still culturing samples to identify the specific microbes and determine whether infection caused the deaths, Uhart said.

Even if bacteria are confirmed as the cause, researchers must still determine why these infections have proven so lethal this year.

Shifts in marine conditions, such as warming sea temperatures potentially linked to climate change or El Niño, may contribute to a ‘perfect storm’ in which bacterial pathogens overcome calf immunity and cause mortality, Uhart said. ‘To the extent possible, we will identify the triggering factors driving this unprecedented event.’

The International Whaling Commission notes that right whales derive their name from whalers, who deemed them the ‘right’ targets to hunt due to their slow swimming, coastal proximity, and tendency to float when killed.

Although illegal hunting persisted into the 1970s, southern right whales have gradually recovered since gaining international protection in 1935. However, their recovery remains threatened by widespread pressures: declining food supplies, fishing-gear entanglements, oil spills, and ship strikes.

“If the cause is linked to human activity, we must change course,” Uhart cautioned. ‘We must not endanger these whales again.’

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