Patagonian Coast Whale Mortality Investigation
Investigators in Argentina are racing against decomposition to solve the mystery of baby southern right whales washing up dead in unusually high numbers along the country’s Patagonian coast. Scores of calf carcasses have washed ashore around Península Valdés in Chubut province, a major breeding ground for the species, with researchers pointing to a potential combination of gull attacks and bacterial infections.
“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, who leads the investigation as head of the Southern Right Whale Health Monitoring Program.
Kelp gulls leave calves vulnerable to bacterial infections
The leading hypothesis points to marine bacteria entering the calves’ bodies through skin injuries inflicted by kelp gulls. For decades, these seabirds have pecked at whales surfacing to breathe, feeding on their skin and blubber. While adult whales have learned to surface with only their heads exposed to keep their backs underwater, young calves cannot perform this defensive maneuver, leaving them vulnerable to attacks.
Uhart and a team of biologists, veterinarians, and park rangers have been surveying the dead calves from shore, boats, planes, and drones around the gulf city of Puerto Madryn. The fieldwork requires examining the carcasses and collecting skin and organ samples for testing at a veterinary school in Tandil. While bacteria have been detected in those tissue samples, researchers are still culturing the microbes to confirm whether infection caused the deaths.
Warming sea temperatures may overwhelm whale immune systems
Researchers are also investigating why these bacterial infections have become so lethal during the current breeding season. Changing marine conditions, including warming sea temperatures potentially linked to climate change or El Niño, may create what Uhart describes as a “perfect storm” that overwhelms the immune systems of the babies.
Although southern right whales have gradually rebounded since receiving international protection in 1935—following hunting in the 19th and 20th centuries that nearly drove them to extinction—their recovery remains vulnerable. The species faces ongoing global pressures, including declining food supplies, fishing gear entanglements, oil spills, and ship strikes, meaning that calf losses on the current scale could slow the population’s recovery.
Researchers collect samples to determine whale calf death toll
When will researchers know the exact death toll for the whale calves?
Researchers declined to provide a final death toll while the monitoring work is underway, stating that the total number of dead calves will become clear after the season ends around late November.
Where are the biological samples being tested?
Park rangers, veterinarians, and biologists are collecting skin and organ samples from the carcasses around Puerto Madryn and transporting them north for laboratory testing at a veterinary school in the city of Tandil.
Why are adult southern right whales able to avoid gull attacks while calves cannot?
Adult whales protect themselves by surfacing with only their heads exposed and keeping their backs underwater out of reach of the birds, a maneuver that calves cannot do.