Waves are washing dozens of dead southern right whale calves ashore around the Valdes Peninsula in Chubut Province, sparking an urgent scientific race to identify the cause of mortality.
Investigators in Argentina are confronting an unusual spike in young whale mortality as researchers examine a prevailing hypothesis involving bacterial infections spread by kelp gulls. While local residents have reported finding hundreds of carcasses, researchers are withholding a precise death toll until the current season concludes around late November.
Protected Waters of Chubut Province Become a Site of Alarm
The Valdes Peninsula serves as a primary breeding ground for Southern right whales, a population that rebounded after being hunted to the brink of extinction during the 19th and 20th centuries. Today, the animals gather in the protected waters of the peninsula to give birth and nurse their young. However, the discovery of dead calves near the coastal city of Puerto Madryn and surrounding waterfront areas has raised alarm among local residents and tourists.
Decades of Monitoring Reveal an Exceptional Mortality Event
We are studying calf mortality cases based on monitoring data collected over 23 years for this specific group; and this is what allows us to say that this event is unusual.
Marcela Uhart, veterinarian at the One Health Institute at the University of California, Davis
Air, Sea and Land Surveys Targeting Rapid Decomposition
Uhart and an interdisciplinary team of biologists, veterinarians, and wildlife reserve rangers are surveying the coastline using beaches, boats, planes, and drones. The field work requires documenting and examining carcasses rapidly before decomposition sets in, allowing teams to harvest skin and organ samples for laboratory analysis at a veterinary college further north in Tandil.
Kelp Gulls Prey on Vulnerable Whale Calves
The leading hypothesis points to a marine bacterium entering the animals through wounds inflicted by kelp gulls. For decades, these gulls have preyed upon whales that surface to breathe, feeding aggressively on their skin and blubber. While adult whales have learned to surface by exposing only their heads while keeping their vulnerable backs submerged, young calves cannot perform this defensive maneuver.
Although laboratory testing has already detected bacteria in the collected tissue samples, researchers are still working to culture the samples to identify the exact microbes and confirm whether the infection caused the deaths. Even if the bacteria are confirmed as the direct cause, scientists must still determine why the pathogen has turned exceptionally lethal this year.
