Unusual number of right whale calves die off Argentina's coast

The brief in 4 cards

1. Context1 / 4
   • Scores of southern right whale calf carcasses have washed ashore around Península Valdés, in Argentina's Chubut province, during the current calving season.
   • Scientists of the Southern Right Whale Health Monitoring Program, drawing on 23 years of watching this population, describe it as an unusual event.
   • The leading hypothesis is bacterial infection, possibly entering through wounds made by kelp gulls. Bacteria have been found in tissues, but samples are still being cultured to confirm the cause of death.
   • Researchers are also examining whether warming sea temperatures, possibly linked to climate change or El Niño, weakened the calves' resistance.
2. Key highlights2 / 4
   • The place. Península Valdés is a UNESCO World Heritage Site and one of the main calving and nursing grounds of the species. Most calves there are born around August, and mother-calf pairs stay about three months before migrating to the feeding grounds.
   • The gull problem. Since the 1970s, kelp gulls at Península Valdés have learned to peck skin and blubber from the backs of living whales. The attacks have increased over the decades, and mother-calf pairs are the main targets. The behaviour is almost unknown in other whale populations.
   • Why calves suffer most. Adult whales can arch their backs to keep the gulls off, but calves cannot, which leaves them open to repeated wounds.
   • A recurring pattern. At least 626 calves died at Península Valdés between 2003 and 2014. Earlier investigations looked at gull harassment, harmful algal blooms and other factors, without settling on a single cause.

   The table below shows the three right whale species and their status on the IUCN Red List.

   Species	Range	IUCN Red List status
   Southern right whale (Eubalaena australis)	Southern Hemisphere	Least Concern
   North Atlantic right whale (Eubalaena glacialis)	North Atlantic	Endangered
   North Pacific right whale (Eubalaena japonica)	North Pacific	Endangered

3. Key concepts3 / 4

   1. What is a baleen whale?

   A whale that has plates of baleen instead of teeth, which it uses to filter small prey such as krill and copepods from seawater. Right whales, blue whales and humpbacks are all baleen whales.

   2. Why "right" whale?

   Whalers thought them the "right" whales to hunt: they swim slowly, stay near the coast and float once killed. That made them among the first species hunted almost to extinction. International protection has let the southern species recover, though some populations, such as the Chile-Peru group, remain very small.

   3. What is marine disease ecology?

   The study of how pathogens, environmental conditions and host animals interact. A pathogen may be harmless in a healthy calf but fatal in one already weakened by wounds, poor feeding or unusual water temperatures. Scientists call such a combination a "perfect storm".

   4. What is a bioindicator species?

   A species whose health reflects the state of its ecosystem. Large, long-lived whales that feed across wide stretches of ocean can signal changes in food supply, pollution and disease.

4. Way forward4 / 4

   These are suggested measures, not approved policy.

   • Strengthen disease surveillance through systematic necropsies and long-term health monitoring of whale populations.
   • Study the gull problem, including whether the waste and fishery discards that sustain large gull populations can be reduced.
   • Track ocean conditions such as sea temperature and algal blooms alongside mortality data.
   • Reduce human pressures that add stress: entanglement in fishing gear, ship strikes and disturbance of habitat.

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