Every year, thousands of enormous southern right whales travel to the tranquil waters of Península Valdés off the coast of Argentina to breed and give birth. These aquatic mammals, which can grow up to 56 feet in length, are a treat to watch, especially with their adorable calves in tow. However, if you happen to be around them, you might experience revulsion due to a reason that has nothing to do with seasickness.
In Peninsula Valdés, for the past 50 years, kelp gulls have mercilessly been pecking southern right whales that dare to swim to the surface for air. These birds eat the skin and blubber ripped off of the whales’ backs. Over the years, the problem has intensified, causing premature deaths of young southern right whale calves, as stated in a recent study published in the journal Biology Letters.
Though kelp gulls and other seabirds occasionally steal flesh (including eyes) from marine mammals, the study found that the number of southern right whale calves that are dying before their first year of life has increased in recent years. Furthermore, the frequency and severity of wounds that kelp gulls inflict on the calves have intensified as well.
“It’s heartbreaking to see,” stated Macarena Agrelo, a marine ecologist at the Federal University of Santa Catarina in Brazil, and one of the authors of the study.
Although southern right whales and kelp gulls have been living together for a long time, their interactions took an unusual turn in the 1970s. Prior to this, the birds seemed happy feeding on the sheets of skin that the whales shed naturally. However, they soon figured out that they could get better meals right from the source, and they have been teaching their offspring the same since then.
“The attacks are painful and result in large, deep wounds, particularly on the backs of young calves,” said Mariano Sironi, scientific director of the Instituto de Conservación de Ballenas in Argentina and co-author of the study. While some pecks are small, he said, in the most extreme cases, “the largest wounds can cover a big portion of the calves’ back and can be one meter long or even bigger.”
Initially, the gulls attacked both young calves and adults. However, over time the adults changed their way of surfacing for air by arching their backs, so that only their heads leave the water. Young whales cannot follow suit.
The constant attacks by kelp gulls cause painful injuries to young southern right whale calves, disturb their ability to rest and nurse, and combined with other stressors, cause premature deaths among the young southern right whale population.
By evaluating thousands of recorded sightings and aerial photographs taken from 1970 to 2017, the researchers found that the number of injuries sustained by young southern right whales in Península Valdés has increased tenfold in the last two decades. Over the same time frame, they linked a decrease in calf survival with the severe injuries caused to them by the birds.
“The fact that gull harassment is causing population-level impacts on these whales is pretty surprising,” Matthew Leslie, a conservation biologist at the U.S. Geological Survey who was not involved with the study, stated.
The southern right whale was once on the verge of extinction, but since the hunting of the species was prohibited globally in 1935, it has recuperated somewhat. However, like almost all whales today, the southern right whale’s recovery is threatened by declining food supplies, the regular entanglement of whales in fishing equipment, and ship strikes.
“For these whales, it’s death by a thousand cuts,” Dr. Leslie added, “and these gulls are inflicting one more.”
The study’s authors claim that humans are partially responsible for the Patagonian whales’ predicament, highlighting poorly managed landfills and the waste generated by fishing fleets as factors contributing to the increase in kelp gull populations.
“By presenting scientific evidence that gull attacks are affecting whale survival at the population level, we hope people will change their attitudes and become more involved in waste management,” Dr. Sironi explained.
