…For the past 50 years, the kelp gulls of Peninsula Valdés have been mercilessly pecking at any southern right whale that dares to swim to the surface to breathe. The birds gorge on skin and blubber ripped from the whales’ backs. Over the past few decades the problem has escalated, and is now so severe that it’s causing young southern right whale calves to die prematurely, according to a study published Wednesday in the journal Biology Letters.
While kelp gulls and other seabirds have been known to occasionally pilfer flesh (and even eyeballs) from marine mammals, the study found that the number of southern right whale calves dying before their first birthday has increased in recent decades, as has the frequency and severity of the wounds the gulls inflict upon them.
“It’s really sad to see”, said Macarena Agrelo, a marine ecologist at the Federal University of Santa Catarina in Brazil and an author of the study.
Although southern right whales and kelp gulls have long lived alongside one another, their relationship took a bizarre turn in the 1970s. Until then, the birds seemed content to feed on the sheets of skin the whales regularly shed naturally. Somehow the birds realized they could get more satisfying morsels by going straight to the source. And since then, the birds have been passing this knowledge from generation to generation.
“The attacks are very painful and cause large, deep lesions, 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 of the 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.”
At first, the gulls attacked both calves and adults, but over time the adults have changed the way they surface for air, arching their backs so that only their heads leave the water. Young whales are unable to do this.
…“The fact that gull harassment is causing population-level impacts on these whales is pretty surprising”, said Matthew Leslie, a conservation biologist with the US Geological Survey who was not involved with the study.
…The scientists behind the study argue that humans are partially to blame for the Patagonian whales’ plight, pointing to poorly managed landfills and the waste created by fishing fleets, which increase the kelp gull population.