Birds with a taste for meat threaten whale calves

Thousands of colossal southern right whales travel each year to the calm waters of the Pennsula Valds off the coast of Argentina to breed and give birth. The cetaceans, which can reach 56 feet in length, are a sight to behold, especially with their young in tow. But if you venture to see them, sometimes you may feel your stomach turn for a reason that has nothing to do with seasickness.

For the past 50 years, the kelp gulls of the Valds Peninsula have mercilessly pecked at any southern right whale that dares to swim to the surface for air. Birds gorge themselves on the skin and blubber ripped off the backs of whales. The problem has worsened in recent decades and is now so severe that it is causing the premature deaths of young southern right whale pups, according to a study published Wednesday in the journal Biology Letters.

While kelp gulls and other seabirds are known to occasionally steal the meat (and even eyeballs) from marine mammals, the study found that the number of southern right whale calves that die before their first birthday has increased in recent years. decades, as well as the frequency and severity of injuries seagulls inflict on 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 next to each other, their relationship took a bizarre turn in the 1970s. Up until then, the birds seemed content to feed on the skin sheets that whales regularly shed naturally. Somehow the birds realized they could get more satisfying tidbits by going straight to the source. And since then, birds have passed on this knowledge from generation to generation.

The attacks are very painful and cause large and deep lesions, particularly on the backs of young calves, said Mariano Sironi, scientific director of the Instituto de Conservacin de Ballenas in Argentina and co-author of the study. While some of the beaks are small, he said, in the most extreme cases, the largest wounds can cover a large portion of the calves and can be three feet long or even larger.

At first, gulls attacked both hatchlings 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 constant attacks by seaweed gulls not only cause painful wounds to young southern right whale calves, but also interfere with their ability to rest and nurse. This, combined with other stressors, is causing young southern right whales to die prematurely.

After analyzing thousands of documented sightings and aerial photographs collected from 1970 to 2017, the researchers found that the number of injuries sustained by juvenile southern right whales in the Pennsula Valds has increased nearly tenfold over the past two decades. Over the same period, they linked a decrease in calf survival with severe injuries inflicted by birds.

The fact that seagull harassment is causing population-level impacts on these whales is pretty surprising, said Matthew Leslie, a conservation biologist at the US Geological Survey who was not involved in the study.

Once on the brink of extinction, the southern right whale has recovered since hunting was banned in 1935. However, as with nearly all whales today, that recovery is threatened by declining food sources, snags in fishing gear and ship strikes.

For these whales, its dead from 1,000 cuts, Dr. Leslie said, and these gulls are adding another cut.

The scientists behind the study argue that humans are partly to blame for the plight of Patagonian whales, pointing to poorly managed landfills and waste created by fishing fleets, which boost the kelp population.

By providing scientific evidence that seagull attacks impact whale survival, we hope people can change their minds and become more involved in improving waste management, said Dr. Sironi.

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