Seagulls attack whales off Argentina

Kelp gulls often target the backs of southern right whales, threatening the endangered species' ability to recover.

Seagulls perch on the back of a right whale to peck. Photo: Rodrigo A. Martínez Calatalán — Seagulls perch on the back of a right whale to peck. Photo: *Rodrigo A. Martínez Calatalán*

Thousands of southern right whales migrate to the calm waters of the Valdés Peninsula off Argentina each year to mate and give birth. The 55-foot-long (17-meter) marine mammals make for a fascinating sight, especially when their calves swim along. But for the past 50 years, kelp gulls in the Valdés Peninsula have been pecking at any southern right whales that come to the surface to breathe, eating the skin and blubber that rips off the whales’ backs. In recent decades, the problem has gotten so bad that it’s been killing juvenile southern right whales, according to a study published June 7 in the journal Biology Letters .

Although kelp gulls and many other seabirds occasionally eat fresh meat (and even eyeballs) from marine mammals, research has found that the number of southern right whale calves dying before their first birthday has increased over the past few decades, as has the frequency and severity of the injuries the gulls inflict on them. That’s a sad reality, says study co-author Macarena Agrelo, a marine ecologist at the Federal University of Santa Catarina in Brazil.

Though southern right whales and kelp gulls have long coexisted, their relationship became strange in the 1970s. Until then, the birds seemed content to eat the flaked whale skins in the wild. Somehow, the gulls figured out they could get a better bite by targeting the supply. They’ve since passed the knowledge down from generation to generation.

“The attack is very painful and causes extensive, deep damage, especially to the calf’s back,” said Mariano Sironi, scientific director at the Argentine Whale Conservation Institute. “Although some of the punctures are quite small, in most cases the largest wounds cover a large area of the calf’s back, which can be a meter or more long.”

Initially, kelp gulls attacked both calves and adults, but over time, the adults changed their way of surfacing, arching their backs so that only their heads were exposed. Calves cannot do this. The frequent attacks by kelp gulls not only left the southern right whale calves with painful wounds, but also affected their ability to sleep. Combined with other stresses, this led to early deaths.

After analyzing thousands of observations and aerial photographs collected between 1970 and 2017, the team found that injuries to juvenile southern right whales in the Valdés Peninsula increased tenfold over two decades. During the same period, they linked the reduced survival rate of calves to severe injuries caused by seagulls.

Once on the brink of extinction, the southern right whale has recovered since a hunting ban was imposed in 1935. However, like all whales today, its recovery is threatened by predation, entanglement in nets, and ship strikes. Gulls also play a role.

An Khang (According to NY Times )

Source link