Gulls attack whales off Argentina

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

Seagulls perched on the back of a catfish to peck. Photo: Rodrigo A. Martínez Calatalán

Thousands of southern right whales migrate to the calm waters of the Valdés peninsula off the coast of Argentina each year to mate and give birth. This 17-meter-long cetacean makes for a fascinating sight, especially with the young swimming behind. Over the past 50 years, however, the kelp gulls of the Valdés peninsula have regularly pecked any southern smooth whale that swims to the surface to breathe. They eat the skin and fat torn off the whale's back. In recent decades, the problem has become so severe that young southern catfish have died young, according to research published June 7 in the journal Biology Letters .

Although kelp gulls and many other seabirds occasionally eat fresh meat (even eyeballs) from marine mammals, research has found an increase in the number of young southern catfish that die before their first birthday. over the past few decades, as well as the frequency and severity of the injuries seagulls inflict on them. That's a sad reality, according to Macarena Agrelo, a marine ecologist at the Federal University of Santa Catarina in Brazil and co-author of the study.

Although southern cat whales and kelp gulls have long lived side by side, their relationship turned odd in the 1970s. Before that, the birds seemed content to eat the whale's skin. nature. Somehow, the seagulls realized they could get a better bite by aiming for the supply. From there, they pass on knowledge from generation to generation.

"The attack is very painful and causes extensive, deep damage, especially in the back of the young," said Mariano Sironi, scientific director at the Argentinian Whale Conservation Institute. "Although some of the incisions are quite small, in most cases the largest injuries cover a large patch of the young whale's back, which can be a meter or more in length."

Initially, gulls attack both juveniles and adults, but over time, the adult whales change their way of coming to the surface, arching their backs so that only their heads are exposed. Young whales cannot do this. The frequent attacks of kelp gulls not only inflict painful injuries on young southern whales, but also affect their ability to sleep. Combined with other stress, that causes young whales to die prematurely.

After analyzing thousands of observations and aerial photographs collected between 1970 and 2017, the team found that the number of young southern catfish injuries in the Valdés peninsula increased tenfold in the past year. two decades. During the same period, they linked the reduced survival rates of young whales to severe injuries inflicted by seagulls.

Once on the brink of extinction, southern cat whales have recovered since the ban on hunting in 1935. However, like all whale species today, the recovery is threatened by food sources. , entanglement of nets and collisions with ships. In addition, gulls also contribute to the cause.