GFor some time now, large seagulls have been targeting whales off an Argentine peninsula. A research team reports in the journal that this has dire consequences for marine mammals BiologyLetters. Above all calves are increasingly weakened by the injuries, their survival rate is dwindling. The unusual seagull behavior is now threatening the population of the affected region.
Kelp gulls (Larus dominicanus) are among the largest gull species in the world with a body length of over 50 centimeters and a wingspan of over one meter. They eat limpets and waste, but also prey on fish, smaller mammals and birds.
But off Argentina’s Valdés peninsula, the birds have been using certain ones for around three decades whales as a source of food: They land on southern right whales swimming above and tear out pieces of skin and fat from them. In the meantime, mothers with boys in particular are being attacked, write the behavioral researchers. But there on the coasts of Argentina, Brazil and Uruguay the southern right whales, also called southern right whales (Eubalaena australis), raise their calves.
theirs through seagulls The number of wounds caused has increased significantly since the mid-1990s, as reported by Macarena Agrelo’s team from the Universidade Federal de Santa Catarina in Florianópolis. Since 2003, an unusually high calf mortality rate has been recorded locally. It is assumed that the seagull attacks are the cause, especially since the birds prefer to aim at animals that are already injured.
It has already been observed that the whales come up to breathe less often and swim faster because of the constant threat. Overall, around a quarter of the daylight hours are now used to flee from the seagulls, explains Agrelo’s team. This increases the energy requirements of the animals, while at the same time the calves are breastfed less. Blood tests on dead animals would have revealed elevated levels of stress hormones.
The scientists now analyzed for almost 600 whales that had been photographed in the area from 1974 in their year of birth and later re-photographs between 1974 and 2017. Some years were excluded due to lack of data. According to the evaluation, fewer and fewer calves survived their first year of life – at least there were no new pictures of them. At the same time, the severity of the wounds inflicted by the seagulls increased.
Southern right whales raise their calves off the coasts of Argentina, Brazil and Uruguay
Source: Nicolas Lewin, Instituto de Conservación de Ballenas
From the nursery in front of Valdés, the mother whales migrate with their calves to distant summer feeding grounds. Agrelo’s team explains that if the young animals are in poor health as a result of the wounds inflicted, their chances of surviving this strenuous journey are likely to decrease.
Another possible explanation for the fact that an increasing proportion of the calves were not photographed off the peninsula again could be that the animals did not return there, but increasingly migrated to other coastal regions, the researchers point out. An extension of the photo documentation to other areas should help to clarify this possible influencing factor.
The team sees a sensible measure in the region to curb the availability of waste and other man-made food sources for the large seagulls.
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