Humpback whales (Megaptera novaeangliae) can reach 18 meters in length and weigh 40 tons. They are colossal animals capable of pushing out of the water with their powerful tail, or simply swim some 25,000 kilometers a year. Adults are famous for singing for hours with a complex mix of howls, roars and whistles, which are believed to play a role in reproduction.
The «small» cubs of yubarta live in a different world. When they are born they are only five meters, and they have to spend a whole year with their mothers to receive care and milk. They swim in a world where males who want to breed with their mothers can be a threat, and where, in the midst of darkness, the fearsome orcas stalk. They can hear the whales’ chants and also emit beeps that travel quickly through the water and function as a natural sonar that reveals the position and size of their prey. Among them are the small cubs of Yubarta.
A study published Wednesday in the journal Functional Ecology has discovered a strategy that mother and child use to survive in the middle of the ocean. The offspring need to keep in touch with their moms and sometimes they have to ask for milk to suckle. When they communicate, they do so by whispering, to prevent hunters from hearing them.
«Orcas (killer whales) hunt Yubart hatchlings at the exit of the Gulf of Exmouth, northwest of Australia, so with whispers, whales make it difficult to be detected by killer whales or attract males they want Reproduced with females, «explained Simone Videsen, the study’s first author and researcher at the University of Aarhus (Denmark).
As researchers from Denmark and Australia found, the youngsters spend a lot of time resting and sucking. The little ones communicate with their mothers using intimate roars and squeaks, very different from the stenting singing of the males.
Scientists used sensors designed at the University of St Andrews in Australia to capture the sounds of whales. 48 hours after adhering through a suction cup to the Yubartas, these devices were released from the animals and collected by the researchers.
Roces to ask to nurse
As a result, they found that most of the communication between mother and offspring occurred when they were swimming to stay together in the murky waters of the Gulf of Exmouth. «We also hear a lot of friction sounds, like when two balloons rub against each other, which we think is a way for the baby to tell his mother he wants to suckle,» Videsen said.
In the opinion of the authors, the advances make clear the importance of maintaining the silence in the breeding water of these yubartas if this species is to be conserved. «We have found that mothers and offspring are probably sensitive to boat noise. The noise of the propellers could mask their calls. »
The difficult beginnings of the Yubartas
«We hardly know anything about the early stages of life of whales in the wild, but we know that they are crucial for the survival of the young during their long migrations to the feeding grounds,» Videsen explained. Hence the importance for conservation to focus on breeding these beautiful animals.
The beginning of the life of the Yubartas is very difficult. Together with the threat of killer whales, the offspring have to be able to leave behind their breeding grounds and swim some 8,000 kilometers in stormy seas with strong winds to reach areas rich in food.
Yubartas spend the summer in the food-bearing waters (krill and small fish) of the Arctic and Antarctic, and in winter they migrate to the tropics to reproduce and give birth. While in tropical waters, such as the Gulf of Exmouth, the offspring should gain as much weight as possible before embarking on their first migration into the polar waters. During the first weeks of life, they can grow up to one meter each month.