Global Warming Puts Southern Ocean Whales On A Diet – ScienceDaily


In June, when winter bites in the Southern Hemisphere and the sea around the South Pole freezes over, right whales swim north. Many of them congregate in the bay outside the South African town of Hermanus.

Here, South Africa’s warmer waters are ideal for mating or raising newborn calves. However, there is no food for the whales, and throughout the winter, right whale mothers use their fat reserves to produce milk for their calves.

So it’s extremely important for whales to eat a lot and fatten up in the cold waters around Antarctica all summer long. But it seems there is not enough food. The whales arriving off the coast of South Africa are now thinner than they used to be.

This is the result of new research from Aarhus University. Since researchers began measuring right whales in the 1980s, whales have gotten thinner. This is explained by Fredrik Christiansen, senior researcher in the Department of Environmental Sciences at Aarhus University, who is behind the new findings.

“Right whales are 25 percent thinner than they were in the 1980s. This is bad for the whale population, because it means newborn whale calves are at a higher risk of dying. Fortunately, right whales in the Southern Ocean are not at risk but if this continues, They may become so.”

When the ice melts, the food is gone

When winter comes, and the cows leave the Antarctic and swim north, they have to acclimatize for several months without food. Several months in which they eat the fat reserves they accumulated during the warm and light summer season.

All summer long, right whales swim under the sea ice, opening their mouths to feed on sea bream, krill, and daphnia. The baleen inside their mouth is a kind of giant filter that filters out small animals from salt water. This allows the whales to eat large amounts of food without using up a lot of energy.

The krill shoals are shrinking, Fredrik Christiansen explains – meaning the whales can’t fatten up before winter like they used to.

“Shoals of krill live on phytoplankton, which thrive better in the colder waters around Antarctica. Here – like plants on Earth – they convert sunlight into energy. Higher sea temperatures mean fewer phytoplankton, fewer krill, and therefore fewer food for whales.

Instead, whales feed on food in the north, where there is another, less energy-rich, type of krill.

“In the north, there is less food for these small crustaceans. Therefore, they are not as big and fat as the animals that live under the Antarctic sea ice,” he says.

How do you weigh a whale

How exactly do scientists know that whales are getting thinner? Are Friedrich Christiansen and colleagues pulling megafauna out of the water with supersized scales? No, he explains. Instead, the researchers devised a way to calculate the weight of the whales based on images taken by drones.

“Right whales like to lie on the surface of the sea. This makes it easier to photograph them from above. When the drone takes some pictures – and we know the height of the drone – we can calculate the size of the animal,” he explains.

However, in order to find out the weight of a whale, it is necessary to know the size of the whale – not just the length and width. But because scientists like Frederik Christiansen have observed many right whales scurrying about on the surface of the sea over the years—and thus been able to measure their size—scientists now know the relationship between whale length, width, and size.

“We calculate the size using drone imagery – and when we know the size, we more or less know the weight. This way, we can see that whales have gotten thinner over the past 30 years – and that’s serious. The weight of mothers has a huge impact on their calves.”

Small and weak whale calves

Thirty to forty years ago, the average southern right whale calved every three years. But this is no longer true, as Friedrich Oskar Christiansen explains.

In the 1980s, researchers noticed that right whales off the coast of South Africa give birth to a new calf every three years. But since it is now more difficult for them to fatten during the summer, this has been reduced to every five years. This means that the population is growing significantly more slowly.

And it’s not just that whale calves are rare. Calves born today are smaller and grow more slowly.

“The amount of fat on a mother whale is directly related to the amount of energy she can give her calf through her milk. When the mother is thin, the calf gets less energy and grows slower,” he says.

Researchers have discovered that northern right whales in the waters off Canada and the northern United States are not growing as large as they used to be. This is probably because calves are born smaller. According to the researchers’ calculations, a whale born in 2019 will be an average of one meter shorter when it’s full grown than a whale born in 1981.

“Young calves are more likely to die. They are more likely to be attacked if attacked by a killer whale.”

Hunting is on the verge of extinction

Right whales were given their name because they were considered the “right” whales that could be hunted. People began hunting large whales as early as the 14th century, and for hundreds of years, they have been hunted fiercely in both the northern and southern parts of the Atlantic Ocean.

Whale blubber oil was one of the most important sources of energy. Train oil, once called oil, became fuel for lamps—both for indoors and for street lights. The demand for train oil was also one of the main reasons for Denmark’s colonization of Greenland in the 18th century.

Around 1900, train oil was replaced by another, more efficient energy source: crude oil. The black gold being pumped out of the ground meant that whaling was no longer profitable.

The southern right whale is one species that has benefited from the end of whaling. For over 100 years, the population has been allowed to grow large and healthy again. This is not only beneficial for whales, but also for the entire Southern Ocean ecosystem.

Because whales bring food to sea areas with little food.

Extremely important to the marine ecosystem

The sea around Antarctica where right whales eat has more life than any other sea on the planet. Despite the fact that the area contains only five percent of the sea water on Earth, 20 percent of all marine creatures live in the area.

Summer’s many hours of sunshine, turbulent sea currents, and cool temperatures are ideal for a bustling life.

The light makes the seaweed grow explosively. Ocean currents swirl and feed around the algae so that krill and plankton can wriggle in. When full, the tiny crustaceans multiply and form giant swarms. In some places, there may be up to 35,000 krill in a cubic meter of water.

Right whales – and many other animals – fill themselves with krill abundance, but unlike many other species, whales migrate thousands of kilometers north to spend the winter.

“Whales are extremely important to the parts of the sea where there isn’t much food. When whales die, their huge bodies sink to the bottom. In the depths, they become food for an entire ecosystem of eels, sharks, crabs, lobsters, worms and microorganisms,” says Friedrich Christiansen. .

Therefore, if whales disappear, this will have disastrous consequences for many other animals.

He concludes, “Whales are apex predators. When an animal at the top of the food chain disappears, it has a cascading effect. Animals all over the food chain will be affected if whales are no longer around. From sharks to bacteria.” .


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