Right whales losing serious weight due to climate change

In June, when winter arrives in the southern hemisphere and the waters around Antarctica freeze, a remarkable event takes place. Right whales begin their journey northward.

Many of them gather in the bay near the town of Hermanus in South Africa. The warmer waters of South Africa provide an ideal environment for these whales to mate and raise their newborn calves. However, there is a problem: there is no food for them in these waters. Throughout the winter, the mother whales rely on their fat reserves to produce milk for their calves.

It is crucial for these whales to consume large amounts of food and fatten up in the cold waters around Antarctica during the summer. Unfortunately, there seems to be a scarcity of food. Recent research conducted by Aarhus University has shed light on this issue. According to Fredrik Christiansen, a senior researcher at the Department of Ecoscience at Aarhus University, the right whales have become increasingly thin since the 1980s, when scientists began measuring their weight.

“Right whales have become 25 percent thinner compared to the 1980s. This is concerning for the whale population because it increases the risk of mortality for newborn whale calves. Although the right whales in the Southern Ocean are not currently endangered, if this trend continues, they could become so,” explains Christiansen.

When winter arrives, the whales leave Antarctica and swim north, facing several months without any food. During the summer, they feed on krill and water fleas, which they filter from seawater using their baleen, a filter-like structure in their mouths. This allows them to consume substantial amounts of food with minimal energy expenditure. However, the availability of krill has been decreasing, preventing the whales from fattening up before winter.

“Krill populations depend on phytoplankton, which thrives in the cold waters around Antarctica. Similar to land plants, phytoplankton converts sunlight into energy. However, rising sea temperatures have led to a decline in phytoplankton, resulting in fewer krill and less food for the whales,” explains Christiansen.

As a result, the whales are forced to search for food further north, where krill is less abundant and less energy-rich than their Antarctic counterparts.

To determine the weight of the whales, researchers like Fredrik Christiansen have devised a unique method that utilizes photographs taken by drones. Right whales tend to float near the sea surface, making them easily photographable from above. By taking drone photographs and knowing the height of the drone, scientists can calculate the size of the whale.

However, to determine the weight accurately, it is necessary to know the volume of the whale, not just its length and width. Through years of observation, scientists have discovered the relationship between the size measurements and volume of right whales.

“We calculate the volume using the drone photographs, and once we know the volume, we can estimate the weight. This method has revealed that the whales have become thinner over the past three decades, which is a serious concern. The weight of the mothers significantly affects the well-being of their calves,” says Christiansen.

In the past, southern right whales gave birth to a new calf approximately every three years. However, due to difficulties in fattening up during summer, the birthing interval has extended to around five years. This slower reproductive rate hampers population growth. Moreover, the newborn calves are smaller and exhibit slower growth.

“The amount of fat on the mother whale directly influences the energy she can provide to her calf through her milk. When the mother is thin, the calf receives less energy and grows at a slower pace,” Christiansen explains.

The research also indicates that the northern right whales in Canadian and northern US waters are not reaching their previous sizes, possibly due to smaller-sized calves being born. Accordingto the researchers’ calculations, a whale born in 2019 is expected to be, on average, one meter shorter when fully grown compared to a whale born in 1981.

Smaller calves face a higher risk of mortality, as they are more vulnerable to attacks by killer whales. This trend is deeply concerning for the long-term survival of the whale population.

Right whales earned their name because they were considered the ideal targets for whaling. As early as the 14th century, humans began hunting these majestic creatures in both the northern and southern parts of the Atlantic Ocean. Whale fat, particularly the oil extracted from it, served as a valuable source of energy. Known as train oil, it became a popular fuel for lamps, both indoors and for street lighting. In fact, the demand for train oil played a significant role in Denmark’s colonization of Greenland in the 18th century.

However, with the discovery of crude oil as a more efficient energy source around 1900, the demand for whale products declined, and whaling became economically unviable. This shift marked a turning point for the southern right whales, allowing their population to recover and thrive over the past century. This recovery has had positive implications not only for the whales themselves but also for the entire ecosystem of the Southern Ocean.

The sea surrounding Antarctica, where the right whales feed, is teeming with life. Despite covering only five percent of Earth’s sea water, it supports approximately 20 percent of all marine life. The combination of ample sunshine, turbulent sea currents, and low temperatures creates the perfect conditions for a vibrant ecosystem.

During the summer, the abundant sunlight fuels explosive growth of marine algae. The swirling sea currents distribute the algae and nutrients, creating a feast for krill and plankton. The resulting swarms of these small crustaceans can reach astonishing densities, with up to 35,000 krill per cubic meter of water in some areas.

Right whales, along with many other marine species, take advantage of this abundance by feasting on the plentiful krill. However, unlike other species, the whales embark on long migrations thousands of kilometers north to overwinter.

The role of whales extends far beyond their own nourishment. When these magnificent creatures eventually die, their enormous bodies sink to the ocean floor, becoming a source of sustenance for an entire ecosystem. Eels, sharks, crabs, lobsters, worms, and microorganisms all rely on the nutrients provided by whale carcasses.

Thus, the disappearance of whales would have significant repercussions for countless other animals in the food chain. Whales serve as apex predators, and their absence would trigger a cascade effect, disrupting the balance and vitality of the marine ecosystem.

In conclusion, the current decline in the physical condition of right whales, specifically their thinning and reduced reproductive rates, poses a serious threat to their population. The diminishing availability of krill, their primary food source, due to changing environmental conditions is a major concern. Not only does this impact the well-being of individual whales, but it also has broader implications for the marine ecosystem as a whole. Preserving the health and abundance of these majestic creatures is essential to maintain the delicate balance of life in the oceans. Efforts must be made to address the root causes of this issue and ensure the long-term survival of right whales and their invaluable contribution to the natural world.


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