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Why do whales migrate?
Every year, most whales swim from one part of the world to another and back again. Swimming takes up a lot of energy, so why would these aquatic creatures undertake such a journey? Here, we will learn a little bit more about these impressive globetrotters (or globeswimmers!).
What are the motivations for long-distance movement?
Migration is an important behavior for many walking, flying, and swimming animals. It is often a seasonally-driven movement over long distances. Whales achieve this by following Earth’s geomagnetic field, cues from the sun or moon, and by “talking” with other whales.
There are around 90 species of whales which all together make up an estimated 80,000 animals. That is a whole lot of whales! Many of these species are very large and therefore need massive amounts of food to support their basal metabolic rate and additional energy for their daily activities. This energetic demand creates a powerful drive for food like krill or fish. Whales will migrate toward cooler waters during the summer months to access more prey. However, the arrival of winter will bring severe drops in temperature and a decline in prey. It is now time to return to warmer waters.
This brings us to another motivation for migration: reproduction. Reproduction is important for the continuation of all living species. Once whales have returned to warmer waters, they may find a mate and give birth to a baby whale, also known as a calf. Calves are usually born to mature females only every 2-3 years. Since the birth rate of whales is so low, it is important for biologists to know the population number of all species. Populations with very low numbers are at risk of extinction.
Recently, scientists took a deeper look into why whales migrate. They asked, “Is food and reproduction the end of the story, or is there another benefit?” As these scientists followed killer whale movement from Antarctic waters to the south Atlantic Ocean, they saw that they were shedding many skin cells. When whales are in water that is too cold, they are unable to molt. The accumulation of old skin can lead to all sorts of problems such as bacterial infections. The movement through warmer water helps increase the sloughing off of this old skin, which improves animal health. In other words, don’t expect to find a whale getting a facial at your neighborhood spa! Nature has got this covered.
Do all whales migrate?
While all whales swim among different regions, not all migrations are created equal. Some species like humpback whales can cover great distances, while others have much shorter routes. For example, bowhead whales remain in the Arctic and subarctic waters throughout the year but will move among different regions within these cold waters. Conversely, a population of Mediterranean fin whales prefer the warmth year-round, and generally only move around within the central and eastern part of the Mediterranean Basin. Whale biologists continue to study the seasonal movement of these fin whales, who are genetically different from their more migratory North Atlantic cousins.
Within an animal population, some members of the group may migrate, while others may stay behind. It is not uncommon for an older or juvenile whale to stay and hunt the remaining prey in that area. Since juveniles are not yet ready to reproduce, they also lack the motivation to make the journey to breeding grounds. As these youngsters grow up, they will begin to follow the path carved out by their ancestors over the past several thousand years or more.
Are human-related activities impacting migrating whales?
We are currently living in the age of humans, otherwise known as the Anthropocene. Although mankind is always pushing the envelope to develop more advanced technologies, sometimes these products can have a negative impact on our wildlife and climates. This can include migrating whales and the waters they must journey through.
Whales partially rely on communication with their swimming groups, or pods, to stay on track during their migrations. If the pod happens to be passing through an area with noise pollution, such as sonar from ships, they may not hear each other and can get separated. In severe cases, the noise can be so loud that it can damage a whale’s ears and hearing, making it difficult to find their way back to the group. Since sound can travel much farther through water than in air, it is especially important for certain waters to be human-activity-free as much as possible.
Another human-related impact on whale migration is climate change. Climate is the gradual warming of the planet that is partially due to activities such as the burning of fossil fuels and deforestation. As the Earth warms, large sheets of ice melt at accelerated rates. How could melting ice affect migrating whales?
For some species, like belugas or narwhals, the ice forms paths that lead them from one location to another. Without this ice, current and future generations of whales can have trouble reaching the destinations needed for feeding or breeding. While scientists have found that many whale populations can adapt to environmental change, we still don’t fully understand how much change. Therefore, it is important for mankind to do as much as we can to maintain the health and balance of our Earth and life on it.
Fun fact: What has been the longest migration, and why?
A few years ago, a humpback whale held the longest whale migration record. This whale was first spotted off the coast of Brazil in 2001. Two years later, a tourist snapped a photo of the same whale off the coast of Madagascar. The minimum distance this whale must have swum was 6,000 miles, although this is most likely a significant underestimate since it probably took detours to feed on krill. The reason why this female humpback whale traveled so far remains somewhat of a mystery. Some scientists think that she was on a long search for food, while others say she may have been exploring new breeding grounds. She may have simply gotten lost along the way.
Today, the record holder is a gray whale, who swam 16,700 miles from the North Pacific to off the coast of Namibia, South Africa – halfway across the world. This is not only the longest migration record for whales but for any marine vertebrate.
Anthropocene: the current geological age, viewed as the period during which human activity has been the dominant influence on climate and the environment
Basal metabolic rate: the rate at which the body uses energy while at rest
Extinction: the dying out of a species
Migration: the long-distance movement of animals, often on a seasonal basis
Molt: a loss of feathers, hair, or skin
Pod: a social group of whales
Sonar: locating objects in air or water using sound waves
Vertebrate: an animal with vertebrae or a backbone
Whales: a common name for the group that includes all whales, dolphins, and porpoises
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