A blue whale spotted off the coast of Monterey, California.
Credit: Chase Dekker/Shutterstock
The blue whale (Balaenoptera musculus) is the largest animal
known to have existed in history. These enormous marine mammals have
been known to reach up to 110 feet (34 meters) long, and the largest
individuals likely weigh at least 150 tons (136 metric tons), according
to the National Oceanic and Atmospheric Administration (NOAA) Fisheries. That's a little more than twice the length of a school bus and more than three times the weight of a semitrailer truck.
"You never cease to be impressed by the force and presence of these
animals," said Richard Sears, a marine biologist and founder of the Mingan Island Cetacean Study,
a nonprofit research organization that studies marine mammals. The full
enormity of a blue whale may not be obvious from above the water's
surface, but "when you're next to a blue whale underwater, it's
magnificent," Sears said. "That's when your heart gets pumping."
Taxonomy and evolution
Blue whales belong to a group of whales called rorquals, which are
baleen whales with folds or grooves in their skin that allow their
mouths to expand to swallow larger volumes of water when feeding. Many
scientists describe blue whales as belonging to one of three subspecies,
with groups found in the Northern Hemisphere and the Antarctic, and a
third, the pygmy blue whales (B. musculus brevicauda), in the Indian and Southwest Pacific oceans. Pygmy blue whales are smaller whales, but they may still grow to 79 feet (24 m) in length.
The distant ancestors of blue whales
had legs and walked on land, but ventured into the water to find food.
Over many generations, these creatures developed adaptations suitable
for living in water full time, such as fins, blubber and blowholes.
Although the fossil record is murky, research suggests
that some of these animals lost their teeth and fed by sucking their
prey into their mouths. These ancient, toothless whales are thought to
have eventually developed baleen — brush-like plates with small gaps —
to filter food out of the water they were sucking in.
Research published in 2017 revealed that blue whales likely began growing to such tremendous size only relatively recently, from an evolutionary standpoint — perhaps in just the past 3 million years.
Blue whales have been successful in reaching their humongous size
because their water environment supports most of their mass compared to
animals on land, and they've adapted to feed so efficiently on krill,
Sears said. [Whale Album: Giants of the Deep]
Diet and habitat
Blue whales are found in oceans around the globe. Scientists keep track
of populations in the North Pacific and Atlantic Oceans, as well as
whales throughout the Southern Hemisphere.
The whales migrate long distances to find food in cold waters and rear
calves in warmer areas during the coldest few months of the year. These
trips extend from the tropics to the polar circles and cover thousands
of miles.
Some whales have been spotted returning to the same locations year
after year, but not always. Searching for whales by boat has its
limitations, Sears said, so it often isn't clear to researchers if the
"missing" whales just went somewhere else that year, or simply weren't
seen by whale spotters.
Blue whales almost exclusively eat krill — small, shrimp-like
creatures. The whales seek out large concentrations of their tiny prey,
which they engulf in a large amount of water, sometimes spinning about
as they do it. The water in one of those massive gulps weighs as much
as the whale itself, Robert Shadwick, an animal biomechanics researcher
at the University of British Columbia, previously told Live Science.
The whales push the water back out across their baleen filter, which
catches the krill. Unlike toothed whales, blue whales lack teeth and
instead have baleen, which are thin, semirigid plates that grow down
from the top of the whale's mouth. The plates are lined up closely to
one another and are made of a protein called keratin — the same protein
that builds fingernails and hair. The amount of krill a blue whale
captures in one gulp of water may provide nearly half a million calories
of energy.
A blue whale engulfs krill off the coast of California.
Credit: Copyright Nicholas Pyenson/Silverback Films/BBC
Life cycle
Scientists estimate that blue whales may live as long as 80 to 90
years. Sears has been tracking blue whales in the North Atlantic Ocean
for over 40 years, and he continues to see some of the same individuals
that he saw when he first started.
One of the reasons blue whales are able to live so long is their lack
of predators. Blue whale calves are small enough that they're
occasionally targeted by orcas, but adult whales are so large that even
the most vicious ocean predators steer clear. Humans pose the biggest
threat to a blue whale's survival.
Blue whales can communicate over long distances with extremely loud, low-pitched calls that are below the range of human hearing. Scientists are still learning about the context for these calls and mating behavior.
Blue whales appear to reach sexual maturity
somewhere around 9 years old, but researchers and whale trackers have
been unable to determine if there are specific breeding-ground regions
for blue whales.
What scientists do know, however, is that mother blue whales usually
give birth to single calves, which are 20 to 23 feet (6 to 7 m) long,
and weigh up to 6,000 lbs. (2,700 kilograms). Calves nurse for six to
eight months and may stay with their mothers until they are around 2 to 3
years old.
Conservation status
The World Wildlife Fund
lists blue whales as endangered. Commercial whaling is no longer the
major threat it once was, but climate change, pollution, human-made
noise and shipping traffic are still concerns. Nonetheless, according to
the International Union for Conservation of Nature and Natural Resources (IUCN), the global population of blue whales is increasing.
Sears estimates there may be anywhere from 10,000 to 18,000 blue whales
worldwide. It's difficult for experts to determine a more exact
population size because blue whales traverse such vast portions of the
ocean, which makes them tough to track, Sears said. "We don't really
have a handle on it."
And although blue whales are gigantic creatures, they're still really
good at hiding from humans. The whales can frequently hold their breath
for 20 minutes at a time and travel long distances in that time, which
makes it difficult to follow them, even once they've been spotted, Sears
said. "The study areas we give ourselves can already be pretty broad in
terms of humans, but in the scale of blue whales, it's a joke," he
said.
Sears estimates that researchers may glimpse only 5 percent of the blue
whale's life when they come close enough for observation. The remaining
decades of a blue whale's life may become easier to document with
technology like drones and improved satellite tags. It may take two or
three generations of biologists, said Sears, before there is a
"comfortable" understanding of blue whale behavior and social
interactions. Further reading:
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