Why Did Whales Get So Big?
An Ancient L.A. Story
Blue whale vs T. rex
Which do you think would be bigger?
Blue whale and Tyrannosaurus rex illustrations
“Sue,” one of the largest T. rex specimens ever found, is 42 feet (12.8 meters) long and weighed an estimated 12,600 to 14,200 pounds (around 5,700 - 6,400 kilograms). Blue whales on the other hand, can reach up to 110 feet (33.5 meters) long and weigh 333,000 pounds (around 150,000 kilograms)! That means that blue whales can be as heavy as about 25 Tyrannosaurus rex and more than twice as long!
Blue whales are can be as heavy as 25 Tyrannosaurus rex and more than twice as long!
Whales got big
While the blue whale is the largest animal to have ever lived on Earth, baleen whales were not always so big. Baleen whales are a group of whales that use bristles called baleen to filter feed and include the blue whale and humpback whale.
The chart below shows how baleen whales have skyrocketed in size since they first appeared 34 million years ago.
Scientists use skull size as an estimate for relative body size
You can see that whale’s increase in size happened gradually over a period of around 20 million years ago, and then very dramatically in the recent geological past.
But why did whales get so big?
More food in the oceans
Krill are small crustaceans that range from 1 to 6 cm in length
Large animals need a large amount of food to live, and whales are no different. Blue whales, for example, can eat up to 4 tons of krill in a day. In order for these whales to survive, there has to be a lot of krill.
When there are more nutrients in the ocean, more krill can exist. More nutrients were available during periods when cold, deep ocean water would bring nutrients to coastal waters in a process called upwelling.
Baleen whales' growth spurt occurred over periods of increased upwelling when nutrient rich ocean waters could support larger populations of krill.
As baleen whales grew in size their need for large amounts of food also increased. Since whales are bigger than ever, they rely on a massive supply of food to meet their equally large need for energy.
How do whales find enough food to meet their huge requirements for energy?
Larger bodies can travel farther
There are only a few places in the world's oceans that have enough food for baleen whales.
In the winters, there is an abundance of krill under the ice sheets of Earth's polar regions. When the ice begins to melt away and food sources diminish, whales migrate long distances to their breeding grounds in more temperate latitudes.
Some blue whales migrate as far as 4,000 miles in the search of food and summer breeding grounds.
Whales time this migration with pulses of nutrients that supply them food on their journey. Many of the regions where they migrate exhibit seasonal upwelling.
The map shows generalized blue whale migration patterns and the regions of significant upwelling.
As you can see blue whales migrate very long distances. Some blue whales migrate as far as 4,000 miles in the search of food and summer breeding grounds.
Blue whales' massive bodies allow them to travel these long distances and take advantage of seasonal food sources.
A Californian krill buffet
Krill population size off the coast of California is seasonal. Krill feed on algae that produce chlorophyll. The abundance of algae in the ocean is in turn dependent on the nutrients supplied from seasonal upwelling.
The two maps show surficial chlorophyll levels in Winter (left) and late Summer (right).
Since the amount of krill that the ocean can support is dependent on their food source (chlorophyll producing algae), these two maps also show the abundance of krill.
Increased amounts of chlorophyll in the ocean are greatly influenced by the nutrients supplied from upwelling. Upwelling is at its strongest off the coast of California in the summer-autumn months.
Which month do you think has more food for whales?
Blue whales in California
Many baleen whales travel to the coasts of California to take advantage of the large concentrations of krill during the summer when upwelling is at its peak.
These two maps show surficial chlorophyll in Winter (left) and late Summer (right). The blue dots represent blue whale sightings.
As you can see in the maps, blue whales flock to the waters off the coast of California in September.
Blue whales usually first start appearing in Southern California around early June and migrate to equatorial waters in the winter to breed.
Longer migrations in a warmer ocean
Baleen whales travel long distances, sometimes thousands of miles a year, to find food sources and breed. As the world's oceans warm and krill populations are expected to decrease, many baleen whales will need to travel even longer distances to find enough food.
Longer migratory paths mean that whales would need to expend more energy to consume the same amount of krill. The advantage of being so large is being able to swim longer distances, but at a cost. Larger whales also have to consume more food to support their larger bodies.
As a warming climate threatens to disrupt the complex relationship between ocean currents, nutrients in coastal waters and krill populations, the future of baleen whales is uncertain.
