Baleen Whales Are Just the Size they Ought to Be

Humpback whale (Megaptera novaeangliae)

 IN THE HUNTER/GATHERER EQUATION, FILTER-FEEDING BALEEN WHALES came down on the gathering side millions of years ago. 

Gathering – in baleens’ case taking the form of filtering shrimp-like krill and other crustaceans, small fishes and phytoplankton out of the ocean waters with great baleen plates in place of teeth – has made them much more efficient feeders than their toothed cousins.

A study by researchers at Stanford University suggests that the largest whales grew to their bulky sizes from a need to generate sufficient body heat to survive in cold waters. But baleen whales’ ability to take in huge quantities of calories has helped make most of them larger than their toothy counterparts. But they’re not likely to grow even larger because…that would be too big.

A silhouette drawing of a blue whale (Balaenoptera musculus) comparing it to a human. A diver, of course. Image: Kurzon, under the Creative Commons Attribution-Share Alike 3.0 Unported license.


Blue whales – baleens who weigh in at 150 tons and 100 feet or so – are the largest animals on Earth. They can charge through a mass of krill (each weighing in at about 2 oz.) with their mouths open to 80 degrees, inflating like a parachute and taking in enough water to equal their own body mass. With each krillish mouthful, according to a separate study, they can acquire 457,000 calories in crustaceous protein, quite a deal considering the energy they expend.

As carnivores, toothed whales have to hunt down individual prey, expending high energy for a lower caloric return. The sperm whale – the largest toothed whale at about 45 tons and 50 feet in length – is famous for making dives to as deep as 3,000 feet, lasting as long as an hour, to hunt giant squids. And for returning with the sucker marks of squids that don’t go willingly.

A section of baleen from a filtering whale’s mouth. Often compared to Venetian blinds, baleen is primarily composed of keratin, the same substance that makes up fingernails.


Some 90 species of whales roam our planet’s oceans, all members of the suborder Cetacea. The baleen family (Mysticeti) encompasses about 15 species, the toothed whales (Odontoceti) about 73 (including 46 species of much smaller dolphins and porpoises, usually discussed as a separate group).

While a common perception of whales may be of animals with large, square heads – that is, the sperm whale design, thanks to the most famous whale of all, Moby Dick – the big-headed boxy shape is an outlier. Nearly all whales, baleen and toothed, big and little, are pretty much torpedo-shaped, no matter their size.




For a long time, it was thought that sea-going animals ballooned in size because life in a watery environment freed them from the constraints of gravity.

But in their paper published in Proceedings of the Royal Academy B,  the Stanford University scientists suggest that large size reflects the need for bodies that can amass the immense numbers of body cells required to maintain body heat in ocean environments. They add that the volume-to-surface ratio is smaller in animals with massive bulk than in smaller ones, enhancing the heat-conserving factor.

They note that marine mammals in general are far larger than their land-based relatives – not just whales but sea lions, seals and walruses. The largest whales are far bigger than the hippos they diverged from, sea lions larger than bears, for example (they don’t mention the significant of layers of blubber as a factor in heat conservation. And, there are exceptions to the bigger-is- beautiful algorithm. Sea otters are definitely small animals – but with lots of fur).

Bowhead breaching.


The transition of land mammals into animals suited for life in the seas some 50 million years ago and the development of baleen lifestyles some 30 million years ago came about as adaptations designed to maximize access to food.

Separate research by scientists at Smithsonian’s National Museum of Natural History and Stanford has suggested that the gigantic whale species we know today are relatively recent. The emergence of gigantic species came only some 4.5 million years ago, possibly because the beginning of the last great ice age triggered a change from consistent warmth to season cooling, boosting the food supply by enhancing upwelling of nutrients from the depths and runoff of nutrients from land-based glaciers.

The ballooning of sizes developed independently in at least three different baleen lineages – the fins and humpbacks, the blues and seis, and the rights and bowheads.

There are limits. The Stanford researchers suggest that if whales were to keep evolving to ever-larger dimensions, their metabolisms would speed up to the point that taking in enough food would become impossible.


Not addressed in this long post – and an urgent, continuing story – is the perilous status of most whales, decimated by whale hunting in the 19th and 20th Centuries. Until an international moratorium on whaling was instituted in 1985, the population of humpbacks, for example, had been reduced by 95 percent.

Humpbacks, to continue the example, have since shown signs of recovering but today they and other whales still face threats from entanglement in fishing gear, being struck by ships, ocean noise, pollution and habitat loss. Beluga, blue, bowheads, false killer, fin, gray, humpback, North Atlantic right, North Pacific right, sei, southern right and sperm whales are all considered endangered under the Endangered Species Act.

Even more dire, many scientists worry, is the potential loss of habitat poised by climate change. As the oceans warm, food supplies like Antarctic krill may be sharply diminished.

The trouble with whale watching is that they live underwater and most people’s view of them are limited to breaching and diving, like these flukes of a humpback.


  • Killer whales – “orcas” – and pilot whales are actually members of the dolphin family (Delphinidae) but are usually listed with large whales because of their sizes. A few dolphins reach up 10 feet in length but most are in the 5-to 9-foot range.
  • Blue whales that live in the Northern Hemisphere generally grow to about 90 feet. Blue whales found in Antarctic waters measure up to some 110 feet because of the much richer krill environment found there.
  • Gray whales (Eschrichtius robustus, 42 to 49 feet) are baleens with a singular approach to collecting food. Swimming to the seafloor, they lie on their sides, stirring up sediment and, with it, tiny crustaceans, mollusks and other edibles that live in the sand.
  • The length and number of baleen plates each whale has depends on its species. Not surprisingly, blue whales have the longest baleen among whales – sometimes more than 350 plates some 12 feet in length.
  • Baleen is always attached to the whale’s much-larger upper jaws, giving them the appearance of a rather stoic grin.
  • Baleen plates become splintered by abrasion from the whale’s tongue and the constant whooshing of water, creating bristle-like fringes that are essential for filtering small organisms.
  • Baleen whales have two blowholes for expelling water but toothed whales have only one.
Short-finned pilot whales, clearly revealing the single blowhole of toothed whales.
  • But toothed whales have a capability for echolocation – sending out sound waves to locate prey – that baleens don’t. It’s suspected that the Odontocetes’ second blowhole was adapted for use in echolocation.
  • Some whales, like humpbacks, migrate great distances through the year, following the food train. Some blues may migrate, some stay year-round in Antarctic waters – again, food. Belugas and narwhals live full-time in Arctic waters; their lack of dorsal fins facilitates their swimming under the ice.
  • Narwhals are toothed whales with a vengeance. All males and some females have a tooth that grows into a unicorn-like horn, a long clockwise-spiraled tusk.The tooth both serves both as a sensory organ and is used to spear fishes.
  •  It’s believed that bowhead whales (can live for more than 200 years and that killer whales can live for more than 100 years.
  • It turns out that keratin-based baleen is somewhat like tree rings, compared to chemical timestamps that yield information about the animals’ lives. Scientists are studying it to understand baleens’ health, travel and reproduction.


For a comprehensive NOAA guide to whale shapes, sizes and other details, click here. 


PRINCIPAL SOURCES: “Whales,” National Oceanic and Atmospheric Administration; “Dolphins and Porpoises,” NOAA; “Independent evolution of baleen whale gigantism linked to Plio-Pleistocene ocean dynammics,” Graham J. SlaterJeremy A. GoldbogenNicholas D. Pyenson, Proceedings of the Royal Society B; “Sea mammals are huge for a reason,”  Angus Chen, Science Magazine news feed;  “What should I know about baleen whales?” Marine Mammal Laboratory, NOAA Fisheries; “Whales Swallow Half a Million Calories in Single Mouthful,” Wynne Parry, Live Science; “Ancient Gap-Toothed Whale Led to Evolution of Efficient Filter Feeding,” “Whales Only Recently Evolved into Giants,” Jen Viegas,;  “Dolphins & Porpoises,” NOAA; “10 Wonderful Whale Facts,” NOAA; “Why Did the Biggest Whales Get so Big?” Ed Yong, The Atlantic; “The Oral History of Toothless Whales,” Jennifer S. Holland, Hakai Magazine; “Whale Facts,”; “How narwhals use their tusks,” Adam Ravetch, World Wildlife Fund.










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