Blue whales are solitary animals, sometimes encountered in pairs, and they range throughout the world’s oceans. Humans have done the most damage to this magnificent animal, almost driving it to the brink of extinction. Blues have had complete protection by international agreement since 1965. Yet the three main populations have depressed numbers.
For whales and seals the ocean is not blue: a visual pigment loss in marine mammals
Most terrestrial mammals have colour vision based on two spectrally different visual pigments located in two types of retinal cone photoreceptors, i.e. they are cone dichromats with long-to-middle-wave-sensitive (commonly green) L-cones and short-wave-sensitive (commonly blue) S-cones. With visual pigment-specific antibodies, we here demonstrate an absence of S-cones in the retinae of all whales and seals studied. The sample includes seven species of toothed whales (Odontoceti) and five species of marine carnivores (eared and earless seals). These marine mammals have only L-cones (cone monochromacy) and hence are essentially colour-blind. For comparison, the study also includes the wolf, ferret and European river otter (Carnivora) as well as the mouflon and pygmy hippopotamus (Artiodactyla), close terrestrial relatives of the seals and whales, respectively. These have a normal complement of S-cones and L-cones. The S-cone loss in marine species from two distant mammalian orders strongly argues for convergent evolution and an adaptive advantage of that trait in the marine visual environment. To us this suggests that the S-cones may have been lost in all whales and seals. However, as the spectral composition of light in clear ocean waters is increasingly blue-shifted with depth, an S-cone loss would seem particularly disadvantageous. We discuss some hypotheses to explain this paradox.
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Are blue whales really blue?
That might sound like a funny question! After all, isn’t the blue colour of Balaenoptera musculus, in addition to its enormous size, the trademark feature of these giants of the sea? Not exactly. In reality, blue whales are not really blue: instead, their skin is light grey and speckled! If that’s the case, how did they get their name?
A deceptive colour
As a matter of fact, the blue whale is blue for the same reason the ocean is blue! Indeed, water acts like a filter for light: when light rays enter the sea, the red, yellow and green parts of the light spectrum, which have a shorter wavelength, are quickly absorbed and do not penetrate very deep into the water column. The colours in the blue part of the light spectrum, on the other hand, have a longer wavelength and thus go much deeper. Therefore, when an individual belonging to the species B. musculus is under water, its pale skin reflects the main light that reaches it, namely blue light. Its colouring is therefore rather deceptive due to the interactions between water and light!
Moreover, blue whales have not always been associated with their namesake colour. For some time, they were even associated with the colour yellow! In the 19 th century, American author Herman Melville nicknamed these mastodons “sulphur bottoms,” a term that was also widely used by American whalers at the time. Indeed, colonies of diatoms (phytoplanktonic algae) can develop on the bellies of blue whales, giving them a sulphur-like yellowish colour, hence this now archaic name.
The rarity of blue in nature
Blue is a very difficult colour to find in nature, as there is no naturally-occurring compound to colour living things blue. Yet there are plants and animals that sport vivid hues of this colour. But this is what is called a “structural colour,” meaning it comes from the interaction of light with the micro- and nanostructures found on an organism’s skin, fur or feathers. For example, peacock feathers contain microscopic ridges that interfere with light, cancelling out some wavelengths and magnifying others, hence their iridescent blue colour. As for the blue whale, however, it is not a structural colour, but rather the action of light on the water that gives it a bluish tint.
Not only do blue whales appear blue when observed from the surface, but also when viewed under water, where this effect is just as stark. They blend in with the cobalt ocean fog and are quite difficult to spot from afar. This therefore begs the question of whether the blue whale derives some sort of advantage from this colouring. Might it serve as camouflage for hunting or for evading enemies? Not necessarily! “The aquatic world is first and foremost an acoustic universe. Hearing often plays a more important role than sight in this context,” explains Richard Sears, president of the research centre MICS. “For example, if a blue whale is targeted by killer whales, which are one of its few predators, the latter have heard it long before they ever lay their eyes on it. Visually blending into its environment is therefore useless for the blue whale, since it has already been detected by other means,” he continues.
And it goes both ways. If blue whales’ colouring gave them some sort of advantage when foraging for food, then it would have an impact on their hunting success. In such a case, natural selection would favour a certain degree of colouration. However, this is not what we observe. “Pigmentation varies considerably between individual blue whales, so there is a chance that there is no connection whatsoever with their survival,” concludes Richard Sears.
Lastly, this trait may not have an adaptive or evolutionary function at all. “It could simply be a trait that has remained in the species because it is linked to another gene that has been subject to selection pressure. This phenomenon is called “selective hitch-hiking,” explains GREMM Scientific Director Robert Michaud.
But even if we don’t know why blue whales have this characteristic tint, and it may or may not offer them any benefit, the advantage for us is that we can easily differentiate them from other whales!
Blue Whale
DERIVATION: from the Latin balaena for whale; from the Greek pteron for wing-fin, from the Latin musulus, and diminutive of mus for mouse. (This may be meant as a joke since the blue whale is very different from a mouse, but it is also sometimes taken to mean muscular.)
At the ocean’s surface, a 27 foot high, slender, vertical blow reached toward the sky. As the 100 foot long body of the blue whale begins to descend, it reflects many shades of blue. As sunset fades to twilight and night, the color of the whale turns from shades of yellow to orange, pink, lavender, gray and black. The mottled back of the blue whale, due to its uneven skin pigmentation, reflects many color changes throughout the day.
This coloring may help it avoid detection by the krill upon which it preys. The largest animal to ever inhabit the planet feeds almost exclusively on one of the smallest animals — shrimp-like krill. A blue whale can ingest up to eight tons of krill per day, and it has 55 to 68 ventral grooves extending at least to the navel. These throat grooves expand to accommodate 40 to 50 tons of water and krill. The pouch, when filled, is the size of a large living room.
Blue feeding on krill – throat pleats are expanding
Close up of krill
When a blue gulps a mouthful of food, it is so fast that camouflage may not even be necessary. Speed was the key feature that protected the blue whale until about a hundred years ago when hunters obtained fast catcher boats and exploding harpoons.
The yellow coloration on its belly accounts for another of its names, “sulphur bottom,” and is caused by diatom accumulations formed during long stays in cooler waters. Richard Sears and his colleagues studying blue whales in the Gulf of St. Lawrence, Quebec, Canada, have been able to identify individual blues by the mottled pigmentation patterns on their backs.
Both sexes become sexually mature at 10 years of age at which time males are 67 feet and females are 72 feet. Females give birth to a single calf, 21 feet in length, every two or three years following a 12-month gestation period. The baby drinks 50 gallons of milk a day and is weaned at approximately eight months when it is 50 feet long and weighs about 50,000 pounds.
Blue whales are solitary animals, sometimes encountered in pairs, and they range throughout the world’s oceans. Humans have done the most damage to this magnificent animal, almost driving it to the brink of extinction. Blues have had complete protection by international agreement since 1965. Yet the three main populations have depressed numbers.
It is estimated that of the more than 5,000 that inhabited the North Pacific, only 1,200 to 1,700 are left. Only a few hundred are thought to survive in the North Atlantic, and of the 20,000 in the southern hemisphere in the 19th Century, about 9,000 remain (half of which are pygmy blue whales).
Blue whale blow can be 25 feet tall!
Blue whales are seen with some regularity in at least three areas: the coastal canyons off central and southern California; far inside the Gulf of St. Lawrence; and at the whaling grounds for fin whales in Denmark Strait.
Because of precariously low numbers, this whale is particularly vulnerable to habitat degradation and overfishing of its main food source, krill. A story about the merciless slaughter of blue whales was the inspiration that led to the formation of Save the Whales in 1976.
By: Maris Sidenstecker
DEAD BLUE WHALE WASHES ASHORE IN MONTEREY COUNTY CALIFORNIA A First-Hand Account
Baleen exposed in the mouth with strands of kelp caught in it.
A young female blue whale had probably been dead for one to two weeks when she washed ashore at Del Monte Beach near Monterey , California in early October 2004.
An effort will be made to determine the cause of her death. A nighttime necropsy done on the bloody carcass revealed that the whale’s stomach was empty. This only proved that she had not eaten in at least two days.
Researchers were led by Professor Jim Harvey of the Moss Landing Marine Laboratories. This was the first chance by many of the researchers and volunteers to see a blue whale up close. The juvenile whale’s skull and jawbones will eventually be put on display at the Marine Laboratories.
Side view with the pectoral fin clearly visible.
Pieces of blubber carved off the carcass were buried on the beach. Tests on the blubber’s thickness, as well as tests of fat content, may help to determine if starvation was the cause of death.
The rest of the 40-foot carcass will be towed 32 miles offshore and sunk in the 9500 foot deep Monterey Canyon.
The necropsy also showed infection by a type of parasite. Marine mammals typically have many parasites, even though they may be healthy. Professor Harvey suggested that the whale may have been infected by domoic acid, a naturally occurring neurotoxin that has been killing sea lions, otters and dolphins along the California coast. No one has documented domoic acid poisoning in blue whales, said John Calambokidis, a blue whale expert who is associated with the Cascadia research collective based in Olympia , Washington.
One of our recent newsletters contained an article (see below) about two new species of worms that devour whale bones. Observations can now be made on how quickly they begin to work on a fresh carcass.
A good look at the ventral pleats on the underside of the whale.
These expand when the whale feeds on large schools of krill.
Save The Whales has a small piece of blue whale baleen and a very large vertebrae presumed to be from a blue whale. The U.S. Government confiscated them from members of the public as they are from an endangered species. Permission was given to Save The Whales for their use. These artifacts are displayed in our hands-on outreach program, Whales on Wheels WOW™.
Of Worms and Whales
Two new species of worms have been discovered living on the bones of dead whales in California’s Monterey Bay. The strange worms do not have eyes, stomachs or even mouths. The discovery was made about 9,400 feet below the surface.
Robert Vrijenhoek, of the Monterey Bay Aquarium Research Institute, said that the worms have colorful, feathery plumes that serve as gills and green “roots” that work their way into the bones of dead whales.
They range from 1 inch to 2-1/2 inches and digest the fats and oils in the whalebones. Researchers named the worms a new genus Osedax or Latin for bone eating.
At first, researchers could not determine what kind of creature they had discovered. They concluded that the most recent common ancestor lived around 42 million years ago, or about the same time that whales first evolved.
