71 10.5 Marine Mammals: Whales
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- a streamlined body shape for more efficient movement through the water
- a high metabolic rate that generates a lot of heat and layers of fat and, in some cases, fur, to conserve this heat
- modifications to their respiratory system to collect and retain large volumes of oxygen to allow deep and repetitive dives
- osmotic adaptations that free them from any requirement for fresh water
Order Cetacea: the whales
- Whales also have special adaptations, such as:
- A thick layer of blubber
- Their nostrils have migrated to the top of the head so that the animal doesn’t have to come completely out of the water to breathe
- Large, deeply convoluted brains
- A special skin that “gives” to dampen out irregularities in water flow
- Bronchial cartilage that supports their lungs against pressure during deep dives
- Their blood is especially rich in hemoglobin to store more oxygen for diving
- They can slow their heartbeat while diving
- The blood supply can be reduced to all but the vital organs while diving, to conserve oxygen
Whale groups come in two ‘flavors’ (sub-Orders) – Odontocetes (toothed whales) and Mysticetes (baleen whales)
- Sperm whales are the largest of the toothed whales, reaching lengths up to 60 ft
- It also possesses the largest brain ever to have evolved on Earth
- They can dive to greater depths than any other air-breathing animal – to 3000 ft – and can stay down for over an hour
- Their head is filled with up to a ton of clear oil, presumably used to focus sound waves passing to their prey and back
Mysticetes (baleen whales): Also known as baleen whales, the Mysticetes are considered to be more highly evolved than the Odontocetes. Baleen is a bristly, bush, fibrous substance set in the jaws in overlapping plates; it looks like a gigantic comb.
- They feed on small planktonic arthropods (krill)
- Baleen is a straining mechanism
- The whale takes in a big gulp of water, closes its jaws, raises its tongue to expel the water, and the food is caught on the surface of the baleen
- The food is swallowed after being licked from the baleen by the whale’s giant tongue
- Baleen whales include the blue, humpback and gray, among others
- The blue whale is probably the largest animal ever to have lived on Earth
- They’re usually described as up to about 100 feet in length and up to about 200 tons
- this compares to three railroad cars in length and about 1600 people in weight
- Blue whales feed on krill, which are tiny shrimp-like crustaceans
- A mature blue whale consumes about 4 tons of krill per day when it’s feeding
- For a 7 to 8 month period; it fasts when it is in tropical waters
- From December through April, the blue whale gorges on krill around the Antarctic
Humpback whale
- Humpbacks are stocky and seldom exceed 50 ft in length
- They’re generally black above and white below, with extremely long, wing-like flippers
- They’ve become known for their “song”, which are sounds with definite patterns and sequences
- All the whales in a given population sing the same song, but the song changes every year
- Humpbacks are also very acrobatic, at times leaping completely out of the water
- It is estimated that there are no more than 10,000 humpbacks surviving today
Gray whale
- The Gray whale is the only large whale with a heavily mottled appearance and a knobby ridge down the back
- Its ‘natural’ color is dark gray or black, but it’s covered by a profusion of spots, scars, patches, and clusters of barnacles, which gives it a mottled, grayish appearance
- The Gray whale makes the longest migration of any mammal, an annual round-trip of some 10,000 miles from the Bering and Chukchi seas in the high Arctic to the warm lagoons of Baja California
- They were easily caught by whalers and almost became extinct in the 1940’s
- Given full protection in 1946, they’ve made a successful comeback and their population, estimated at about 21,000, is now believed to be inline with the carrying capacity of their range
- The Gray whale is the most heavily parasitized of all cetaceans – playing host to three species of lice, some over an inch long – in one case, more than 100,000 of one species of louse were removed from a single whale
Dr. Cristina Cardona