71 10.5 Marine Mammals: Whales

Marine mammals evolved within the last 60 million years from four-legged land ancestors who returned to the sea to increase their access to food. They’re most closely related to modern camels and hippos. Next time that you go to the National Aquarium in Baltimore, look up at the whale skeleton and look at the pectoral fins for a hint of the past. As a group, marine mammals share these common features:

    • 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)

 

Odontocetes (toothed whales): The Odontocetes, a parvorder of cetaceans, are the toothed whales and include the sperm whale, killer whale, dolphins and others. They’re generally smaller and less evolved than the baleen whales. They have powerful jaws for capturing prey and use echolocation to find their prey (a form of SONAR). This echolocation can be used to find their way around easily, even in murky water, and can be used to stun or even kill their prey. They’re considered to be very intelligent.

  • 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

A diagram of the anatomy of a baleen whale showing the baleen bristles in its mouth, two blowholes on the top with a splashguard, and ventral pleats on the bottom.
Public Domain

 

Blue whale

  • 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

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Introduction to Oceanography Copyright © by Cristina Cardona is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, except where otherwise noted.

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