Unit 2: Cetaceans

A Blue Whale, Image from Arkive.org

The Classification of Cetaceans

Whales and dolphins are members of the kingdom Animalia, phylum Chordata, and class Mammalia.  That means that whales and dolphins are mammals, not fish.  They give birth to their young rather than lay eggs.  They nurse their young through mammary glands, and they give extensive parental care to their offspring.  Collectively, we place all of the 80-90 whales and dolphins in the order cetacean. Cetus from the Latin meaning whale. Cetaceans are generally placed into two distinct sub-orders the Mysticeti (whales with baleen) and Odontoceti  (toothed whales.)

The Evolution of Whales

Whales and dolphins are mammals, having evolved from land based mammals.  Marine Mammals have a lot of features that are not ideally suited for life in the ocean.  Like other land mammals, whales and dolphins breathe air, limiting them to life at the surface.  They are warm blooded and most species struggle to maintain high body temperatures.  They have a spine and pelvis that moves up and down like other mammals, rather than the side to side movement of fish.  The bone structure of their fins matches that of hoofed land mammals rather than fish. They nurse their young with milk and most species have hair or fur.  Additionally, many whales have residual leg bones that are no longer attached to their pelvis.

Fossilized bones from the Valley of the Whales in Egypt. Image from Wikipedia Commons

A great diversity of whale and whale ancestor fossils tell a compelling evolutionary story of the movement from land to water.  Ancient whale ancestors moving into the water to take advantage of abundant food resources and gradually over time evolved into highly successful modern whales. Watch a video clip from PBS Evolution to learn more about whale evolution.

The embryological development of whales living in the present also tells a story of their evolutionary history.  In many embryonic whales, external hind limb buds are visible for a time but thendisappear as the whale grows larger.  Some whale embryos will develop hair and rudimentary ear pinnae, which disappear before birth.  In some whale species developing embryos start off with nostrils in the front of their head like land mammals, only to have these migrate backwards to the blow hole position as the embryonic whale continues to develop.

Mysticeti (Baleen Whales)

Description: Mysticeti are the largest living animals that have ever existed on Earth. They are larger than elephants, and some even larger than the largest of the dinosaurs.  Blue Whales, the largest whale species on Earth, have an average adult length of 80 feet (24 meters) and have been measured to 98 feet (30 meters). It is impossible to weigh such an animal, but estimates have put the large ones near 190 metric tons. What gets lost in that size is how long and sleek these animals are. Blue whales are also some of the fastest swimming animals in the ocean, reaching 50 kilometers per hour for short distances. All baleen whales have large convex skulls with attached baleen plates hanging down from the maxilla of their skull.  Baleen whales also have a large double nostril blow hole.

A Bowhead Whale, Image from Arkive.org

Feeding: Aside from their size, the mysticeti’s most distinctive feature is the baleen plates that hang down from their top jawbone. Whales use these baleen plates to filter out small food items such as krill, herring, and plankton. It may seem strange that the largest animals on earth would feed on organisms that are frequently less than an inch long, but from an ecological perspective it makes perfect sense. Krill, copepods, and other types of plankton are some of the most abundant (by weight) forms of life on Earth.

All baleen whales are filter feeders, but different whales use a variety of different strategies for capturing food. Some, like bow head whales, have exceptionally long baleen.  They will skim the surface of the water with mouths agape, gathering small phytoplankton in their mouths. Some, like blue and fin whales, will swim quickly into schools of prey, gulping up huge schools of prey at a time and filtering out the water as they close their very large mouths.  Gray whales, who have very short and stiff baleen, feed by scraping the side of their heads along the bottom, sucking up mouthfuls of sediment and filtering out the crustaceans living in the mud. Humpback whales have some of the most interesting feeding style of all. They will often feed in small groups producing nets of bubbles to entrap schools of fishClick on any of the links to watch video of their feeding style.

Life Cycles: The life cycle of most baleen whales includes late reproductive maturity, long gestational periods, and calves every 3-4 years. Baleen whale mothers will nurse their calves for up to two years. Most species of baleen whales make great migrations with calving often taking place in calm shallow and protected waters. Click to watch a gray whale with her calf. Most baleen whales feed in the colder and more nutrient rich waters of the higher latitudes.  Baleen whales are generally considered less social than their gregarious cousins the tooth whales, but they will form small feeding or mating groups. Baleen whales have a variety of courtship styles; they are can be highly competitive, often elaborate, and sometimes aggressive.  Male humpbacks, the most unique in this regard, participate in an annual “sing off” to attract potential female mates.

Behavior: Observing whales can be an exciting experience. This is despite the fact that they spend much of their time underwater. Several obvious behaviors can be observed when whale watching. Whales will often stick their heads out of the water to look around in a move called spy hopping. Sometimes they throw themselves completely out of the water in a move called breaching. Whales may also slap their fins or flukes (tails) to make sounds that can be heard for great distances.

Odonticeti (Toothed Whales)

Description: With the noted exception of the sperm whale, the toothed whales are smaller than the baleen whales. They have highly developed brains and are aggressive predators. Toothed whales have concave skulls with a large bulbous organ called a melon, which they use to focus sound.

A common dolphin, image from Arkive.org

Behavior: Toothed whales are defined by their social groups that are typically large extended families led by a matriarchal head. Males, especially male sperm whales, are more likely to be isolated into “bachelor groups.” Smaller groups will often come together to form larger “super pods” for the purpose of mate selection. Dolphins and toothed whales give the appearance of being highly playful, putting on frequent aerial and acrobatic displays. Dolphins are often observed riding the waves, pushed by the front of boats in a behavior called bow riding or even surfing.

Feeding: As in all things, toothed whales feed in groups. Often, working collectively as unit, they are highly adapted hunters. Click to watch a video of a pod of killer whales attacking a much larger gray whale. Dolphins have been observed to successfully corral fish into shallow areas where they are easy to eat. Even more remarkably, killer whales will sometimes beach themselves onto shallow beaches when going after pinnipeds or penguins. Toothed whales make extensive use of echolocation to locate, and in some cases can use sound to disable or “stun” their prey. Sperm whales, in particular, have a large arsenal of sounds to locate and disable their prey. Their skills at hunting are so well adapted that large schools of tuna will often follow below pods of dolphins, taking advantage of the dolphins ability to locate prey through echolocation. Some groups of toothed whales are migratory, and others prefer to stay in local habitats. Toothed whales will often dive to great depths in the search for prey (particularly squid). Most notably, sperm whales can dive to depths of three kilometers and stay down for over an hour.

Questions to Research

  1. Cetaceans are a group that includes all baleen whales and dolphins.  Using Arkive: Family Balaenopteridae, write a description of one baleen whale.  Using Arkive: Family Delphinidea write a description of one toothed whale.  Describe one way baleen whales and toothed whales are similar and one way that they are different?
  2. Beaked whales are the most interesting toothed whales that most people have never heard of.  Go back to Arkive.org and describe two things you learn about two of the species of beaked whales featured.
  3. Describe three pieces of evidence that whales have evolved from land mammals.
  4. Watch a short video from NOAA on tagging whales in Antarctica.  Describe how they tag whales as well as what they learn about the whales behavior from these tags.
  5. Read the above text, click on any of the linked videos on baleen whale feeding strategies.  After watching them, describe each of the strategies (gulping, skimming, bottom feeding, and bubble netting) in a few sentences. In your description, try to include their swimming motion as well as how they use their baleen.
  6. North Atlantic Right Whales were considered to be the “right” whales to hunt because of their slow moving behavior and the tendency of their bodies to float when killed.  Although they are no longer hunted, explain what risks these most endangered of whales are facing.  If you need a feel good moment, watch a NOAA team liberate a North Atlantic Right Whale from fishing gear in which it had become entangled (YouTube).
  7. Use the following information and the long piece of paper you were given in class to create to scale (1 Meter= 1 Cm) drawings for the following 6 species. Your drawings can be very simple, but pay attention to the scale. [Human – 2 meters, Beluga – 4 meters, Blue Whale – 32 meters, Fin Whales – 27 meters, Sperm Whale – 24 meters,  Killer Whale – 9 meters.] If you are struggling to make the drawings, look up each species in Wikipedia.  This infographic may help you.  Finally, just for fun, type “blue whale skeleton, Santa Cruz, CA” into google maps. Zoom in all the way in. Comparing this reconstructed skeleton to the cars and buildings should help you understand how big these animals are.
  8. Whales as ecosystem engineers.  What is meant by that term and how do whales stabilize ecosystems?
  9. As cetacean’s go, gray whales are distinctive in their appearance and in their feeding style.  They spend their summers feeding in Alaska’s food rich waters where they are studied by NOAA biologists.  Describe two things you learn about how Gray Whales are unique.
  10. Odonticeti (toothed whales) are long lived, intelligent, and highly social.  They typically live in matrilineal groups led by older females.  As such, different family groups, develop different cultural rules and behaviors.  Describe two cultural differences between transient and resident orca groups.