Log Transcript

This is Genevieve Johnson speaking to you from the Odyssey in the Indian Ocean.

As we began our 1600 nautical mile passage from the Maldives in the Northeast to Mauritius in the Southwest, the crew sighted sperm whales, risso's and pan-tropical spotted dolphins. We look forward to seeing many more species over the coming weeks.

As the education director aboard the Odyssey, I am often asked - "how many species of cetaceans (whales, dolphins and porpoises) are there?"

Bearing in mind that the classification of cetaceans is fluid, the current count puts the number of whales, dolphins and porpoises living in the world's seas, oceans and river systems today at 86. These 86 animals are further divided into two groups - Mysticetes - (baleen whales) and Odontocetes - (toothed whales).

The two sub-orders are distinguished from one another primarily by the presence or absence of teeth. The feeding apparatus of Mysticetes has been modified into fringed plates of keratin called baleen. Baleen is used to filter small fish and marine organisms such as krill from the water. Odontocetes use their teeth to grasp their prey individually - usually squid or fish and sometimes other marine mammals, however, they do not chew.

Baleen and toothed whales also differ in several other ways. Baleen whales are all great or large whales, usually exceeding 10 meters in length. The largest baleen whale, the blue whale, is the largest animal ever to have lived on our planet at over 30 meters and 150 tons, whereas the only toothed whale longer than 10 meters is the sperm whale. Although toothed whales tend to be smaller than baleen whales, male Odontocetes are sometimes considerably larger than females. In baleen whales it is usually the female who is slightly larger than the male.

Odontocetes have diversified and entered many more niches than the Mysticetes, including rivers, estuaries, coasts and oceans.

Toothed whales include sperm whales, narwhales and belugas, beaked whales, oceanic dolphins - including orcas and pilot whales, porpoises and river dolphins.

Baleen whales include the right whales, blue, fin, Sei, Bryde's and Minke whales, Gray's and humpbacks and the pygmy right whale.

Whenever the crew sights a species of baleen whale at sea, we are able to distinguish it from a toothed whale almost immediately by the size of the animal and the number of blowholes. Baleen whales have a symmetrical skull, with two external nostrils or blowholes. Toothed whales have a single blowhole - the nasal passages joining below the surface. Their jaws often extend out as a beak, behind which the forehead rises to a rounded Ômelon'. It is believed that the oil filled melon is used by toothed whales for echolocation - high frequency bursts of sound that reflect from their prey. Baleen whales have not been shown to be capable of echolocation.

Toothed whales are very social and tend to spend their lives immersed in family groups - mature male sperm whales are an obvious exception. This morning the crew experienced the pleasure of observing 30 pan tropical spotted dolphins riding Odyssey's bow wave. We often see groups of Odontocetes numbering in the hundreds, occasionally we have observed them in their thousands.

Baleen whales on the other hand are generally solitary, only coming together to mate or feed. We usually encounter these animals on an individual bases, although when food is abundant, we have seen up to six blue whales feeding in close proximity to one another.

Modern cetaceans encompass two suborders, the Mystecetes (baleen whales) and the Odontocetes (toothed whales).

Odontocetes, like this sperm whale, have a single blowhole.

Photo : Chris Johnson

Mysticetes, like this blue whale, have two blowholes.

Photo : Chris Johnson

The Order Cetacea, is comprised entirely of aquatic mammals. Mammals first evolved more than 200 million years ago as air breathing, land dwelling animals. The die-out some 66 million years ago of the large reptiles led to a massive expansion of mammal species. The earliest known true whales - marine mammals, appeared shortly after this massive reptilian die-out, about 50 million years ago.

The evolutionary roots of modern whales can be traced back to a common ancestor of even-toed ungulates, meaning that the closest living relatives of cetaceans today are hippos, pigs and camels.

Like all mammals, cetaceans are warm-blodded, breath air, give birth to live young that they provide with milk - usually a single offspring. They also have hair, although in whales, it is reduced to a line of hair follicles on the head, most noticeable in young animals, but found on all animals of any age.

Although sperm whales - the largest of the Odontocetes are our primary focus, we are always looking for other species to record in our sightings data. That data, combined with the work of other scientists, will help give us a clearer overall picture of the distribution and abundance of cetacean species throughout the Indian Ocean.

We look forward to sharing our sightings with you over the coming weeks.

Links:

• What did the crew report on one year ago in the Seychelles?
  Two years ago in Australia?
  Three years ago in Kiribati?
• Learn more about the evolution of whales.

Written by Genevieve Johnson

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