Toothed whale

Toothed whales
Fossil range: Eocene–Recent
Bottlenose Dolphin
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Suborder: Odontoceti
Flower, 1869
Families

See text.
Diversity
Around 73; see List of cetaceans or below.

The toothed whales (systematic name Odontoceti) form a suborder of the cetaceans, including sperm whales, beaked whales, orca[1], dolphins, and others. As the name suggests, the suborder is characterized by the presence of teeth rather than the baleen of other whales.

Contents

Anatomy

Toothed whales have a single blowhole on the top of the head (while the baleen whales possess two of them).[2] The nostrils are not fused; one of them has become dominant over the other.

As an adaptation for their echolocation, toothed whale skulls have become asymmetric. Their brains are relatively big, although real growth didn't occur before their echolocation started to evolve. Toothed whales' brains have a poor connection between the two hemispheres and an organ called a melon on their heads is used as a lens to focus sound waves. Vocal cords are not present; their sounds are produced in the blowhole system instead. Toothed whales have lost their sense of smell, as well as their saliva glands.

Except for the Sperm Whale, most toothed whales are smaller than the baleen whales. The teeth differ considerably between the species. They may be numerous, with some dolphins bearing over 100 teeth in their jaws. At the other extreme are the Narwhal with its single long tusk and the almost toothless beaked whales with bizarre teeth only in males. Not all species are believed to use their teeth for feeding. For instance, the Sperm Whale likely uses its teeth for aggression and showmanship.

Behaviour

Vocalizations

Vocalizations are of great importance to toothed whales. While many species also maintain a broad variety of calls to communicate, all species investigated so far use short click sounds for purposes of echolocation. Sperm whales use low frequencies (a few to perhaps 50 Hz), while others employ more narrow-band high-frequency sounds (porpoises, Cephalorhynchus species like Hector's dolphin). Most dolphin species use very broad band clicks.

Movement

Most toothed whales swim rapidly. The smaller species occasionally ride waves, such as the bow waves of ships. Dolphins can be frequently encountered this way. They are also famous for their acrobatic breaching from the water, e.g. the Spinner Dolphin.

Human impact

Small whales are beset by a variety of anthropogenic threats including hunting, bycatch (entanglement in fishing gear), competition with fisheries, ship strikes, tourism (whale watching and "dolphin-assisted" therapy), live capture for display and research, habitat loss and degradation, industrial and military operations, chemical pollution, disease and biotoxins (e.g., from dinoflagellates) ozone depletion and climate change.[3]

Keeping small whales (mostly Bottlenose Dolphins, Orcas, or Belugas) in captivity is a great attraction for ocean parks and zoos. However, it is controversial because of the marine mammals' need for large spaces.

The Sperm Whale has been hunted commercially for a long time (see whaling). While small whales like the Pilot Whale today are still being pursued, the main threat for most species is accidental capture in fishing nets.

Currently there is no international convention that gives universal coverage to all small whales, although the International Whaling Commission has attempted to extend its jurisdiction over them. ASCOBANS was negotiated to protect all small whales in the North and Baltic Seas and in the northeast Atlantic. ACCOBAMS protects all whales in the Mediterranean and Black Seas. All whales (great and small) are listed in CITES Appendices, meaning that international trade in them and products derived from them is very limited.

Taxonomy

References

  1. ↑ "Integrated Taxonomic Information System". http://www.itis.gov. 
  2. ↑ Hooker, Sascha K.. Perrin, William F.; Wursig, Bernd; Thewissen, J. G. M. eds. Encyclopedia of Marine Mammals (2 ed.). 30 Corporate Drive, Burlington Ma. 01803: Academic Press. p. 1173. ISBN 978-0-12-3733553-9. http://www.elsevier.com/wps/find/bookdescription.cws_home/716899/description#description. 
  3. ↑ Reeves, R., B.D. Smith, E.A. Crespo, and G.N. di Sciara. 2003. Dolphins, Whales, and Porpoises. IUCN Species Survival Commission Specialists Group.