Week 3
17 July 2006

Cetaceans of the Southern Ocean

Week 1 was about albatrosses and petrels. Here’s a more poetic description of a petrel submitted by Alison Cleary. (See “The Team” for more information on Alison.)

---from The Worst Journey in the World by Apsley Cherry-Garrad.

Cetaceans (see-TAY-shuns) part I

4 Killer Whales swim Photograph by: Donald LeRoi, NOAA Southwest Fisheries Science Center National Science Foundation Link

Whales, dolphins, and porpoises are all considered cetaceans. The Antarctic and Southern Ocean ecosystem has been estimated to hold more than 50% of the world’s marine mammals. Whales can be divided into two categories. One is baleen whales who filter feed on plankton or small fish. The mouth of the baleen whales is adapted to the size of the food consumed. The other category is toothed whales. More is known about baleen whales because of their importance to whalers.

Question: If a baleen whale eats only plankton, will the mouth filter be coarse or fine?

Annual consumption of krill is estimated at 150 million metric tons. (Krill is a type of zooplankton; it is a small crustacean.)

Whale populations: Mass hunting of whales has severely threatened their existence. Two events accelerated the speed at which whales were caught for commercial purposes. One was the use of the canon-fired harpoon, developed in the 1860’s. The other was the introduction in the 1920’s of ships that processed their catch at sea. So many whales were killed that some species became nearly extinct. The first protective laws were introduced in the early 1930’s. Today the International Whaling Commission (IWC), founded in 1946, regulates whaling and monitors whale populations. The IWC now prohibits commercial whaling although there is a loophole that allows killing for scientific research. Over 20,000 whales have been killed since 1985 by Japan, Korea, Norway, Iceland, and Russia. Some members of the IWC have asked for a total ban on whale harvesting although this is unlikely to happen.

Question: What animal populations are threatened in your area? What are the causes? Are there any animal populations that have become extinct in the last century? When an animal species becomes extinct, are some of the effects?

Killer Whales (Orcinus Orca):

Orca Whale Photo taken today!

Question: What do you already know about killer whales?

Some physical characteristics: Orcas are the largest member of the dolphin family. Males grow to a length between 7-9 meters and weigh between 3.8-5.5 metric tons. The female is usually 5-7.7 meters in length.

Distribution: They are found in the Southern Ocean and are common off Australia, New Zealand, Chile and South Atlantic. Some migrations have been reported but most of the population is resident in the Antarctic sea-ice.

Diet: The whales eat fish, squid, penguins, seabirds, seals and dolphins.

Social Behavior: They travel in herds of 2-50 although in the Antarctic, 50% of the pods have 5-10 animals. Pods usually have adults of both sexes, juveniles, and calves.

Breathing and Diving: Orcas breathe every 10-35 seconds during a series of short dives followed by a dive lasting 1-4 minutes. Killer whales are capable of remaining under water 17 minutes and can reach depths of 260 meters.

Humpback Whale (spyhopping) Photo taken today!	Humpback Whale Photo taken today!

Move like a cetacean: See if you can match these movements with their definitions.