Three groups of mammals have lived in the oceans for millions of years.
Whales, Porpoises and Dolphins
Cetaceans evolved from ancient land mammals, their closest living relative on land is the Hippopotamus. The group includes the dolphins and porpoises as well as the True Whales. Names can be confusing here, and the Killer Whale (Orcinus orca) for example is technically a type of dolphin. All memtbers of this group are meat-eaters, although paradoxically the enormous Blue Whale (Balaenoptera musculus) usually feeds on very small, shrimp-like,Krill.
Dugongs
Sirenians are represented by three species of Manatee (which all spend much of their time in fresh-water) and only one truly marine mammal, the Dugong. Until 1768 there was another one, Steller’s Sea Cow, but hungry fishermen hunted it to extinction. The Dugong and Manatees feed exclusively on plant material.
Maybe if you have been at sea for many months Dugongs might look a bit like young women – they are certainly thought to have given rise to the mermaid legends. The Dugong’s closest living relatives are the elephants.
(You can download a manatee video from here:http://www.sunshinerivertours.com/video1.html)
Seals
The order Pinnipedia includes all the seals, sealions and walruses. They probably evolved from bear-like ancestors and took to the sea much later than the whales and dugongs (20 million years ago as opposed to 50 million). While they are all fully sea-going most of the time they still need to come ashore to breed. Like the whales all seals are carnivorous (and very intelligent).
Sea Otters
All otters spend a lot of their time in water, but only the Sea Otter (Enhydra lutris) prefers the sea. Maybe in a few million years they will evolve into yet another fully-fledged group of marine mammal.
Big Brains
Most of the whales have very large brains, and the dolphins, certainly, are thought to be very intelligent. They seem to have some sort of language, play games even as adults, and have very complex social relationships. Different ‘pods’ of Killer Whales use widely differing styles of hunting technique – so they can be said to have local ‘customs’ and even ‘cultures’.
Conservation
On land the Giant Panda is recognised as symbolic of our need to conserve what is left of the natural world. In the oceans he is replaced by the Blue Whale. Commercial whaling drove the Blue Whale to the brink of extinction, but pressure from the general public managed to bring about legislation which has halted the decline – for the present at least.
Whale-watching is now big business, and as more and more people are able to encounter whales in the wild the number of enthusiasts increases. Hopefully concern for the marine environment will grow as more of us become aware of its complexity and the damage we are capable of causing.
(See my blog and also: 'Marine Mammal Protection Act 1972')
Other articles by John Blatchford
