What are marine/aquatic mammals?
A group of animals that is adapted to a life either entirely or partially at sea/freshwater environments. They are warm-blooded, breathe air through lungs, give birth to live young and nurse their young with milk (maternal care).
What are the types of marine/aquatic mammals?
There are 5 groups in this world:
Cetaceans (whales, dolphins, porpoises)
Pinnipeds (seals, sea lions, walruses)
Sirenians (dugongs, manatees)
Globally, there are:
88 species of cetaceans (1 extinct)
34 species of pinnipeds (2 extinct)
5 species of sirenians (1 extinct)
3 species of sea otters
1 species of polar bear
For a complete listing of all species of marine/aquatic mammals in the world, please visit this link at the Society of Marine Mammalogy’s website.
Where are marine/aquatic mammals found?
Marine mammals are found in the following habitats around the world:
Open sea – continental shelf waters & deep waters
In tropical, subtropical, temperate and cold waters
Aquatic mammals are found in the following habitats around the world:
Inland lakes (e.g. Lake Baikal, Siberia)
How do marine/aquatic mammals keep warm in the water?
These animals have a layer of fat called blubber that helps to keep them warm. Tropical species have a thinner layer of blubber compared to species that inhabit temperate and cold waters.
In the cetacean group, how are whales, dolphins and porpoises different from each other?
There are 2 groups of whales:
Baleen whales are the larger species of cetaceans and have a physical characteristic in their upper and lower jaws known as baleen plates to facilitate their filter-feeding behaviour. Baleen plates are made up of keratin, just like our nails and hair!
Toothed whales include whales, dolphins and porpoises. All toothed whales, as their name suggests, have teeth and do not filter-feed. (Mind boggler: All dolphins are whales but not all whales are dolphins!)
Dolphins are a non-technical, common term used for smaller toothed whales and have conical-shaped teeth. Most species of dolphins have falcate (curved) and pointed dorsal fins, however, some species have rounded dorsal fins (e.g. Hector’s dolphin, Commerson’s dolphin, Irrawaddy dolphin)
Porpoises are toothed whales that are much smaller in size (not more than 2.5 meters in body length) and either have short beaks or no beak at all (rounded head). Unlike dolphins, they have flattened, spade-shaped teeth. Their dorsal fins are also typically small and more triangular in shape.
What do cetaceans typically eat?
The diet of these mammals are species-specific. However, in general:
Baleen whales – krill, plankton, small fishes (e.g. anchovies)
Toothed whales – fish, squid, prawns, crabs, large marine snails
Porpoises – prawns, fish, squid, crustaceans
What are the current threats to cetaceans?
All over the world, cetaceans are threatened by the following:
Entanglement in fishing gear
Habitat degradation from development activities
Large-scale and small-scale pollution
Depletion in prey resources
Collision with ships and other marine vessels
Seismic exploration activities