The term ‘marine mammals’ refers to a variety of mammal species that rely on the marine environment for survival. All marine mammal species come from the following groups:
- Polar bears;
- sea otters;
- sea lions;
Cetaceans are an order of marine mammals, referring specifically to whales, dolphins and porpoises. There are around 88 species in total which are split between 2 suborders; mysticetes and odontocetes.
- Commonly known as whales;
- larger than odontocetes;
- baleen instead of teeth which acts like a sieve to filter food from the water column;
- paired blow hole;
- use low frequency sounds to communicate;
- migrate long distances.
- Commonly known as dolphins, but include porpoises too;
- teeth (at least 2);
- single blow hole;
- communicate with high frequency ‘whistles’ and clicks;
- do not tend to have long migration patterns;
- Biosonar/echolocation to find their prey.
It is a common misconception that species such as sperm whales or killer whales are whales, when in fact, they are dolphins!
- Cetaceans are long lived species with a life span of 18-100 years;
- they have a relatively late sexual maturity (c. 6 years);
- breeding is seasonal;
- single calf at each breeding event;
- breeding events occur every 1-4 years.
Threats to Cetaceans
Many cetaceans across the globe have a ‘vulerable’, ‘endangered’ or ‘critically endangered’ status according to the IUCN Redlist of threatened species. This means their populations are at risk of extirpation, or extinction, if population declines continue to decline at the current rate. Threats include:
- Historical hunting: dolphins and whales were hunted for their meat, blubber and baleen. Whilst whaling was banned by the International Whaling Commission in 1986, the detrimental effect this has had on their population numbers means species stocks are still depleted.
- Overfishing: prey depletion and bycatch, habitat degradation.
- Marine traffic: vessel strikes, noise pollution.
- Capture for live display in aquaria: Countries all over the world are supporting the aquarium trade.
- Marine litter: ingestion and entanglement.
It is important to keep in mind that many threats facing cetaceans are anthropogenic, with coastal populations being further at risk to the effect of anthropogenic activity.