For hundreds of years whales, dolphins and porpoise (also known as cetations) have been in danger of their worst predator - HUMANS!. They have been hunted for their blubber, oil and meat.
Drive fishing in Japan, where entire schools of dolphin are driven close to shore and killed for their meat, is a serious threat - thousands can be killed annually.
The world is a rapidly changing place and even the remotest places, such as the high seas, can be affected from the negative impacts human activity.
Environmental Pollution: One of the greatest threats to dolphins (and
other marine animals) is the contamination of the marine environment- their
home. Pesticides, heavy metals, plastic particles, radioisotopes and other
industrial wastes are released into our oceans, bays and rivers. The
toxins are absorbed and accumulate in organisms that the dolphins feed on. The
toxins are absorbed by the dolphin body, which is thought to lower the
dolphin's reproductive success and may weaken their immune system, making them
more likely to get sick from disease.
Noise Pollution: Dolphins have a strong reliance on sound for communication, navigation and
finding their prey. Humans commercial, recreational and industrial activities at
sea have all expanded greatly contributing to a great increase in the
overall levels of noise in the oceans. This 'noise pollution' can overlay
sounds of importance, potentially resulting in changes in breathing rate,
surfacing activity or dive times, changing direction or moving away from the
noise source. This can interrupt normal communications and
may cause long-term abandonment of an area important to dolphins, for example
for feeding, breeding or resting.
Sharks are also a common predator of the dolphin. Many adult dolphins have scars or scratches from being attacked or injured by sharks. Some male dolphins will head - butt or try to push the shark away, wile trying to defend themselves, their family or territory.
Other threats to the dolphin population include:
 | Habitat loss |
| Entanglement in fishing nets |
| Human disturbance |
| Prey depletion (lack of food) |
| Industry and environmental changes |
Bibliography:
Habitat degredation. http://www.earthtrust.org/wlcurric/dolphins.html
Parish, S. Amazing Facts about Australian Mammals. Discover and learn vol.2. Steve Parish Publishing, 1997.