Whales and dolphins are at the top of the food chain in the ocean, which means they have few or no natural predators (depending on their size). This often means that their worst threat is caused by humans. Click on each of the threats to learn more.

bycatch
This gray whale has been entangled in lost fishing nets © B. Talbot.

This gray whale has been entangled in lost fishing nets © B. Talbot.

A serious threat to our marine friends is called bycatch and is caused by fisheries. Bycatch refers to all animals that fishermen were not planning on catching in their nets. This means that even though not many cetaceans are actively hunted these days, many get entangled in fishing nets. These animals die of injuries caused by the struggle to get free or suffocate as they aren’t able to get to the surface to breath.

overfishing

Overfishing is also an indirect threat to toothed whales and dolphins. If too much fish is taken out of the ocean by humans, not enough food is left for the natural predators of these fish, many of which are toothed whales and dolphins. Can you imagine that only 0.6% of the oceans are closed off to fishing?! This means that in biological terms, humans, taking the food of these dolphins, porpoises and whales, “outcompete” them.

noise
A 300 kg bomb exploding in the North Sea © K. Lucke

A 300 kg bomb exploding in the North Sea © K. Lucke

The noise of ship motors, sonar, military bomb testing and the construction of wind power stations or oil platforms in the sea disturbs many cetaceans, which are dependent on their sense of hearing for hunting, communication and orientation. Since sound travels much faster in the water than in the air (approximately 4 times faster) it can be heard from much further away. This means for cetaceans it is like trying to concentrate on something really important and not just hear your next door neighbor’s loud music, but an entire city filled with noise! So if animals move close to places where bombs are tested or construction takes place, the noise can be loud enough to deafen them.

Noise can also confuse animals so they get lost or stranded on beaches. It can also cause them to panic: coming up to the surface too fast causing what is often referred to as the bends (have a look at the section Adaptations to read more about it).

Chemical pollution

Chemical pollution is caused by chemicals that industry discharges into the water, oil spills, wrongfully disposed waste and stuff you might flush down the toilet that doesn’t belong there. Pollution is very dangerous because it can also affect us humans! Moreover, it is often difficult to detect chemicals and poisons, and even more difficult to clean these from our vast oceans.

Human waste
A plastic bag has wrapped itself around this dolphin’s head © N. Strüh

A plastic bag has wrapped itself around this dolphin’s head © N. Strüh

Human waste, which ends up in the oceans (accidentally or on purpose) is also known as marine litter or marine debris. Plastic bags can be mistaken for food or played with and, like in small children, be swallowed or cause them to become entangled in them, this leads to whales and dolphins being seriously harmed or dying. Even if whales, dolphins and porpoises don’t come into direct contact with marine debris and chemical pollutants, they can still be severely affected by it.

Did you know that whales which are washed up on the beach may have suffered from so much contamination with poisonous materials that they must be treated as hazardous waste?

Climate change

Climate change caused by humans has resulted in planet Earth getting gradually warmer since the industrial revolution. Us humans have shaped nature in many ways and interfered with natural cycles without knowing what the consequences were. Today, we know that the climate of our planet is changing because of these interferences. This means that the global temperatures are rising, the weather is changing, and natural disasters, such as hurricanes are likely to happen more often. There is an added possibility that ocean currents, which influence regional climate patterns, may alter their paths. With climate change, the oceans are also getting warmer; this changes the environment of marine animals and the amount of food they can find. As a result of this, they are forced to either adapt to the temperature change or migrate in order to cope with these changes. Those who cannot cope are faced with extinction. There is no way to reverse climate change, only the possibility to slow it down and keep it to a minimum.

destruction of habitats

The destruction of habitats (the place where an animal lives) is problematic because it often affects more than one species and is hard to reverse. Imagine a rain forest: if all trees are felled, most animals that live there will lose their home, and it will take decades or centuries for new trees to grow back. The same can happen underwater and no one knows if such places can ever be repopulated by the original animal. As with pollution, habitat destruction is also a danger to us because it changes the cycles of nature. Habitat destruction has been linked to the occurrences of acid rain, algae blooms and the loss of young fish (who often depend on coastal nursery grounds) to happen more often. In fact, some evidence suggests that habitat destruction contributes to global warming.

Big ships
A whale that has been hit by a big vessel © F. Félix

A whale that has been hit by a big vessel © F. Félix

The presence of humans in cetacean habitats can have many other effects too. Big ships can directly strike the animals or they can be hurt by the ships’ propellers, this often leads to life threatening injuries.

hunting

The oldest and best-known threat to whales and dolphins is hunting. Many communities have a long tradition of hunting cetaceans, with the oldest evidence of whaling tools; archaeologists found being over 5,000 years old! For much of our human history, whale hunting was sustainable and posed no big threat to populations of cetaceans since it was a lot of hard work and dangerous for humans to kill a whale. However, in the 18th century, the European population began to grow very fast: people needed oil from whale blubber and the number of whales hunted began to increase. Meanwhile, European whalers believed that the supply of whales in the ocean was endless and didn’t realize they were killing too many. This continued in the early 20th century, when people began to realize that many of these whale species were close to extinction.
Since then, international conservation efforts have focused on stopping whaling and protecting the remaining few animals. One of the most important organizations doing so is the International Whaling Commission, which regulates all whaling activities. They decide which species are placed under strict protection, and how many animals are allowed to be hunted. Sadly even today, after 60 years of protection, no population has regained its original size and many are still in danger of extinction. Many people today believe that all products which originally came from whales have been replaced by other sources and so there is no need to hunt anymore whales. As a result of this whaling is often seen as a very controversial topic.

whale or dolphin watching

Even seemingly harmless activities, such as whale or dolphin watching can be a problem to the animals. Boats and large groups of people stress the animals and can disturb their time for resting, feeding and playing with each other. In extreme cases it can even cause whole or pods to become separated from each other. This can also make the animals become aggressive towards humans.