How do humans harm dolphins?
Dolphins of course suffer natural threats such as natural disease and shark attacks. Sadly, the main threat to dolphins comes from human beings.
One of the main threats to dolphins is from commercial tuna fishing.
Spotted, Spinner and Common dolphins in particular often 'school' above yellowfin tuna in the Eastern Tropical Pacific. Strangely, it seems that the tuna follow the dolphins, rather than the other way round. As a result, tuna boats set nets around schools of dolphins, knowing that where there are dolphins, they will find tuna. Tuna boats then use speedboats, helicopters and small explosives to herd dolphins into purse seine nets which can be up to one mile wide. Stuck in the nets, the dolphins then die. Tens of thousands of dolphins have died in this way.
If you eat tuna, always make sure it is from a dolphin friendly source.
Pollution: Pollution can be very harmful for dolphins, especially river dolphins in the Amazon, Ganges and Yangtze where chemicals and sewage can concentrate in dolphins because they are at the top of the foodchain.
Garbage such as plastic bags and bits of plastic can build up in the sea and present a danger to marine mammals such as dolphins. These are sometimes so large they are described as islands of garbage.
Boat traffic: Ship and boat traffic can also cause injuries to dolphins either from propeller blades, or lines and other obstacles in the water.
Noise: Noise travels far further in water than in air. Oil drilling, navigational sonars and ship engines can all frighten, disorient and confuse dolphins. Noise pollution may cause marine mammals to beach themselves and may also force dolphins to move away from their normal feeding and breeding grounds.
Hunting: In some cultures it is traditional to hunt dolphins and whales. This still takes place to a limited extent in the Faroe Islands, Iceland and Japan.
Tourism and dolphins: Many humans want to get close to dolphins. Dolphin-watching boats need to be careful not to approach dolphins too closely. Intrusive tourist boats can disrupt dolphins and other marine mammals and scatter groups which may be especially harmful to females with young calves.
If dolphins are fed by humans, they can become dependent on hand-outs rather than hunting for themselves. Dolphins that approach boats for food are often more vulnerable to injury from engine propellers, fishing gear and so on.
If you want to get close to dolphins, always make sure that you do so with a responsible operator.
Rarer species of dolphins may be threatened when climate change disrupts currents or their sources of food.
Read more at the Dolphin Institute.