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For years humans have wondered what the high pitched noises made by dolphins and whales mean.

And now scientists believe that the marine animals squeal with delight to express their happiness.

Initially, noises emitted by the animals when offered fish treats were thought to be signals communicating the presence of food.

Scientists believe that dolphins (stock image) and beluga whales squeal with delight to express their happiness.Initially, noises emitted by the animals when offered fish treats were thought to be signals communicating the presence of food

Whales and dolphins are known to squeal when they hear a whistle or buzzer associated with a food reward.

But when dolphins and beluga whales were trained to switch off a sound after making a deep dive, they announced a successful mission by producing the same squeals.

It was the equivalent of a human 'whoop' of triumph, according to U.S. cetacean expert and author Dr Sam Ridgway.

'The [squealing] behaviour had transferred over to another stimulus that wasn't food,' he said.

To investigate further, Dr Ridgway and his colleagues at the National Marine Mammal Foundation in San Diego, California, analysed decades of recordings of experiments involving dolphins and beluga whales.

Beluga whales (pictured) also squealed to signify happiness in the experiment. Dr Ridgway said: 'We think we have demonstrated that it [the victory squeal] has emotional content.'

They wanted to understand if the delay before a squeal was mirrored by the release of dopamine, a brain chemical that stimulates sensations of pleasure.

Dopamine release takes 100 milliseconds, so if the delay between a reward promise and a squeal was longer than this amount of time it would suggest a connection.

In dolphins, the delay was 151 milliseconds and in beluga whales 250 milliseconds.

'We think we have demonstrated that it [the victory squeal] has emotional content,' said Dr Ridgway, whose findings appear in the Journal of Experimental Biology. 

Male dolphins have been known to show their romantic side by presenting their partner with a specially-selected piece of seaweed, which if she accepts, can lead to a relationship and mating