Not all dolphin experts thought the two men convicted of disturbing Dave the Dolphin had actually caused the animal any distress.

Dr Horace Dobbs, founder of International Dolphin Watch who has studied dolphins for 45 years, said dolphins like to play and some solitary dolphins seek out and enjoy human contact.

Michael Jukes and Daniel Buck, both of Folkestone, were found guilty by Dover Magistrates of intentionally or recklessly disturbing a wild dolphin at Seabrook, near Folkestone, in June last year. The men, both 26, said they were only having fun after getting drunk at an all-night party.

Four experts told the court the female bottle-nosed dolphin was showing signs of distress. But Dr Dobbs, who has conducted studies of how swimming with dolphins can benefit clinically depressed people, told the court Dave would have enjoyed his encounter with the two men.

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He said dolphins are playful creatures. "They indulge in play a lot of the time ," he said. "They have time on their hands - or their fins. I have seen dolphins playing with a sea cucumber as if playing rugby."

Dr Dobbs, a witness for the defence, said Dave would have been "the master of the situation" with the two men and would have swam away if she was not happy.

The expert said dolphins like Dave look for experiences to stimulate them. He compared them to people who want to run marathons or climb Everest. He said they were not unnatural, but unusual.

"The dolphin was looking for humans. They liked to be stroked and touched. They are tactile animals," he said.

Dr Dobbs has given lectures about dolphins all over the world, including at Oxford and Cambridge universities.