Police in a patrol car saw the assault from a distance and it continued until officers intervened.
While handcuffed, Ryan said the tourists had assaulted them, and a co-offender, Kyle Ashman, yelled as they were being taken back to the police station, "all we need to say is that we got rolled by some English tourists".
Ashman is yet to be sentenced but he and Ryan admitted assaulting Bonnick with intent to injure.
The tourist suffered bruising to his face, a bleeding and swollen nose, split lips, sore teeth and bruised thighs.
Ryan also admitted recent charges arising from the execution of a search warrant at a Cobden house.
He was in the vicinity and was placed under arrest while trying to open the driver's door of a police car. He was drunk and abusive, trying to headbutt one officer and spitting at another.
Lawyer George Linder said Ryan accepted that his behaviour had been rude and unacceptable, and had apologised to the officer concerned.
Mr Linder submitted that a sentence of community detention was called for but Judge Kevin Phillips snapped:" No! It's home detention or prison for him."
Undeterred, Mr Linder said Ryan had a steady job and the tourist had not been seriously injured in the attack.
"How would you like bruising all over your face, split lips, a bleeding and swollen nose and sore teeth?" the judge asked the lawyer.
"These tourists were set upon by these thugs - one of them thought he was going to get thrown over the bridge.
"He was really scared when he was pushed up to the rail and heard one of the thugs say, 'put him over'.
"The female tourist had previously been mugged in South Africa. She was uneasy when she saw these men approaching, but her companions said 'it will be okay."'
Judge Phillips said it was the eighth time Ryan had been convicted of serious violence and it would be the last time he escaped a full prison sentence.
"The West Coast has developed a tourism industry which is a major player in the economy of the region.
"Drunken thugs like you destroy that industry," he told Ryan.