Perth had a breeding group. Like many of their primates, the zoo decided to excise them from the colllection and shipped them out - in this case to Gorge where there are still a few old individuals remaining from the group (I think just three now).
Not sure when - @tetrapod would probably know - but probably early 2000s.
@Ashanti@Chlidonias hey yeah in January 1999 they were still at Perth Zoo but when I returned in September 1999 they were gone so definitely mid '99 they would have gone to Gorge.