Presumably one may exclaim this when an oyster is cracked open "shucked" to reveal a pearl within its manky outter shell. In the similar fashion "eureka" was yelled when someone found gold, so that everyone in the area knew where to run towards, most likely to shoot the proclaimer, and pinch the gold nugget.
Someone tells a joke. The crowd laughs. "that was a pearler" someone exclaims.
Someone gets a flat Tyre or puncture. The sidewall is absolutely fucked. "Oh thats a pearler there. buddy"
Aw mate have you tried beer chicken?
Na what's that?
You stick a can of beer up the chooks arse before it goes on the Barbie tastes bloody lovely!
Dead set? Pearler mate ill give it a go then eh