My observations are that its generally larger females that go tar spot/berried in the shallows. Often all the larger females on a patch of reef go tarspot/berried at the same time. I think these are more resident crays rather than those that participate in the whites run. 

Over the past two weekends I've noticed quite a few crays right up in the shallows that seem to be in the process of breaking down their old shells. They go a bit slimy and their shells become soft/brittle I interpret this as them secreting some enzyme or something that breaks down the shell in preparation for them to shed. Then they'll hang out in the shallows hiding and waiting for their new shell to harden prior to starting the walk. I have no idea how long it would take to break down an old shell and harden up the fresh one - seems like people reckon the walk will start in about two weeks time though - will be interesting to see.

BTW this is all speculation and observation. 

 Thanks. What I saw today was consistent with what you said about all the females going tarspot/berried at the same time. I think last year people were hoping for a November whites run, but it didn't seem to get going until about one week into December.  So about a month after the full moon on 8th November. Not sure if the moon phase triggers the run, but this year the November full moon is 28th, almost 3 weeks later than last year. So I'm thinking if the run is the same as last year it could be end of November, around 28th,  or late December, which seems too late. But I'm a beginner, so no idea...