I took a look at the copy of the certificate under a good magnifying glass and it could be Krelling. Someone's attempt at Crellin

I got a few second opinions and it was 50/50. I would post the piece in question but its an extremely poor copy.
William Callister son of William Callister and Amelia Crellin seems to disappear after the 1851 census so maybe he did go to Australia

Thanks for the input everyone

mab