When I was a kid (60's) they always seemed to be called Schnapper. I remember a book on fishes that we had dated right back to the "olden days" and that called them schnapper, mind you, Bluefin Tuna were Tunny fish in that book back then. 

Scnapper Rock is the name that you see on maps and stuff ... not Snapper Rock. Nowadays not many call them schnapper, but then it is harder to spell..

I always thought that snapper was an american term, they like to be different. There are so many types of fish called snappper but I think our snapper was originally a schnapper and we just got lazier. Sort of like programme and program.

This site refers to  the word schnapper or snapper...

http://www.bartleby.com/61/85/S0138550.html

“Snapper” is a generic name for hundreds of snapper fish-species around the World.

For some reason, the spelling schnapper crept into the Australian and New Zealand vernacular in the 1840s era, quite likely because the local caught snapper was different to those in other waters and this colloquial variation became the way to describe the Australasian species, whose scientific name is Chrysophrys auratus - auratus referring to the reflective coppery-pink colouring. The schnapper spelling is historically permanent when used for Australasian place names, utilised on coastlines, for streets and even a suburb in Auckland.

As a word-count exercise to determine spelling-use from the 1840s, the NZ PapersPast website reveals word-use scores:- Snapper 4671 to 11940 Schnapper in articles, and, Snapper 1804 to 19051 Schnapper in advertising - so in the public arena the schnapper spelling is an established and popular preference, notably by 10 times within commerce, NZ fishmongers advertising having a clear preference to using schnapper in their windows, alongside fillets of stingaree in older times.

Even scientists at MAF referred to schnapper at times, as when tagging fish at sea for research purposes in the 1980s, and some newspaper editions in NZ continue today to utilise schnapper.

It is suggested in circles, that schnapper should be used more often as it is a local aberration that should be embraced to describe this Southern Ocean fish, with the purists and prescriptivists left to argue bitterly in a corner of some fisherman's bar.

Can one conclude then that snapper is the lazy way to spell schnapper?