Desperately Seeking John

A couple of months ago, I found out via an 1896 newspaper article that my ancestor, Alexander Ritchie BUCHAN, had a brother called John.  John was there when Alex died pulling in a fishing net but where was he all those other years?

18 foot shark caught in Otago Harbour 1894

Charles BUCHAN and his wife Jessie (Janet RITCHIE) migrated to New Zealand on the Rimutaka in 1893. All their children (except Charles), some of whom had begun their own families went too.  Peter, Jessie (married to John BUCHAN), Alex and William all arrived on the Rimutaka. John had never appeared with the family on the censuses and so I hadn't realised he was missing.

A little bit of research proved that John was actually twin brother of William - born 11th July 1868 in Peterhead.  Was it just coincidence that he was away from home all those census nights?  Did he stay in Scotland or

A search of shipping lists from 1890 don't seem to show John's arrival in New Zealand so it seems likely that he migrated before the rest of the family.

RMS Rimutaka

A search of the IGI comes up with  9 other John BUCHANs born in Scotland in 1868 alone. I have scribbled down these parents names to avoid confusion as the long census search begins...

Edited to add:
Just reread an excerpt from Roy BUCHANs book about the family:

The Buchan family settled in Carey's Bay, a mile from Port Chalmers. They fished in the comparative calm of the inner Otago Harbour instead of the hazardous and stormy North Sea. The main breadwinners were Jack, his brother-in-law Alexander and father-in-law Dade [Charles]. The younger two men would fish from an open boat in the harbour and Dade would sell the fish.

Could brother John actually refer to his brother-in-law John (married to Jessie)? The newspaper article mentions that Charles also gave evidence at the hearing which means he was probably also there (as the excerpt suggests).