Both the Canadian built ships were built for Canadian Offshore Marine so were part of Offshore Marine - they were not chartered in.
1968 saw the founding of the marketing company for supply ships, the Offshore Supply Association (OSA) Ltd in London. Member comopanies were:
NordseeVersorgungsschiffahrt G.m.b.H., Hamburg,
Deutsche Dampfschifffahrts-Gesellschaft "Hansa", Bremen
Offshore Marine Ltd., Great Yarmouth.
Offshore Marine ships were managed by the International Offshore Services (UK) Ltd., London, until 1968. Hays Wharf being a part of London and Rochester Trading. If you look at the history of the South Shore, as built she carries the funnel markings of that company (L&R Trading) but was managed by IOS under the Offshore Marine tradename - however, she always carried OSA funnel markings (and number) when Hays sold to Cunard (who allied to OSA!)
On April 1, 1968 Offshore Marine Ltd. was sold by Hay's Wharf Ltd. to Cunard.
Both the Scotian Shore and Breton Shore were 'OSA numbered' (552 and 553) and built for the Offshore Supply Association - of which OM was a partner. From the start they wore Offshore Marine co,lours and funnel markings and flew the OM houseflag. They are also included in fleet lists for OM.
On December 31, 1972 Offshore Marine Ltd. separated from OSA. However, ships with OSA numbers in Offshore Marine retained them but not on the hulls are the OSA ships did. An example is that the Channel Shore, as built, carries the OSA roundel on her funnels with the OSA number 504. She was UK flagged and registered and had a UK callsign GQET. Later in '72 she took up OM markings.
The histories of the Breton Shore and Scotian Shore are as follows:
Breton Shore was sold in 1980 to Geophoto Services of Pictou, Canada and became the Edward O Vetter. In 1995, Secunda Marine bought her and she became the Cabot Sea. In 2005 she became the Oceanus 1for an undisclosed Panamanian owner before being bought by Mabisel Trading of Nigeria and staying with them until 2010. She is listed in Equasis as survey overdue but also known to be out of service. I do not know where she is currently.
The Scotian Shore became the Fred G Agnich of Geophoto on sale in 1980. In 1994 she was sold to Western Sea Service of Panama and became their Western Crest until 1995 when, with the same name, she was sold on to an undisclosed Panamanian source before going on to Maritime Atlantic of Kingstown in 1996, and became the Western Salvor.
In 1997 she reverted back to Scotian Shore and was sold on to Tuna Suppliers of Kingstown. IN 2006, still as Scotian Shore, she went on to Freeway Marine for a short while before being sold on to Petra Services of Piraeus. In 2010 Equasis had her as no longer in service and this was due to - possibly - certification issues. She has been detained under Paris IMO several times.
I hope that helps?
Jonty