When I was growing up on the Isles of Scilly I remember Canadian flags being flown for a while. I vaguely remembered that they were disputing Spain’s fishing policies, and that English fisherman were also opposing Spanish practices.
The actual dispute between the two nations occurred in 1995 and regarded alledged over-fishing of halibut by the Spanish in protected international waters. Canadian authorities, however, went outside of their waters to seize the Spanish fishing trawler Estai. The IHT explains.
I believe locals were opposing Spain because of limitations for the Irish and British fishing in the Irish Box, whilst Spain demanded greater access to fishing there.