Now I am not, nor desire to be, expert on these type of matters but from wikipedia it appears that this dukedom is reserved for the Royals and, as matters stand today, has never been awarded by itself per se, but rather in combination with another. Including Cumberland it appears.
Perthshire's Strathearn, or valley of the Irish, too is known for it's glass, Teachers whisky rebranding the popular Vasart company set up by Salvador Ysart in 1947. The Strathearn Glass logo was a leaping salmon whilst Teachers sold out to Stuart Glass in 1980 and the company was again rebranded, this time to Stuart Strathearn. Production ended in 1992.
Perhaps there is esoteric wisdom to be taught here in terms of the salmon, the king of fish - who leaves it's home-burn and travels down to the sea to migrate in search of rich food. It then returns - an arduous journey - to spawn, before, hopefully making the journey once again.
wiki - Duke of Strathearn.