Hi dave..
A very fine reminder of catching a great predator, and on your new rod, wouldnt worry to much mate, like Graham says, with the dirt, sweat, and other things that are going to get on it in later years, the old blood will slowly vanish, bit of cold water and a rub should get the surface matter off, but yeah cork naturally absorbs so there isnt a heck of a lot you can do, but the sooner it was washed off, the better, the later marks will go with time mate.