I catch mackerel all year long and throw 90% of it back.
I personally can't eat King Mackerel, some Spanish Mackerel is ok if cooked the same day as it is caught and Cero is actually getting close to edible but King is just a big no-no for me. Lot's of people eat it, I am just not one of them.
I can't imagine what Mackerel in a can would taste like. God Bless you for going with it! If it wasn't so far to Oz I would overnight you some on ice next time I caught it.
Here is my sons first King Mack he caught by himself, this picture was from 12/2005.
What we think, or what we know, or what we believe, is in the end, of little consequence. The only thing of consequence is what we do. -John Ruskin