I remember a Bob Hope war comedy. The supply ship with the beer goes down, Hope figures out the currents, and finds a cove full of beer cans.
Perhaps a cannery ship went down off the coast, and Damian's father "caught" such cans of salmon before the tide change?
Either that, or the father actually did the home canning thing - pressure cooking Ball jars of the salmon he caught.
That’s how my dad canned salmon: a steamcanner on the stove, and the kitchen table full of Mason jars.