In a small saucepan over medium heat, simmer the balsamic vinegar until it is reduced to just about half the amount. Add the blueberries and maple syrup. Simmer until the blueberries begin to burst, cooking for a minute or two. Remove from heat and add a pat of butter and stir until combined. Cover and set sauce aside if using immediately.
Pat the salmon dry and in a grill pan or on a grill at medium-high heat. Cook skin side down for 3-4 minutes. Timing depends on the salmon's thickness and the grill's heat.
Flip the salmon over and cook for 1-2 minutes or until desired temperature/doneness.
Remove the salmon from the grill and top with a spoonful or two of the savory blueberry sauce.