To find the difference, we need to subtract the height of the fish from the height of the bird. If we use sea level as 0, then the bird flies at 1,281 feet, and the fish swims at -282 feet.
1,281 - (-282) = 1,281 + 282 = 1,563 feet
There is a 1,563 feet difference between the height of the bird and the depth of the fish