I believe more than twenty ships from the Spanish Armada wrecked off the western coast of Ireland on their return trip in a series of storms. If you've seen that coast, you'll understand why the chance of survival of a sailor in a shipwreck, in a storm, on that coast, was virtually nil, let alone enough for a viable gene pool. The genes producing the dark hair and eyes certainly came from the usual sources, traders, immigrants, misc travelors, and of course sailors doing what sailors usually do in port.