You’ve lived a life on the coastline, working above and below water, and benefited from your natural adaptation to the aquatic elements.
BENEFIT
You take no penalty to Acrobatics on ships in rough water, and only a -2 penalty in stormy waters. The DC for swimming in rough and stormy water is reduced by 5. You can hold your breath underwater for an additional number of rounds equal to your Constitution modifier.
Normal: Rough waters incur a -2 penalty to acrobatics, and stormy waters incur a -5 penalty. The DC for swimming through rough waters is 15, and through stormy waters is 20. You can hold your breath underwater for a number of rounds equal to twice your Constitution.