He's a special character. When you dive in the water and catch an Scallop, he will pop up and ask for it in exchange for a piece of rare pirate furniture xP.
Haha pretty much! Pascal is a special character you see in the ocean when you deep sea and grab a scallop. If you give your scallop to him, he'll give you an item and tell you some....interesting quotes.
I just realized my post ordered Pascal sightings from daytime to nighttime. That was unintended but neat. As shown in the pictures though, you can see him any time of the day and any part of the ocean as long as he has space to appear and you catch a scallop.