Cook's Note: all ingredients should be as cold as possible.
In a blender combine the egg whites, scallops, and salt and pepper, to taste. Blend until a puree is formed, then slowly add the heavy cream. When thoroughly mixed, pour into a metal bowl and put over a bowl of ice water.
Add the shrimp, sea bass and salmon to the scallop mixture and gently fold to combine.
Cook's Note: At this point you can do a test with the finished mixture by bringing a small saucepan of water to a boil over medium heat and adding a small amount of the mixture. Reduce the heat and simmer until the mixture floats to the top. Cool it in a bowl of ice water and taste. This will tell you if you've seasoned it correctly before you stuff the mixture into the casings.
Stuff the seafood mixture into the pork casing, and tie into 4-inch links. In a medium saucepan, bring the fish stock or water to a simmer over low heat. Add the links and poach gently until cooked through.
In a large skillet, over medium heat, heat the oil, then add the red onion and cook until translucent. Add the sauerkraut and mustard and cook for 4 minutes, then add the chopped tarragon.
To serve, add a little sauerkraut to each plate and top with 2 seafood hot dogs.