You decide to row back to the shore and knock politely on the doors of the 5 shacks until you find someone who would give some kelp.
Back at the shore you walk up to the first house and lightly knock on the door. You don't know what to expect, or what you are going to ask, or how you are going to get kelp even if anyone has any, but you figure its the best idea you have.
You hear no answer, and no lights or noise from the other side of the door.
You knock a bit louder.
Still no answer.
You knock a bit louder.
The door creaks open a little. You peek inside.
At first you cannot see anything, as your eyes have not adjusted to the dark, but slowly you start to see the outlines of shapes. The first thing you see is a broken wooden table in the middle of the room. There is a cracked plate on the ground, some clams and a fish on the floor. In the corner is a shelf with some books that appear to have been torn up, and in the other corner is a bed, with the sheets all thrown about.
Oh yeah, and on the floor of the shack lies a giant dead otter. It has a dagger sticking out of its chest.
You look at it for a few minutes, not sure what to do. You look around the room, and find there is no kelp. Sigh. Next house.
You walk over to house number 2. This time you decide not to knock. If someone is there, they may think you killed the otter in the last house. Instead you roll for walk quietly and hide. Luck! You roll a 24. You are just glad you used dexterity as a dump stat.
You quietly crack the door open and look around. Guess what you see?
Yep. The same thing as the last house, but the dead otter is dressed differently, and sitting slouched in a chair with a dagger in it's back. You are starting to see a pattern.
You check the other 2 smaller houses and see a similar situation. You turn to the larger house, the one that had smoke coming out of it earlier. There is no smoke, nor light, now.
You quietly open the door to this shack, looking in. In the middle of this shack you see a large black cauldron with a strange, grotesque face carved on the front of it. Around the cauldron are 5 fur pelts. 4 of the pelts are stained with blood. One is clean. Again, no kelp. Walking back outside the shack you notice via the moonlight another pair of footprints in the sand, much smaller than yours, who look more like an animal than your converse prints.
You start to consider what you have seen, and inductively try to determine what happened here, a la Sherlock Holmes.
All you can guess is that whomever killed those poor otters stole all the kelp too.
You decide to come up with a new plan. You could follow the footprints, or you could row back out to sea and use the fishing pole and net to hopefully catch some kelp. Or you could just skip the kelp and chant for the sea witch without kelp.