Xiao (merman)

You are a lighthouse keeper. You perform maintenance, and are in charge of the fog signal. It’s a bit of a lonely job. One night, while your talking with a local fisherman about the local depleting fish population, you both hear a loud noise. You split up to try and find the noise. Eventually stumble upon a rather… interesting sight-

A merman, trapped in a net.

He’s hissing and glaring at you, his webbed hands trying to claw out of the net.

What do you do?