Above is a closeup of one of the walls. I took this info off the Still Bay Information Brochure: The seaward side slopes gently to make it easy for the fish to swim into the trap. The internal face is vertical and clear of debris and silt, so the “vywers” can be drained quickly and trap the fish as the tide recedes.
Below is a photograph of the brochure given out at the information office detailing the names of people who “own” the fish traps. Most of them are a half moon shape and vary in size and from what I could gather, some are better at catching fish than others. Nowadays, sadly, fish are scarce.