Yes, these are simply tidal fish traps. there are more along the west coast at a different orientation.
they are modern, as in they are currently in use by local fishermen from the coastal villages, but ancient and traditional in design, simply wooden stakes driven into the sand-bed and the suspended nets form a funnel that fish can swim into but not out of.

As for the lines, they seem to be just natural rifts or channels in the bed.
This water is very shallow, possibly less than 4 feet at low tide.