All down the west coast of Ireland they have found fish traps in tidal shallow water. These were made of wicker-like panels arranged to make a funnel, which (I believe) led into an enclosure. These are only around 1000 years old, but wood in water ain't a good laster so no one knows how old the practice is. If they could produce something as amazingly longlived as the curragh they could surely come up with oyster beds and fish traps.