Fish traps ... are they?

At Acairseid Thioram (Dry Harbour, in English), on the Island of Rona, betweem Skye and the Applecross peninsula, these structures were to be seen on the shoreline, between high and low tides. But what are they? Some say fish traps, others say they're far too small for that (c. 10m. x 10m., and about the same apart). Places to store kelp until needed, for the adjoining croft? Any advice greedily accepted.