Look to me like it might be boats running in a circle to capture fish in a gill net or purse seine. I suggest this because they all appear to be in
shallow water. Gill nets don't work in deep water because the fish can escape by diving downward out of the net. In shallow water, weights along the
lower portion of the net keep it in contact with the bottom.
That doesn't look like any boat I've seen and I've lived by the sea 99.9% of my life and worked maritime security. Plus, in the OP's image there are
only 2 of these circles, one in the shallows, one in deeper water near the tip left of the image.
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