Change in currents, wind direction, erosion, etc. all could be good. However, if they rake the beach and deposit the collected seaweed and stuff along with it, I would hunt the deposited piles..... I have found that when they rake a beach without seaweed, the rings are too small and fall through the grates in the hopper. But when the rings are mixed in with seaweed, they get caught up and deposited at the dump site.......