I agree that the BG will spawn without making these. However the success of spawning will improve with gravel and just as importantly you will encourage them to spawn where you want them (so you know where to watch and fish).
I would make this on top of the island and down the point. I would use rock (not pea gravel) and no sand and make the impression with the back of a shovel. Then add about a half shovel of rock per bed.








This is a RES but gives an idea of what a bed should look like