Not as many Sea Urchin’s on the sand

As a former "Urchin Diver" from BC, maybe I can enlighten you, DaveJ. If you spear them, they will die. They are on the sand for only a very short time. Both the males and females release gametes into the water where they produce fertilized eggs which eventually settle out and attach them selves to a rocky substrate. This substrate is normally where urchins live. Leave them alone!