The best thing I fund is to let your health get as low as possible before healing. Im talking around below 20 or 20. That way, you will conserver them.
Also, use the move where you impale them on your spear and then launch them into the air, then cut them in half with the disc while they fly. Very quick way of disposing them. And obviously execute whenever possible.
And obviously manually kill them with spear gun from a distance whenever you can.