In the scientific community, they're called leuresthes tenuis, and this time of year they lead "tenuis" lives indeed--all for the sake of love. Swarms of California grunion, caught up in the swirl of the moonlight and the tide, hurl themselves onto beaches to lay eggs in the sand and then hurl themselves back in the sea. But then there are the grunion hunters--swarms of hands, caught up in the swirl of the moonlight and a frying pan, trying to catch the little fish for dinner. Legally, they can be snared only without benefit of nets or scoops, ensuring that a new generation will make it back to the mainland for another time. The present run continues through Thursday and the next will be June 23-26. The middle two nights of a run are best and the runs begin around 10:30 the first night and an hour later on successive nights.