Thanks to Joanna Klein and the Science section of the New York Times for this explanation of a full moon mating phenomenon:
Every year, thousands of little fish ride waves onto Southern California’s beaches at night to lay and fertilize eggs. High up in the sand, they squirm, wriggle and wrap around one another. As they dance beneath the moonlight, the beach transforms into a twinkling tapestry of spawning silver bodies. It’s known as the grunion run, and within a few hours, the show is over.
This spectacular reproductive event occurs twice a month on nights after new and full moons, when tides are at their highest. The show, which plays out on West Coast beaches from Baja California, Mexico, up to San Francisco Bay, peaks between April and May, but can last from late February through August. With Tuesday’s full moon just past, now is the perfect time for a grunion run, if you happen to be in the area.
“There’s a lot of chaos going on,” said Karen Lynn Martin, a biologist at Pepperdine University who specializes in grunion. “It’s pretty amazing.”
Once the female gets to shore, she twists her body, tail first, into the sand about two inches down and lays up to 2,000 or 3,000 eggs. Then the male wraps his body around hers, spraying sperm-laden milt that fertilizes the eggs. When it’s all done, the adult fish catch a wave back out to sea, leaving their eggs behind to incubate under the sand until the next big tide rolls in…