Last night I was gazing at the full moon, as is my wont, and started thinking about werewolves, as is my wont, and wondering if the full moon really has any effect on human body chemistry. Thousands of years of mythology say yes, science says no. I wondered, then, where the myth might have come from; surely the full moon has an effect on something in nature? Ah, yes, I thought. The tides. And then I recalled a plain-looking little silver fish with a very ugly-sounding name.
You probably know that the tide is highest when your part of the Earth is closest to the moon, due to its gravitational pull. Why, then, are there two high tides every day? Simply put, the tide is high when you are 180 degrees from the moon, because then the moon’s pull on the Earth is greater than its pull on the water where you are. It’s not so much that the tide is high; it’s that the Earth is low. Hence, the ocean is slightly oval-shaped on top of the Earth’s sphere, with its highest points being nearest and furthest from the moon, and its narrowest points on the sides — the low tides.
What’s more, there are different types of high and low tides, depending on the moon’s phase, which depends on where it is, relative to us. When the moon is new, it is right between the Earth and the sun, a monthly phenomenon known as syzygy. The sun adds its gravitational pull to the moon’s, creating super-high tides known as spring tides. When the moon is at a quarter or three-quarters, the sun’s pull works against the moon’s pull, creating weak, super-low tides called neap tides. When the moon is full, it’s on the other side of the Earth from the sun and creates another spring tide, albeit not as strong as the new moon’s. It’s a little more complicated than this, but I’m not a physicist and you’re not a sailor.
Which brings us to today’s animal: The Grunion.
Outwardly, it’s not the world’s most interesting fish. It’s small. It’s silver. It’s pretty much dolphin bait. But when the moon is full (or new), when the tides are highest, a hormone change sends the grunions in California rushing the beaches by the millions, all trying to simultaneously spawn and lay their eggs at the highest point on the beach. During a “grunion run,” it seems as though the ocean has become mercury, with all the silver fish fighting to surf the waves furthest onto the shore. The female buries her tail in the beach, and up to eight males will try to spill their seed on the eggs she buries four inches in the sand, all within about thirty seconds. The spectacle is literally a lunatic orgy.
Why this bizarre moon-inspired sex ritual? After all, laying their eggs on land makes them literally fish out of water, an all-you-can-eat buffet for herons, raccoons, coyotes, and Californians, who, in what seems like the most fun form of fishing ever (and grossest, unless you really love wading into fish sperm), are allowed to keep anything they can catch with their bare hands. And the buried eggs aren’t safe, either, making a delicious breakfast for probing seabirds. But there are so damn many grunion that no amount of predators could collect all of them, or find all their eggs. And laying them at the highest point on the beach during spring tide, where the water will not reach them until the next full or new moon, means they are safe from predation by other fish… which is apparently worth it. And grunion eggs laid during the full moon will remain out of reach from those aquatic predators until the new moon, when they will hatch and venture out to sea on the high tide.
So, the morals of the story are:
1. For the grunion, sex with multiple partners is the safest sex.
2. Many animals, particularly ocean-dwellers, use a lunar calendar to ensure the survival of their species.
3. If the full moon ever triggers an intense hormonal desire in you to fuck like crazy, you’re not alone.