Grunion

Mother Nature is impossibly creative. The most imaginative minds couldn't dream up a fish that lays its eggs on land. But that is exactly what the grunion do.

Grunion are silvery fish about 5-6 inches long that seasonally come up onto southern California beaches and lay their eggs in the sand. About twice a month from March through July, during the periods of high tide, the grunion swim toward the shore and let the waves carry them onto the beach. The female burrows deep into the sand, tail first, and lays her eggs. While she is depositing her eggs, male fishes wrap themselves around her and release their sperm "milk", which drizzles down the length of the female's body and into the hole with the eggs, fertilizing them. When the deed is done, the fish wiggle and flop back toward the ocean and the next big wave returns them to the sea. Sometimes it takes a while for the next big wave to come, but the grunion can survive on land for up to 20 minutes!

For this astounding ritual to be successful, the timing must be exquisitely precise. The grunion mysteriously know to begin spawning just after the peak of the high tide. This gives the eggs the maximum amount of time to develop undisturbed in the sand before the next high tide cycle, and it is also the time when waves deposit sand on beaches, covering the eggs with an additional protective layer of sand. Roughly two weeks later, during the beginning (pre-peak) period of the next high tide cycle, the waves draw sand away from the beach, gradually uncovering the eggs. When the fish eggs are agitated by sea water, they instantly hatch and the baby grunion are carried out to sea. The fish literally pop out of their shells instantaneously when a wave washes over them so that the very same wave sweeps them away to the ocean.

On Wednesday night, I went to the Cabrillo Marine Aquarium and took part in their "Meet the Grunion" program to witness this grand event. First, you watch a short documentary about the grunion, which is where I learned the factoids above. :) The aquarium staff then accompany you to Cabrillo Beach and help you spot the fish and explain what you're seeing. The spectacle is amazing, and I got lots of great photos, despite the fact that it was pitch dark! (This event happens very late at night: from ~10pm onward.) At times the entire length of the beach was filled with hundreds if not thousands of fish, wiggling and flopping all over the place. I could clearly identify females digging burrows, and witnessed some males wrapping themselves around the females. Once the "grunion run" (as it is called) is well underway (i.e., the momentum is strong enough that you won't scare them away anymore), you can walk right up to the fish and get as close as you want. I even peered down into one burrow and could see the orange fish eggs at the bottom. I stayed until well after midnight, watching wave after wave bring new piles of fish onto the beach. It was mesmerizing to see the fish engage in their spawning rituals with an intense purposefulness and a furious desperation to get back to the water, all too aware of their death-defying transience on land.

This was one of the most amazing exhibitions of the natural world that I have been fortunate enough to see!