"Along Southern California's sandy beaches, from March through September, one of the most remarkable life cycles in the sea is completed: the California grunion come ashore to spawn. The grunion has been known to many Southern Californians for more than 100 years, but there are still those who are skeptical of its existence. To be invited out in the middle of the night to go and watch fish does sound a little ridiculous, but in reality this is the only way to observe this natural phenomenon.

California grunion are small, silvery fish found only along the coast of Southern California and northern Baja California. Most people would be unaware of their existence were it not for the unique spawning behavior of these fish. Unlike other fish, grunion come completely out of the water to lay their eggs in the wet sand of the beach. As if this behavior were not strange enough, grunion make these excursions only on particular nights, and with such regularity that the time of their arrival on the beach can be predicted a year in advance. This phenomenon can be seen on many beaches in Southern California. Shortly after high tide, on certain nights, sections of these beaches are sometimes covered with thousands of grunion depositing their eggs in the sand.

Grunion watching has become a popular sport in Southern California. Since these fish leave the water to deposit their eggs, they may be observed on shore while they are briefly stranded. The common sight of thousands of people lining the more popular beaches in Southern California in anticipation of a grunion run attests to its ever-growing popularity. Often there are more people than fish, so to protect the species, it is important to let them spawn without disturbance. All that is needed to observe grunion is an adventurous spirit and the patience to find a promising beach and then wait for a run to begin." https://wildlife.ca.gov/Fishing/Ocean/Grunion#28425746-introduction