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What is a Grunion Run!?

California beaches are famous all over the world for their year round sunshine, surfing and maybe even the occasional celebrity sighting. A lesser known, but no less awesome event is the spawning ritual of a small silvery fish called the California Grunion (Leuresthes tenuis). This amazing event is called the ‘Grunion Run’ and it happens at night on a high tide from March through September. 


The California Department of Fish and Wildlife describes their reproductive behavior saying, “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, grunions 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” (wildlife.ca.gov).


The Grunion mating ritual is based on the phases of the moon. During a full moon and new moon, when the tide is at its highest, Grunions swim onto the beaches to spawn and the female Grunion lays eggs above the high tide line. Sea Grant California says, This ensures that the eggs will only be submerged during high tides, which is important because it allows them to get enough oxygen” (caseagrant.ucsd.edu).


The female Grunion uses her tail to dig a small hole in the sand to create a nest and deposit her eggs in the sand. The males curl around the half buried female releasing their semen, called “milt” to fertilize the eggs.  When the fertilization is complete, the female will bury the eggs. Some females can spawn up to 18,000 eggs in a single season (marinesanctuary.org). “Immediately after fertilizing the eggs, the male grunions untwist themselves and wriggle back to the waves. Female grunions eventually squirm free and return to the water as well. A single nest can be fertilized by up to eight male grunions. It can take anywhere from 30 seconds to several minutes for a grunion to come up onto the beach, spawn, and return to the waves” (caseagrant.ucsd.edu).


After the male and female Grunion return to the water, the fertilized eggs remain buried in the sand. The next high tide triggers the baby Grunion to hatch, which takes about ten days. The hatchlings will mature and complete the spawning cycle in about a year (marinesanctuary.org). The Grunion lifespan is three to four years.


The California Grunion is found only along the coast of California. Small and slender, they will only reach lengths of five to six inches on average. The Grunion belongs to the Atherinidae family and are given the nickname “silversides”. They are distinguished as members of this family by the, “shiny, silvery stripes found along [their] blue-green backs” (marinesanctuary.org). The Grunion are most abundant around the Channel Islands National Marine Sanctuary and remain close to the surface in shallow waters (marinesanctuary.org). The California Grunion habitat ranges from Point Conception, California to Punta Abreojos, Baja California. “About 90% of the population is thought to live off the Southern California coast in San Diego, Los Angeles, and Orange Counties'' (caseagrant.ucsd.edu).


The National Marine Sanctuary Foundation gives an interesting history on the origin of how the grunion got its name, “These fish were named grunion, or ‘grunter,’ by early Spanish settlers, presumably because of the subtle squeaking sounds emitted by these fish during mating” (marinesanctuary.org).


According to the California Sea Grant, the Grunion population has been declining over the last decade for a variety of reasons. They are being hunted illegally without permits and taken with nets and other types of gear. During the open season, Grunions may only be taken by hand and there is no hole digging allowed. “The daily bag and possession limit is 30 grunion per person. Recreational fishing license holders and persons under the age of 16 may handle grunion gently during the open season, and release them back into the water unharmed. Grunion may not be pursued or handled at all during the closed season (April - June)” (wildlife.ca.gov).


Grunion eggs that are still in the sand are also in danger from combing or grooming the beaches because the eggs can be dislodged and washed out to sea before they are mature enough to hatch (caseagrant.ucsd.edu). 


Another factor affecting the Grunion population is climate change. According to the National Park Service, “Grunions expanded their range to the San Francisco Bay — and to their northernmost habitat in Tomales Bay — as a direct result of climate change. The warming oceans and shores will continue to push them north” (www.nps.gov.).



Want to see a Grunion Run?


The California Department of Fish and Wildlife publishes a schedule that predicts the grunion run at Cabrillo Beach near the Los Angeles Harbor entrance (wildlife.ca.gov). Cabrillo Aquarium also hosts grunion runs where you are able to participate in the hatching of captive grunion eggs.


The California Sea Grant has these guidelines for watching a grunion run:

  • Do your research, check websites like the California Department of Fish and Wildife's Grunion Facts & Expected Runs page or grunion.org to check the best locations and times to view. 

  • Check local beach regulations before heading out. 

  • Be prepared. It can be cold and damp on the beach at night even in the summer months, so bring appropriate clothing and footwear.  

  • Look for darker, calm portions of beach where the grunion may prefer to spawn. Also, be aware of your surroundings, your safety is your biggest priority, do not go to dark areas if they do not seem safe. 

  • Keep your voice low while waiting for grunion. 

  • Use a red light to navigate the beach at night. The red light will not disturb the fish. 

  • If you need to move locations, walk higher up on the beach away from the wet sand. 

  • Leave your pets at home.

  • Once the grunion start their run, you can approach them more closely and respectfully. Do not touch the fish or interfere with their spawning. 

  • Be careful not to step on any grunions!


“Grunions are sensitive to light and vibrations on the beach. If there are bright lights that are moving, or they can feel vibrations from people walking on the sand, they may not come up onto the beach to spawn” (caseagrant.ucsd.edu).


In order to help preserve and protect our wildlife and their environment, it’s always important to respect their natural habitat and observe them from a safe distance. For additional information about the California Grunion check out these websites:

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