The California grunion is one of two species of silversides in the genus Leuresthes that are known for their unusual mating behaviors (see below). This species lives off of the coast of California and Baja California, and the closely related Gulf grunion (Leuresthes sardinas) is restricted to the northern Gulf of California, Mexico.
California grunion are plankton eaters; they eat small, pelagic crustaceans and other zooplankton. Though they eat very small prey, they use their relatively large eyes and strong eyesight to attack individual prey. This strategy is in stark contrast to that used by the very large bodied filter feeders (like whale sharks and basking sharks), which essentially feed blindly and rely on large volumes of water to obtain sufficient prey. California grunion are an important prey species in coastal ecosystems, particularly when they come to shore to reproduce.
The grunions’ unique reproductive behaviors contribute to them being well-known species throughout their ranges. During the spring and summer, the California grunion forms very dense aggregations of both males and females that come very close to shore during the highest tides surrounding new and full moons. When the tide is at its peak high, these fish ride waves onto the beach, where females dig small holes and deposit their eggs. Males fight each other to fertilize the eggs, and the females bury them. California grunion reproduce at night, while Gulf Grunion conduct the same behaviors but during the day. When mating, these fishes are eaten by seabirds, crabs, and other species, and they are sometimes collected for human consumption. Individuals often become stranded by the receding tide. After an incubation period of at least ten days (usually longer), the eggs hatch, when stimulated by the return of the next month’s highest tide.
The conservation status of the California grunion is unknown, but some spawning locations have been negatively affected by beach development or overharvesting. It is important that managers continue to monitor California grunion populations to ensure that these human activities do not seriously threaten this interesting species.
Oceana joined forces with Sailors for the Sea, an ocean conservation organization dedicated to educating and engaging the world’s boating community. Sailors for the Sea developed the KELP (Kids Environmental Lesson Plans) program to create the next generation of ocean stewards. Click here or below to download hands-on marine science activities for kids.