The Phenomenon of California Grunion Runs

Along the Southern California coastline, a remarkable natural event captivates both locals and visitors alike — the grunion run. This nocturnal spectacle, where thousands of small, silvery fish emerge from the ocean to spawn on sandy beaches, offers a unique opportunity for observation and participation. Understanding the intricacies of this phenomenon enhances the experience and fosters appreciation for this distinctive marine behavior.

What Is a Grunion?

The California grunion (Leuresthes tenuis) is a species of marine fish endemic to the coastal waters of Southern California and northern Baja California. These slender, silver fish typically measure between 5 to 6 inches in length. Unlike most fish, grunion exhibit a unique reproductive behavior by coming ashore to spawn, making them a subject of fascination and study. ​

Understanding the Grunion Run

A grunion run refers to the spawning events during which these fish leave the ocean en masse to lay their eggs on sandy beaches. Triggered by high tides associated with full and new moons, these runs occur predominantly between March and August, with peak activity from late March to early June. During a run, female grunion burrow into the sand to deposit eggs, while males wrap around them to fertilize externally. The eggs remain buried until the next series of high tides, approximately 10 to 15 days later, when they hatch, and the larvae are carried out to sea. ​

Participating in a Grunion Run

For those interested in witnessing or engaging in a grunion run, here are key considerations:​

• Timing: Grunion runs are predictable events. The California Department of Fish and Wildlife (CDFW) provides annual schedules indicating expected run times. For instance, in 2025, runs are anticipated on various dates from March through August. ​
• Licensing: Individuals aged 16 and older must possess a valid California sport fishing license to catch grunion. Licenses are not required for observation alone.
• Methods: Grunion may only be caught by hand; the use of nets or other gear is prohibited. Digging holes to trap grunion is also not allowed. ​
• Regulations: There is a daily bag and possession limit of 30 grunion per person. However, during the closed season — from April through June — grunion may not be taken, allowing them to spawn undisturbed.

Best Practices for Observers and Participants

• Preparation: Arrive at the beach 30 to 60 minutes after high tide, as runs typically begin within this window and can last from one to three hours. ​
• Respect: During the closed season, observe without disturbing the fish. Even during the open season, consider practicing catch and release to support conservation efforts.​
• Environment: Use flashlights sparingly to avoid disorienting the fish, and refrain from loud noises or sudden movements that could disrupt the spawning process.​

Conservation and Cultural Significance

Grunion play a vital role in the coastal ecosystem, serving as prey for larger fish, birds, and marine mammals. Their eggs also provide nourishment for shorebirds and invertebrates. Historically, Indigenous communities harvested grunion during spawning runs, a practice that continues to hold cultural significance today.

The grunion run is a testament to the wonders of marine life along California’s shores. Whether participating hands-on or simply observing, this phenomenon offers a memorable experience that underscores the importance of preserving our natural heritage. By adhering to regulations and practicing responsible stewardship, we ensure that future generations can continue to marvel at this extraordinary event.​

For more information and detailed schedules, visit the California Department of Fish and Wildlife’s grunion page at wildlife.ca.gov/Fishing/Ocean/Grunion.