California Grunion, Leuresthes tenuis
California Grunion, Leuresthes tenuis. Photographs of live fish making their reproductive run on the beach late evening, Solana Beach, California, March 2019. Photographs and identification courtesy of Ben Cantrell, San Diego, California.
California Grunion, Leuresthes tenuis. Fish caught from within Mission Bay, San Diego, California, August 2018. Catch, photograph and identification courtesy of Luke Ovgard, Klamath Falls, Oregon.
The California Grunion, Leuresthes tenuis, is a member of the New World Silverside or Atherinopsidae Family, and is known in Mexico as pejerrey californiano. Globally, there are two species in the genus Leuresthes, both found in Mexican waters of the Pacific Ocean.
The California Grunion has a long slender bodies with a deeply forked tail. They are greenish dorsally and silvery ventrally. They have a blue patch on their checks and a silvery-blue lateral line on their sides. Their anal fin originates below their first dorsal fin and has 1 spine and 21 to 24 rays; their first dorsal fin has 5 to 7 rays; their second dorsal fin has 1 spine and 9 to 10 rays. They have 33 to 36 gill rakers.
The California Grunion is a non-migratory coastal fish found inshore in large schools at depths up to 18 meters (60 feet). They reach a maximum of 19.0 cm (7.5 inches) in length. They consume plankton. In turn they are preyed upon by the California Halibut, Rock Bass, White Croaker, and other large predators including sea lions. Their eggs are consumed by shore birds including the Marbled Godwit and Whimbrel, and by beetles, flies, isopods, sandworms and ground squirrels. The California Grunion is a major scientific curiosity as they have a unique breeding strategy. Reproduction is oviparous with breeding occurring between April and August on the highest tides of the second, third, and fourth nights following either a new moon or a full moon. Fish surf the large waves well up onto the beach just above the high tide line and each female digs herself tail first into the sand and lays a clutch of 1,000 to 3,600 eggs in the wet sand, which are fertilized by one or more males who then quickly retreat to the sea. The complete process requires less than two minutes. The eggs are bright orange but gradually change to sand color; they hatch in about 15 days following the next new moon or large tidal episode. Juveniles rapidly develop reaching sexual maturity within 1 year. This reproduction cycle is repeated 4 to 8 times a year. The oceanic lifestyle of the California Grunion is not well understood. They are short-lived and have lifespans of four years.
The California Grunion is a resident of Mexican waters of the Pacific Ocean but has a limited distribution being found from Magdalena Bay, Baja California Sur, northward along the central and northwest coasts of Baja.
The California Grunion is similar to, and can be easily confused with, the Gulf Grunion, Leuresthes sardina (found only in the northern portions of the Sea of Cortez). It is also very similar to the Jacksmelt, Atherinopsis californiensis (first dorsal fin inserted before anal fin) and the Topsmelt, Atherinops affinis (first dorsal fin behind origin of anal fin).
From a conservation perspective the California Grunion has not been formally evaluated. Commercially they are caught with encircling nets and used on a limited basis for human consumption or as bait. Catch levels by both commercial and recreational fishermen have not been monitored, thus their population status is unknown. They are caught by recreational fishermen off the beach by hand, without nets or other tools, during spawning runs. A fishing license is required but no daily catch limits have been established. They are actually tourist attractions with many seeking a view of their unusual mating behavior along the beaches of southern California. They are however, not abundant, elusive, and unpredictable, thus there are often more humans than grunions on the beach and when fish show up, the majority are captured. They are strongly affected by poaching during closed seasons, the illegal use of nets during open seasons, and difficulties in enforcement because all activities occur under the cover of darkness. Beach erosion, beach grooming, sand replenishment, coastal construction, foot traffic, artificial lights, and pollution all have a major negative impact on the spawning of the California Grunion.