California Grunion, Leuresthes tenuis
The California Grunion, Leuresthes tenuis, whose common Spanish name is pejerrey californiano, is a species in the New World Silverside or Atherinopsidae Family, known collectively as charales and pejerreyes in Mexico. Globally, there are only two species in the genus Leuresthes, both found in Mexican waters of the Pacific.
The California Grunions have 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 one spine and 21 to 24 rays. They have two dorsal fins, the first with 4 to 8 spines and the second with 8 to 10 rays.
The California Grunions are non-migratory coastal fish found inshore in large schools at depths up to 18 meters (60 feet). They reach a maximum length of 19.0 cm (7.5 inches). They consume plankton. 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 sandworms, ground squirrels, isopods, beetles, and flies.
The California Grunions are 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 fifteen days following the next new moon or large tidal episode. Juveniles rapidly develop reaching sexual maturity within one year. This reproduction cycle is repeated four to eight times a year. The oceanic lifestyle of the California Grunion is not well understood. They are short-lived and have a maximum lifespan of four years.
In Mexican waters the California Grunions have a limited distribution being found only from Magdalena Bay 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).
The California Grunions 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 at night. Beach erosions, 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. 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 have not yet been evaluated from a conservation perspective.
California Grunion, Leuresthes tenuis. Fish caught from coastal waters off Carlsbad, California, July 2016. Length: 8.4 cm (3.3 inches). Catch, photo, and identification courtesy of Ben Cantrell, Peoria, IL.