Four college students marched in darkness through the damp sand of Laguna Beach, clutching plastic buckets and garden trowels to stalk an enigmatic fish.
So began a night of messy detective work to crack mysteries that have long bedeviled scientists enchanted with grunion, a creature tied to Southern California's surf's-up culture.
The peculiar 6-inch-long fish, which spawns on sandy beaches, puts on a curtain-call performance each year, scurrying from high tide to partake in a mating ritual with all the haste of a teenager out past curfew.
Beyond its amorous habits, the silvery creature beguiles biologists, who can't say for certain where it swims, what it eats or whether the state of its health can indicate hazards in the oceans and on beaches.
The lengthy list of unknowns is partly due to the grunion's flightiness and its distaste for captivity, which make it difficult to observe.
But "when you see the little fish climbing out of the water, it's like they're begging to be studied," said Nina Karnovsky, an assistant professor of biology at Pomona College.
So four budding researchers -- Karnovsky's undergraduate students -- are spending the summer sleuthing on Laguna Beach, using creative methods to understand the fish, including hauling grunion eggs to a lab and packing them into kiddie pools with sand, which one student walks on to see whether that harms the eggs.
Unlocking the grunion's secrets also appears to require dodging homeless men, kissing couples and "fish-kickers," who, as the students observed last week, shriek at the sight of fish quaking in the sand and try to bat them away.
"There are these fish and they come up onto the beach and mate" is how Max Kowal, 20, explains his research to friends, "and I gather their eggs and step on them."
The grunion legend is as much a part of Southern California beach lore as sand pails and bodyboards, with several musical odes to them, most titled "Grunion Run." The state Department of Fish and Game website lists cooking tips: Roll in flour and yellow corn meal, deep-fry, sprinkle with salt.
It wasn't until the 1940s that the fish sparked scientific interest, when Boyd W. Walker, a marine biologist at Scripps Institution of Oceanography in La Jolla, realized that the fish's mating cycle was tied to the tides.
Six decades later, environmentalists have pointed to the grunion in debates about whether grooming sand may harm the beach ecosystem.
State officials mentioned them in a lawsuit filed last year against Malibu homeowners who hired bulldozers to scoop sand from a public shore, saying their action disrupted grunion spawning.
Meanwhile, researchers are exploring whether grunion -- named for the Spanish word for "grunter" -- drop clues to the beaches' ecological health, since they make regular appearances on the sand and in water.
This much is certain: After the highest tides triggered by a new or full moon, usually from March through August, the fish shimmy from waves mainly on Southland and northern Baja California beaches. Some have been seen as far north as San Francisco Bay. The females bury eggs under slick sand, which cradles them for about two weeks, until the high tide shakes them open and washes the young grunion home.
"Think about it," said Caitlin Guthrie, 20, one of the Pomona College researchers. "There's a whole other world under the sand that we know so little about."
Under a round, yellow moon, Guthrie and the other students huddled last week near a Laguna Beach lifeguard stand to better understand the grunion's mysterious rites.
The students carved the beach into five zones, each about 140 paces long, to monitor how the 8,000 to 20,000 people who stroll it each day affect the nocturnal fish.
While sunbathers baked, Guthrie counted toddlers, gulls and more, whose numbers were compared with what the students collected at night: grunion and grunion eggs.
The researchers' first grunion squirmed from the ocean at 10:56 p.m., Casey Williams, 20, jotted in a notebook. The students spread along the shore, murmuring updates into earpieces connected to walkie-talkies: "Fish in Zone 2. Fish in Zone 2."
The grunion ritual unfolded:
The female dashed onto the beach and drilled herself into the shore, with her head flailing above the sand as she discharged as many as 3,000 eggs. Several males appeared to envelop her head and emitted milt, which fertilized the eggs.
The spawning took seconds. Then the males hustled back to the ocean while the female pulled herself out of the sand and followed them.
It was a routine that hundreds, sometimes thousands, of grunion performed over an hour or more, as Sonia Fang, another researcher, dashed along the shore, plucking as many as 10 with her bare hands and slipping them into plastic bags.
"They're hardy little things," she said. "I try to grab them but they just hop on out."