In a natural display of exhibitionism, thousands of fish will flop up onto Santa Barbara beaches this summer to do the nasty while researchers watch intently.

California grunion (Leuresthes tenuis) are sardine-sized fish found only off of the coast of Southern California and Baja California, Mexico, that swim to shore — and then up onto the sand — during the spring and summer to participate in a unique mating ritual. Once on the beach, they will be met and observed by members of Grunion Greeters, a research program working to determine exactly how the grunion decide when and where they will breed during a given season.

Dr. Karen Martin, project director of Grunion Greeters at Pepperdine University, said grunion spawn completely out of water on the beaches of Southern California shortly after high tide. They leave the water at night and ride the waves up to shore. The female grunion twists and turns until she is buried halfway in the sand. There, she deposits her eggs and waits for the male grunion. A male wraps his body around the female’s and releases milt, which contains the sperm that will fertilize the eggs, and then immediately retreats back into the ocean.

Up to eight males will fertilize a single female grunion. The female grunion will then wiggle free from the sand and return to the sea. The fertilized eggs remain in the sand for 10-15 days until the tide sweeps them into the ocean, where they will eventually hatch.

“The grunion runs, as they’re called by scientists, occur on a semi-predictable schedule each month during the spring and summer that coincides with the lunar schedule,” Martin said.

Martin said grunion runs usually occur between 10 p.m. and 4 a.m. the night before a full or new moon. She said Grunion Greeters was created to track the size of grunion populations — whose unusual breeding habits make them especially vulnerable to threats on the shore — up and down the California coast.

“Grunion Greeters was a project initiated in San Diego as a response to the threat of grunion extinction as caused by beach grooming in 2002,” Martin said. “Any disturbance of the beach sand, such as the common practice of raking it with a tractor, can be detrimental to the grunion eggs.”

Last year, the program was expanded to track spawning grunion at more South Coast locations, including three in Santa Barbara County, Martin said. Monitoring currently takes place at Stearns Wharf and Leadbetter Beach in Santa Barbara, as well as Goleta Beach.

This year, Grunion Greeters is also watching beaches along the coast up to the Bay Area in an effort to determine how far north the grunion’s range extends.

Martin said expanding the program provides researchers with a clearer picture of when and where grunion will spawn, and helps scientists learn more about coastal ecology.

“The grunion can teach us a lot because they are so closely tied to the shoreline ecosystem,” Martin said. “We use grunion to understand beach ecology to further understand the relationship between fish, their predators and their habitat.”

The Grunion Greeters program in Santa Barbara is coordinated by Leigh Ann Grabowsky, director of Watershed Programs for Santa Barbara Channelkeeper.

“Volunteers offer their time to monitor grunion runs, which usually occur late at night and only on certain nights,” Grabowsky said.

Often, observers will watch for grunion and not see any at all, but Grabowsky said she is hopeful that this will be a productive breeding season for the fish.

“This year, we have had good luck,” Grabowsky said. “During good runs, we have seen many fish.”

The observations are recorded, compiled and sent to Pepperdine University, where Martin and other researchers process the data and look for trends in the timing and location of the grunion runs, Grabowsky said.

“There are no noticeable trends for the Santa Barbara beaches,” Grabowsky said. “But all the data has not been processed.”

She said a report of the observations will be published later this year and presented at scientific conferences.

Many UCSB faculty, staff and students have participated in the Grunion Greeters program, as well as grunion enthusiasts hoping to catch a glimpse of the fishes’ elaborate mating ritual, Grabowsky said.

“The first time I saw a grunion run was an evening I was out walking on the beach,” said Amy Musante, a graduate student in Ecology, Evolutionary and Marine Biology. “I just happened upon them and I had no idea what was going on.”

Musante said a few Grunion Greeters who were monitoring the fish at the time explained the Grunion Greeters program to her and how the grunion spawn. She said she immediately became interested in the program and now volunteers to count the grunion.

On her three shifts this spring, she said she has counted over 1,000 fish at Goleta Beach. She said she enjoys greeting the grunion and encourages others to witness the spectacle.

“On one night, I went to Goleta Beach and hundreds of grunion were already spawning,” Musante said. “Later that evening, a small shark came up onto the beach and began foraging on fish. Other times, birds or seals attend the grunion run for a midnight feast.”