In the life of nearly every Hawaiian green sea turtle hatched at Sea Life Park, a day like yesterday arrives. It's the day they are set free to roam the ocean.

One by one, 16 turtles flippered away from a sandy cove near Makapu'u. Only one in a thousand will reach maturity, the point 20 to 30 years later when they will mate.

But they are part of a larger success story that has seen their population increase by 53 percent in the past 25 years. While not in immediate danger of extinction, Hawaiian green sea turtles, or honu, are a federally protected threatened species.

If the turtle population continues to make progress, the National Marine Fisheries Service and the U.S. Fish and Wildlife Service could decide to remove it from the threatened species list — but only after hearings and scientific reviews.

George Balazs, a biologist with the National Oceanic and Atmospheric Administration, has charted the sea turtles' progress since 1973, when he counted 67 mother turtles breeding at French Frigate Shoals in the Northwestern Hawaiian Islands. Two years ago there were 548.

"It's a wonderful success story," he said. "It's a credit to the people of Hawai'i who have left the turtles alone, obeyed the laws and let the turtles replenish themselves from the horrid depletion of the early 1970s."

Before honu were given federal protection in 1978, turtle meat sold for $1 a pound and Hawai'i fishermen made good money selling them to restaurants, Balazs said.

Most people know they are not supposed to go near, touch or harass a Hawaiian green sea turtle, let alone eat one, Balazs said. Now, even the turtles behave differently.

"The turtles are now familiar with people and do not recognize them as their mortal enemy," he said. "They allow themselves to be seen."

NETS, CIGARETTES KILL

Anyone fortunate enough to see a swimming honu knows how graceful they are, gently gliding through the water with a steady beat of their flippers. They are saltwater reptiles that need to breathe at the ocean's surface every few minutes, but when they are at rest, they can lie on the ocean bottom nearly 2 1/2 hours.

In the wild, the turtles spend almost all their life in the water. But the adult females must return to land to lay their eggs. They will do this several times a year but afterward will wait two or three years before mating again.

Hatchlings are often eaten by fish, crabs and birds, while adults face only one natural predator: tiger sharks.

But every year, turtles drown after becoming entangled in fishing gear or when they are accidentally caught by commercial fishing operations. Turtles, which normally eat only algae, often die after eating discarded pieces of plastic or cigarette butts.

And in Hawai'i, about half of the green sea turtles suffer from fibropapilloma, a disease that causes grapefruit-sized tumors over their eyes, mouth, neck and flippers.

Their quest to reproduce starts each spring. The turtles will swim hundreds of miles to the shoals, where the females can mate two or three times and lay more than 100 eggs each cycle.

"Every turtle that is mature does not go every year because it takes so much energy to migrate and lay their eggs several times," Balazs said. "It takes the mothers a couple years to restore their bodies before they can go back."

HATCHING HONU

The turtles released yesterday from Sea Life Park came from the only breeding colony in the United States. Two were fitted with a 2 oz. electronic device that will allow researchers to track them with satellites.

The younger ones, hatched in the summer of 2005, were 12 to 16 inches long and weighed 9 to 16 pounds. The oldest turtle, hatched in the summer of 2004, was 20 inches long and weighed 49 pounds.

Using a resident population of 18 turtles, the park breeds 200 to 800 turtles a year. A few are kept at the park or loaned to aquariums for educational purposes while the rest are set free, said Jeff Pawlowski, a zoologist who serves as the park's research and education coordinator.

"Those 18 do it," he said. "We have a very small population but they are very productive."

It began by chance. A sea turtle exhibit was built a few years after Sea Life Park opened in 1965 but no one expected the turtles would reproduce.

"In 1976 we started seeing baby hatchlings on the beach and we realized these guys are breeding," Pawlowski said. "And here we are breeding offspring year after year."

Some of those turtles wind up at the Mauna Lani Bay Hotel and Bungalows on the Big Island, where fishpond manager Pii Laeha cares for them. The hotel currently has 21 Hawaiian green sea turtles, he said. Every Fourth of July, the hotel releases its older turtles.

"At Mauna Lani, we call it turtle independence day," Laeha said. "In the last 17 years, we have released over 165 turtles."

FEEL THAT TURTLE LOVE

While at the hotel, the turtles serve as ambassadors for their species.

"We have people come from all over the world," Laeha said. "They come and fall in love with the turtles and go back home and spread the turtle love around."

Some of that love comes from Hawai'i children whose parents still eat turtles — even though it's illegal — because it's part of their culture.

"People have told us they have stopped eating turtles because of their kids," he said. "Every little bit helps."

The turtles at Sea Life Park serve a similar purpose. But when they reach 18 months, they're too big to be cute and it's time to go.

Yesterday, Pawlowski and his staff slipped their turtles into the big blue yonder. Each one was carried to the sea and set free with all the accompanying worry of watchful parents.

"The staff has spent over a year raising them," he said. "They give them names. They weigh them. They feed them. It's like your little baby you're taking down to release into the ocean."

At first the turtles were unsure. After all, they had grown up in a world without currents.

Ocean surges pushed them around.

"There was a little concern," Pawlowksi said. "Some of them were circling back and it seemed they didn't want to leave the bay."

They had to get their bearings, that's all.

"In a few minutes," he said, "these guys were on their way."

Reach Mike Gordon at mgordon@honoluluadvertiser.com.