In the wild, the life of green sea turtles is an extraordinary odyssey in which primeval instinct guides them across hundreds of miles of open ocean to retrace a trip they have not made in 25 years–a return to the exact patch of beach where they were born.
The turtles, which range far and wide in the ocean immediately after hatching, stay away from their home beach until they reach sexual maturity 25 years later. How they find their way back to spawn their own young after so many years has left scientists flummoxed and fascinated for decades.
In a contemporary twist driven by the creature’s near extinction in some parts of the world, scientists are now testing the idea of placing captive-bred, hand-reared turtles from zoos and aquariums back into the wild. If it works, captive-born turtles may replenish wild populations that are in danger of disappearing.
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The big question, though, is where the captive-bred turtles will go to lay their eggs, since they can’t return to their human-engineered birthplaces.
Two 3-year-old turtles at Brookfield Zoo, known to their keepers as Magnum and Higgins, are about to join the experiment. They are scheduled to be flown to Hawaii in the next week or two, where they will be released into the wild July 4 from a beach on Oahu.
Born on an artificial beach inside an aquarium, there is no possibility that Magnum and Higgins–no matter what instinct may dictate–can swim back there.
How they will deal with that is a scientific soap opera that will twist and turn for the next 22 years, when Magnum and Higgins reach sexual maturity. Will they simply follow wild-born turtles back to traditional mating beaches? Will they take off in some unforeseeable direction? Will they simply do nothing, or go mad? Stayed tuned in the year 2021. . .
“This is an experiment,” said George Balazs, head of the National Marine Fisheries Service marine turtle research office in Oahu, in a telephone interview about the July 4 releases. “There are great big question marks about how well (captive-bred) turtles can adapt to the wild, and whether they can grow and become breeders.”
Balazs has been monitoring the progress of captive-bred green sea turtles into Hawaiian waters since the program began in 1990. All the turtles were bred and hatched at Oahu’s Sea Life Park Aquarium but sent to various zoos and aquariums around the U.S. for hand-rearing until they are old enough for wild release.
Magnum and Higgins came to Brookfield from Sea Life Park three years ago, progressing here from little tykes to 80-pound adolescents.
Now old enough and big enough for the wild release, they were given physical exams last week at the zoo’s hospital pending their trip back to Oahu.
They will join about a dozen other juvenile, hand-raised green turtles at a “halfway house,” all returning from the institutions to which Sea Life Park farmed them out three years ago.
Some halfway house. It is a group of large, manmade turtle lagoons at Oahu’s Mauna Lani Resort. There the young turtles will learn how to forage for food and live on their own in preparation for their release into the wild.
Once they get the hang of taking care of themselves, on July 4 they will be the center of a great deal of attention. Local celebrities, politicians and resort guests will remove the turtles from the lagoons, take them to the beach and release them in the ocean, celebrating “Turtle Independence Day.”
Green sea turtles have been disappearing in some places because human settlements were built on beaches where turtles once nested, and in others because turtles have been hunted for their meat and shells.
Green sea turtles in Hawaii earlier this century were hunted nearly to extinction to supply the tables of tourist restaurants with turtle steaks. In fact, green turtles, which are brown, get their name from their succulent meat, which is green-tinted.
Since 1978, sea turtles in U.S. water have enjoyed federal protection. The population of adult Hawaiian green sea turtles, which weigh 450 pounds and are 3 1/2-feet long, has been growing nicely.
Even in the most pristine conditions, for a green sea turtle to survive into adulthood, it must overcome incredible odds: Only 1 in 1,000 makes it.
The wild turtles that Magnum and Higgins will join July 4 along the coast of Oahu were hatched in the wild about 500 miles west of Oahu, on a beach on French Frigate Shoals, a stretch of ragged, uninhabited atolls.
Every year on the atolls, thousands of green turtle hatchlings emerge from golf-ball-sized eggs, laid in batches of 50 to 150 in pits dug in the sand by their mothers. They immediately sprint for the ocean, but a large percentage are caught and eaten by crabs and birds before they reach the water.
Once in the water, thousands become lunch for fish. Those that survive swim into currents that carry them far offshore, where they bob on the surface over water thousands of feet deep, Balazs said. If not eaten by some other creature, they remain far from land for at least two years, growing rapidly on a diet of tiny squid and plankton.
When they reach a weight of a few pounds, they are too big for most of their natural predators, and they swim back to shore. Except to travel to mating beaches, they remain in shallow coastal water for the rest of their long lives, foraging on seaweed and grasses.
At 80 pounds, Magnum and Higgins are so big they will not be bothered by most predators when they are released in the wild, wearing identifying microchips under their hides.
For the past eight years, through an ongoing capture-and-release program of both wild and captive-bred turtles, Balazs and his staff have followed the progress of several dozen hand-reared animals set free since 1990.
“We’ve seen some encouraging signs,” Balazs said. “A number of them have shown nice signs of growth since their release, though others have shown they haven’t got their act together and haven’t progressed so well.”
When the first of the captive-bred turtles reaches sexual maturity, in the year 2015 or so, the presumption and hope is, Balazs said, that they will follow wild turtles to French Frigate Shoals, thus rejoining the natural life cycle.
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Magnum and Higgins were the first turtles Brookfield took from the program, bringing them here to be a part of its Living Coast exhibit that opened two years ago.
“We feed them by hand,” said Lee Jackson, the Living Coast’s collection manager, of Magnum and Higgins, “because we have to be sure that each gets the proper amount of food.
“They very definitely react to us when we show up, because they know we represent food. Magnum is a little more aggressive and is right there for feeding, but Higgins is a little more timid and hangs back a bit.”
Once Magnum and Higgins are gone, Jackson said, Brookfield will get two more turtle tykes from the Hawaiian aquarium.
“They have two animals already selected for us,” he said. “Their health certificates are being prepared, and then they’ll be shipped to us. We’ll have them on display after they spend about a month in quarantine.”