FOR almost a year the only world each of them knew was a three-gallon yellow plastic bucket in a Galveston greenhouse. But on a warm spring day last month, 1,631 Kemp's ridley sea turtles were plunked into the Gulf of Mexico to begin the biggest swim of their lives - a swim for survival against the encroachment of man upon their environment. The turtles were part of a nine-year-old Headstart program designed by the National Marine Fisheries Service (NMFS). The aim of the program is to bolster the Gulf's dwindling Kemp's ridley population and to reintroduce the species' egg-laying females to beaches on Texas' South Padre Island. The 10-month-old hatchlings, now averaging two pounds, had been trucked for four hours from Galveston, Texas, to the University of Texas marine sciences laboratory at Port Aransas, where - six to eight to a cardboard box - they were stacked up, dormitory style, on the university's marine research vessel.
Two hours later and 14 miles out to sea, the turtles were dropped into the Gulf by workers - from NMFS, Texas A&M University, the Houston Zoo, and a turtle conservation group - with the proper permits for handling a species listed since 1978 in the Endangered Species Act.
``We're not too sure where they're going,'' said Tim Fontaine, watching the tiny turtle splashes behind the boat spread out and then disappear. ``But we do know they do pretty well,'' added Dr. Fontaine, a fishery biologist and Headstart manager, ``because we've later done autopsies on our turtles that had grown quite a bit and had bellies full of crab and shrimp and other good things.''
The Headstart program began as part of a joint United States-Mexican effort to save the Kemp's ridleys, the most threatened of five turtle species that roam the Gulf. In 1947 a Mexican farmer had taken pictures of an amazing sight: more than 40,000 Kemp's ridley females nesting on one beach south of Rancho Nuevo. By 1978, only about 600 females were returning to the beach, the only place where the species is known to nest.
Today Mexico protects the beach at gunpoint (from poachers who would steal turtle eggs for food or for what some believe is their aphrodisiac quality), and each year the US receives 2,000 turtle eggs for the program.
One popular theory is that the Kemp's ridleys return to the Mexican beach because they are ``programmed'' to return to the sands in which they were born. Following that theory, the US turtle eggs are incubated in South Padre Island sand. When first hatched, the turtles are allowed to crawl across the beach that researchers would like them to choose as a nesting place. One female did lay her eggs on South Padre Island in 1984, but it is not known whether she was a Headstart turtle. It is generally assumed that the females begin laying eggs after about 10 years, an age even the oldest Headstart turtles have not yet reached.
Once the hatching process, called ``imprinting,'' is complete, the hatchlings are scooped up and taken to the NMFS ``turtle house'' in Galveston for nine months of growing in a bucket. (The first ``class'' of turtles in 1978 was allowed to swim together in tanks, but the turtles' aggressive nature resulted in many bitten feet and flippers.)
The turtle house, formerly the site of shrimp experiments, looks like a greenhouse, and inside it sounds like a fairly busy swimming pool. Only here, the noise is caused by thousands of four-inch turtle flippers that never quit moving. ``They have a lot of personality if you're around them a lot,'' said Kathy Indelicato, a biologist who has worked with the turtles for three years. ``There are the ones that bite, those that don't, and then the ones that splash you anytime you walk by.''
While tagging and weighing the turtles in preparation for their release, Ms. Indelicato reflected on the controversy between Gulf shrimpers and turtle conservationists. The focus is on escape hatches, called turtle excluder devices, that environmentalists believe could save more than 10,000 turtles a year from drowning in shrimp nets. Shrimpers say the devices threaten their catch, and would save few turtles. ``I guess I can understand'' the shrimpers' point of view, said the biologist, ``but especially for the Kemp's ridleys it's gotten to the point where we all have to do our part to save them.''
Several days later, Indelicato showed only a faint smile as the last of this year's hatchlings slipped, kicking and flipping, into the Gulf.
``I know a lot of them will die,'' she said, ``but to me it's important, even if we don't often see them, to try to keep them going.''
Still, she added, ``I don't think any of us will really celebrate until that first tagged female nests on Padre Island.''