Biscayne National Park. Some of the green turtles removed from a nest last month at Biscayne National Park. It was the first green turtle nest ever documented there. The turtles were released in the ocean.

When the late Archie Carr, a pioneering University of Florida ecologist, first began documenting the decline of sea turtles in the 1960s, the future looked grim — particularly for the green turtle.The green turtle had long been a Florida seafood menu staple, usually served up in the famous soup. But with the population largely eaten out of existence in state waters, most meat had to be imported. To make matters worse, eggs were routinely poached from beach nests. And hatchlings, attracted the lights of growing coastal communities, crawled inland rather than out to sea, dying in the hot sun or under car tires.At the low point, Carr estimated there were no more than 30 to 40 green turtle nests along the entire Florida coast, its primary nursery ground.

Now, greens are in the midst of an unprecedented nesting boom from South Florida to South Carolina.

With a month left in nesting season, Florida wildlife managers say preliminary numbers show green turtle nesting has more than doubled statewide. Biologists have already tallied a record 11,500 nests in one 20-mile stretch alone — in the national refuge south of Melbourne Beach that bears Carr’s name — doubling a high set only two years ago.

Green turtles, which average 350 pounds when full-grown, have even crawled ashore in not-so-inviting areas like rocky oceanside Elliott Key, giving Biscayne National Park its first documented green turtle nest.

“It’s just a miracle,” said Llewellyn Ehrhart, a University of Central Florida zoologist who has monitored nesting in the Archie Carr National Wildlife Refuge for decades. “This is one of the greatest positive stories in the history of wildlife conservation in America, mostly because they were decimated so badly.”

Ehrhart and state and federal wildlife managers credit a host of save-the-sea-turtle measures enacted over the past few decades for the resurgence of nesting in the southeastern United States. Two other species that most commonly nest in Florida, the loggerhead and leatherback, also have been on a general upward trend, but not one nearly as dramatic as the green turtle.

“It’s very positive, and 20-plus years of conservation efforts are really starting to pay off,” said Ann Marie Lauritsen, acting national sea turtle coordinator for the U.S. Fish and Wildlife Service.

Those efforts include seasonal lighting ordinances adopted by an increasing number of coastal communities to reduce street and building lights that confuse nesting turtles and development restrictions that have preserved crucial nesting sites like the Carr refuge, which Congress created in 1991. Its beach, which straddles Brevard and Indian River counties, typically produces about half the state’s turtle nests.

A ban on gillnets that Florida enacted in 1994 to protect dwindling stocks of redfish, mullet and other shallow-water species probably had a healthy ripple effect on green turtles, which are vegetarians often found foraging in the same sea-grass meadows. Turtle extruder devices fitted to shrimp trawlers that allow turtles to escape nets and death as “by-catch” may have helped as well — but more for deep-water species such as the loggerhead and leatherback.

Ehrhart and Blair Witherington, a scientist for the Florida Fish and Wildlife Conservation Commission, believe the rebound really began in 1978, when the green turtle was added to the federal list of endangered species. The declaration banned the harvest of eggs, turtle fishing and any sale of sea turtle meat, domestic or imported. All five of the species that nest in Florida remain on the list today, with the green, leatherback, hawksbill and — rarest of all — Kemp’s Ridley all considered at the highest risk. The loggerhead, the most common turtle, is listed as threatened.

“When we stopped eating them, that was a pretty big effect,” said Witherington. “Lo and behold, you stop hitting them on the head and killing them, and they come back.”

Still, it took quite a while for sea turtles, which can live 60 or more years and do not typically reach breeding maturity for 20 to 30 years, to respond.

When Ehrhart started his beach surveys in 1982, he found fewer than 50 nests in the Archie Carr. By the early 1990s, the numbers began to bump into the hundreds. Over the past decade, it bounced in and out of the thousands, hitting 5,500 in 2011. This year, he was shocked and thrilled to see nesting numbers leap above 10,000. Overall, he said, it represents a growth rate that, he believes, may be unprecedented in wildlife-conservation efforts.

Nesting is up across the green turtle’s range, said Lauritsen, with increases in South Carolina, North Carolina and Georgia as well. South Florida, which doesn’t get nearly as many nests as Central Florida, has still seen its numbers jump.

“Overall in the last 33 years, I think 11 is the most we’ve had,” said Bill Ahern, Miami-Dade County’s longtime sea turtle conservationist. “We’re looking at 32 green nests so far [this year]. It’s been amazing.”

In Broward, green turtle numbers rose from 209 last year to 458 so far this year, said Courtney Kiel, a natural resources specialist with Broward County.

One determined turtle even managed to nest on Elliott Key in Biscayne Bay, lumbering over jagged rock, then digging out plants and sand on a narrow dune strip — the first green nest ever documented in Biscayne National Park. Only about a third of the hatchlings were able to escape the thick brush on their own, so park biologists plucked out 66 others and released them in the ocean last month.

Add the 18 nests that loggerheads dug in the park, and you have an explosion of activity, said park biologist Vanessa McDonough. “Nineteen nests may not sound like a big number to a lot, but in the last eight to nine years we’ve averaged four,” she said.

Despite the encouraging increases, wildlife manages are not ready to pronounce sea turtles out of danger. Populations of some species remain precariously low. Kemp’s Ridley turtles, which mainly nest on the Mexican Gulf Coast but sporadically are found in Florida, are thought to number fewer than a thousand nesting females. The hawksbill is also rare. Nests of the massive leatherback can sometimes number in the dozens in Florida.

Nesting also runs in cycles, with turtles traveling hundreds or thousands of miles to return to build nests in the same areas where they were hatched. The output can yo-yo from year to year for reasons that are not always clear. Loggerheads, the most common turtle, began to decline starting in the late 1990s, but nesting has more recently gone up and down.

“At this point, it’s tough to tell for loggerheads what the long-term trend will be,” said Lauritsen.

Green turtles still face a host of threats, many shared by other species. Because they frequent coastal waters, boat strikes kill or injure many turtles. They are also exposed to toxic algae blooms like red tide, as well as potentially fatal freezes. Pollution and development can degrade and damage their habitats.

And while many countries have also begun to ban the harvest of eggs and meat, turtles still wind up legally and illegally in plates and bowls in some countries. There is also the question of climate change and whether rising sea levels will swamp beaches and nesting areas.

Two years ago, the U.S. Fish & Wildlife Service and the National Marine Fisheries Service conducted a global reassessment of loggerheads, dividing them into nine separate populations and leaving the American populations listed as threatened. The agencies are now conducting a similar analysis for green turtles, but Lauritsen said it was too soon to speculate whether the nesting boom would be enough to removed its endangered tag.

Still, there is a lot more hope than there was a few decades ago.

Miami-Dade’s Ahern, who grew up in South Florida, recalls being appalled as a teenager in Miami Beach when he crossed Collins Avenue and found the road “carpeted with dead sea turtle hatchlings.”

There has been a sea change in public support for recovery efforts and turtle-friendly ordinances. In many coastal counties, crews survey beaches every morning to mark nests, but poaching reports remains rare.

Under state rules, biologists also now save nests that once might have been destroyed — in construction sites, for example, or below the high-tide line, where waves might wash away sand and expose the eggs.

“After all these years, it really feels like we’re making headway,” Ahern said.