I am a biologist who, for 29 years, has studied marine turtle nests on the beach at the Archie Carr National Wildlife Refuge, a 21-kilometer stretch of beach on Florida's east coast between Melbourne and Vero Beach, home to nests for three species of turtle.
For loggerheads, it is arguably the best nesting beach on the entire rim of the Atlantic Ocean. For green turtles, it is certainly the best nesting beach in the United States. And for leatherbacks, it is home to a small but growing rookery.
It is incredibly fortuitous that the refuge, dedicated to the protection of marine turtle nesting habitat, came along just as the turtles were poised to advance incrementally in abundance and survival status. Nothing is more critical to that advance than maintaining natural beaches: no sea walls, no foreign sand, no landscape alteration, no lights. That's the lay of the land of the Carr Refuge beach, and those features help support more than a million hatchlings that will enter the ocean from this beach each year. We would do well to emulate the conditions at the Carr Refuge, using it as a model for beaches statewide, and making preservation of natural qualities the goal of our coastal management programs.
What I have seen at the Carr Refuge provides an excellent window into what is happening with marine turtles throughout Florida. Here's a summary as the loggerhead nesting season ends and the Florida green turtle's season is about to close.
Of the three species, the population dynamics and survival status of loggerheads have been the most variable, and controversial, in recent years. We began to collect consistent data at Carr in the 1980s and documented about 9,300 loggerhead nests, with a modicum of variability, from 1982 to 1989. During the 1990s loggerhead nest production rose at a surprising rate, such that, by 1998, the total had essentially doubled, to 17,729 at Carr, nearly 100,000 statewide. But then the bottom fell out.
The loggerheads fell into what was generally described as "a steep and serious" decline, which lasted through 2004 or 2007, depending on interpretation of the data. The precipitous decline seen after 1998 drew the attention of governmental agencies, NGOs and the international marine turtle conservation community. While the causes of the decline are probably multiple and variably important, there is a rough consensus among authorities that incidental take of loggerheads by long-line, net and trawler fisheries in the North Atlantic was the primary cause. But it's not that simple. A basic tenet of ecology is "carrying capacity" — how many members of a species a particular habitat can support. Animals such as loggerhead turtles live so long that it's possible we simply don't understand their natural population swings.
One thing is clear. The "steep and serious" decline has leveled off, at least in the most recent four to six years. We logged 12,233 loggerhead nests at Carr in 2010, equivalent to 73,500 statewide and about 30 percent more than the number seen in the 1980s.
The 2011 loggerhead nesting season is nearly over, so we can confidently estimate that we will document about 11,000 loggerhead nests at the Carr Refuge — not as good as last year but still 18 percent above the level seen in the 1980s. Anything could happen, including another decrease in the numbers, but if the current trend persists for several more years, the statistics will allow us to call it a "reversal," not just a "leveling off."
The Florida green turtle
The really big story of the past two decades, at the Carr Refuge and elsewhere in Florida, is the recovery of the Florida green turtle. I believe it should be regarded as one of the great events in the history of wildlife conservation in North America. When our research group began systematic, seasonlong surveys of marine turtle nesting on this beach, we documented fewer than 50 green turtle nests on the 21-kilometer expanse, in each of the first three years (1982-1984). Compare that to the roughly 9,300 loggerhead nests on the same beach in those years. Clearly, the Florida green turtle was teetering on the brink of destruction in the late 20th century. In spite of the paltry nature of those numbers, this beach was recognized as the best green turtle nesting beach in the country, and that information was fed into the legislative process that led to the creation of the Archie Carr National Wildlife Refuge.
By about 1990 green turtles began to gain traction as the result of the protection afforded by the federal Endangered Species Act, to which they became subject in 1978. The numbers of green turtle nests grew exponentially through the '90s and the last decade to a degree rarely if ever matched in the annals of Threatened/Endangered Species Recovery. In 2010 we documented 4,095 green turtle nests at Carr and it is clear, now, that we will top 5,000 in 2011 (the season runs until early October).
Florida green turtles are participating in a global phenomenon. Milani Chaloupka, an Australian biometrician, has recently shown that two green turtle rookeries in Australia, the one at Ogasawara (Japan), the one at French Frigate Shoals (Hawaii) and the big one at Tortuguero (Costa Rica) are all increasing at about 3½ to 5½ percent a year. Such rates are extraordinary for wildlife populations of any kind, anywhere.
In the same paper Chaloupka determined the population growth rate at the Carr Refuge to be 13 percent per year and that figure has been confirmed by the FWC-FWRI scientists in St. Petersburg.
All over the world green turtles adhere to a biennial pattern of highs and lows in nest production. That is why it is so surprising that we are in the process of breaking the record for production in consecutive years. It has happened rarely, if ever, before. By the same token, we should not be shocked or surprised if green turtle nest numbers fall sharply in 2012. That would simply be adherence to an evolved feature of the phenology of the species.
It is worth noting here that our research group has also been studying the dynamics of the population of juvenile (immature) green turtles that inhabits the Indian River Lagoon, on Florida's east coast. We use capture rates (catch-per-unit-effort) as an index of population abundance. For nearly 30 years the slope of the line regressing abundance (catch rates) over time has been strongly positive. The two measures (nest production by adults on the beach and capture rates of juveniles in the lagoon), taken together, constitute strong evidence of the beginning, at least, of the recovery of the Florida green turtle.
The leatherback turtle
The story of the leatherback turtle in Florida needs to be told in the context of the species' survival status on a global scale. It is one of strong contrasts and disparate tendencies. Leatherbacks are the largest of the marine turtles. Most of those nesting in Florida weigh 700 to 900 pounds, although many secondary references say they reach three-quarters of a ton (1,500 pounds). They are bigger than loggerheads and green turtles by a factor of 2 or 3. The survival status of leatherbacks differs vastly in the Atlantic and Indo-Pacific.
Massive egg harvest on the four big Mexican Pacific nesting beaches and incidental take by long-liners, net fishermen and trawlers have reduced nest numbers (a measure of the size of the adult female population) from about 160,000 in 1980 to, perhaps, fewer than 1,000 today. Outright lawlessness on the beaches makes it difficult to get crucial data but aerial surveys have provided some insight. On the other side of the Pacific, nesting at the "big" beach at Terengganu, Malaysia, where many thousands nested in the past, has been decimated. The status of the leatherback in the Pacific is, quite simply, a train wreck.
Surprisingly, the plight of the leatherback in the Atlantic appears to be much improved. The major rookeries, in Guyana, Surinam, Trinidad, St. Croix and Panama are either quite stable or growing steadily. On the other side of the Atlantic, we have reliable reports of 40,000 nests on the beaches of the small coastal nation of Gabon, and good reason to believe that there are similar numbers on the beaches of several countries in that region.
Until recently the coast of Florida has been regarded as a relatively unimportant leatherback nesting ground but, apparently, the growth of leatherback numbers in the Caribbean is spilling over into Florida. Recently, record numbers of leatherback nests have been documented in our state every three or four years. Most of that increased nest production takes place in Palm Beach and Martin counties, especially in the Jupiter-Juno area.
During the first 15 years of our work at the Carr Refuge we saw virtually no leatherback nesting whatsoever. Then, in 1996, 10 clutches were deposited on the Carr beach, and the numbers have been rising ever since. With 52 as a maximum, the numbers still pale in comparison to the thousands of loggerhead and green turtle nests deposited there, but there is a persistent upward trend.
We recognize that the Carr Refuge is on the extreme northern margin of the leatherback nesting range and that, as the statewide population grows, the proportion occurring at Carr will probably remain at or slightly less than 5 percent. Nevertheless, the addition of these awesome creatures to the nesting assemblage at Carr adds a whole new dimension to the refuge and enhances its value as a conservator of our nation's wildlife heritage.
That the "steep and serious" decline, seen in the last decade, has bottomed out and leveled off, can be regarded as good news. That and the extraordinary trends in green turtle and leatherback survival status should gladden the heart of anyone interested in wildlife conservation in general, marine turtle conservation in particular.
Llewellyn M. Ehrhart is professor emeritus at the University of Central Florida.