The Tortuga Triangle

By Lenihan, Daniel J | Natural History, April 1997 | Go to article overview
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The Tortuga Triangle


Lenihan, Daniel J, Natural History


His stories were what frightened people worst of all. Dreadful stories they were; about hanging, and walking the plank, and storms at sea, and the Dry Tortugas.

Robert Louis Stevenson, Treasure Island

Lying in the Gulf of Mexico at its juncture with the Atlantic Ocean and Caribbean Sea, the Dry Tortugas were discovered by Ponce de Leon in 1513. "They reached the chain of islets which they named Tortugas [turtles]," wrote the Spanish historian Antonio de Herrera, "because in a short time of the night they took, in one of these islands, a hundred and seventy turtles, and might have taken many more if they wished, and also they took fourteen seals [probably the Caribbean monk seal, extinct since the 1950s], and there were killed many pelicans and other birds, of which there were five thousand." Then as today, however, these islets of sand and coral rubble would not have yielded fresh water with which to wash down such bounty. Hence the "Dry" appellation, subsequently attached as a caution to mariners.

With a combined terrestrial surface area of forty acres, the Dry Tortugas barely merit a pinpoint on a map, but their atoll-like configuration, covering 75,000 acres of reefs and shallows, makes them a natural ship trap. The site of more than 250 marine disasters from the early 1600s through the twentieth century, their waters harbor the half-buried remains of Spanish galleons and the hulks of iron-hulled clippers. The study and preservation of this archeological resource has been the focus of my long-standing involvement with the Dry Tortugas. But it is by no means their only historic attraction. In the nineteenth century, the Dry Tortugas's shifting sands were made to bear the weight of Fort Jefferson, probably the largest masonry structure in the Western Hemisphere.

Besides being a touchstone to the past, the Dry Tortugas are a laboratory for the study of coral and other marine life, since they are far enough from agricultural and industrial runoff to serve as a "control" for ecological changes. And, lying in the path of major bird migration routes, they have been a protected bird preserve and breeding ground since 1908. Blue-footed boobies, sooty terns, noddies, herons, egrets, gulls, brown pelicans, cormorants-all call the Dry Tortugas home for at least part of the year. Frigatebirds glide majestically, preying on fish and occasionally on the nests of other birds. In stark contrast, migrating cattle egrets (a species introduced into the New World from Africa) stagger about Fort Jefferson's parade ground in a macabre dance of death from starvation owing to a dearth of appropriate insects to feed on. They cluster about a freshwater fountain that serves only to prolong their agony.

John James Audubon visited the Dry Tortugas in 1832, noting that the colonies of sooties and noddies were heavily exploited for food by "eggers" from Havana. He also noted that the eggs (and birds) were extremely good eating and much enjoyed by the crew of the government vessel that carried him. (The great naturalist and painter who practiced ornithology through the barrel of a gun was no sentimentalist when it came to obtaining specimens for his paint palette or his soft palate.)

I first visited the Dry Tortugas in 1974 as the National Park Service observer on a project under the field direction of Larry Murphy, then an underwater archeologist for the state of Florida. For the first seven days of my ten-day stay, we were buffeted by gale force winds, and cabin fever drove us to less than judicious behavior. When the wind died down one night, we headed off at 1:00 A.M. on diver propulsion vehicles to see if there were any large sharks swimming in the entrance channel (exercising a type of logic that has helped screen gene pools from time immemorial). During this escapade, I almost smashed my scooter headlight into the cascabel of an eighteenth-century cannon. Within an hour we were setting buoys and taking measurements; the abundance of shipwrecks had conspired to make our early morning joy ride into a working dive.

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