Living Sanibel: Loggerhead sea turtle
By far the most common nesting sea turtle found in Southwest Florida, the loggerhead has been visiting the Gulf beaches since they were formed thousands of years ago. The loggerhead used to be much larger than is commonly found today. When Ponce de Leon arrived in Florida there were turtles weighing 1,000 pounds or more. A loggerhead of 600 to 800 pounds was quite common until the turn of the 20th century. Today, a loggerhead approaching 500 pounds is considered remarkable.
The range of the loggerhead is worldwide, though only in tropical or subtropical waters. There are still a couple of sites where up to 10,000 females nest every year: one is in South Florida and another in Oman at the tip of the Saudi Arabian peninsula. Approximately 68,000-90,000 loggerhead turtle nests are recorded in the United States every year. The world population of the species is unknown.
The loggerhead is an omnivore, eating jellyfish, Portuguese man o’ war (a toxic jellyfish the loggerhead is immune to), sponges, small fish, crustaceans, mollusks, crabs, and shrimp. Juveniles eat sea grasses and marine worms at first, moving to larger prey as their powerful jaws develop. The adult sea turtle has few natural predators. Sharks have been known to bite off turtle limbs but only an extremely large shark is capable of piercing the thick carapace.
The hatchlings are another story. Literally everything preys upon them for the first year of life, including raccoons, dogs, herons, seagulls, crows, birds of prey, ghost crabs, shorebirds, snook, catfish, tarpon, shark, and even fire ants. To counter this constant predation, the female loggerhead can lay as many as four or five clutches of eggs in a breeding season, which may occur only every two or three years. Every clutch holds between 50 and 150 eggs, which helps the species since the mortality rate of sea turtle hatchlings is precariously close to 100 percent. Studies have shown that only one out of every 1,000 sea turtles makes it to adulthood. Therefore, any additional pressure on its fecundity puts its long-term survival in jeopardy.
Once heavily preyed upon by humans, all the world’s sea turtles are now endangered. Illegal taking of mature turtles still occurs throughout much of its range. An even larger threat to the population comes from people raiding turtle nests for eggs. Finding a sea turtle nest is not difficult since the female hauls herself up beyond the surf line and leaves a clearly evident crawl track. Eggs are still taken illegally throughout much of the Third World. Roughly the size of a large Ping-Pong ball, the egg is a free source of protein in a hungry world.
Other leading causes of mortality for the loggerhead are long-line fishing and shrimp trawlers, which the turtle gets caught in and drowns. In 1989, the National Marine Fisheries Service required all U.S. shrimp boats to install turtle extruder devices (TEDs). These large metal contraptions allow turtles and larger fish to escape entanglement in the trawling net. TEDs have helped tremendously, but many shrimp fleets throughout the world refuse to install them, or in some instances they fail to work correctly because of improper installation.
Thousands of sea turtles also die annually from choking on plastic trash. To a sea turtle that feeds on jellyfish, a plastic bag or a six-pack ring floating offshore looks like food. Once ingested, this plastic can become lodged in the intestines, causing a slow and painful death. As if these gauntlets aren’t enough, still another cause of loggerhead mortality is boat and propeller collisions. This is especially true in the early spring when the loggerhead comes to the surface to mate. Because of these and other impacts, the loggerhead turtle has suffered a 40 percent decline in population in the past decade.
This is an excerpt from The Living Gulf Coast – A Nature Guide to Southwest Florida by Charles Sobczak. The book is available at all the Island bookstores, Baileys, Jerry’s and your favorite online sites.