There are seven species of sea turtles on Earth: green turtle, leatherback, flatback, loggerhead, hawksbill, Kemp's ridley, and olive ridley. Sea turtles typically live between 30 and 50 years, with some documented cases of sea turtles living as long as 150 years. While we know that all sea turtle species have lengthy lifespans, the upper limit of their potential natural lifespan remains a mystery to scientists.
Of the seven species of sea turtles on the globe, the hawksbill has the shortest lifespan at 30 to 50 years, and the green turtle has the longest at 80 years or more. The largest and smallest sea turtles-the leatherback and the kemp's ridley, respectively-both have an average lifespan of 45 to 50 years.
The Sea Turtle Life Cycle
A sea turtle's life begins when a female nests and lays eggs on a beach, usually near where she was born. She will nest between two and eight times each season, laying about 100 eggs in each nest. The eggs are vulnerable to predators like birds, mammals, and fish. After a period of six to eight weeks, the surviving hatchlings break out of their eggs (called "pipping"), emerge from the sand, and head towards the water.
Only an estimated 1 in 1,000 to 1 in 10,000 hatchlings survive to experience the next phase of life: the open ocean phase. This period, which lasts between two and 10 years, is also called “the lost years” because the turtles' movements at sea are hard to monitor. While turtles can be tagged by scientists, the transmitters used are often too bulky for younger creatures. In 2014, a group of researchers from Florida and Wisconsin used smaller equipment to track the “lost years” of hatchlings that they had raised for several months and then released. They concluded that hatchlings head out to sea to avoid predators and follow warm surface waters that support their growth.
Sea turtles grow up slowly. It takes them between 15 and 50 years to become reproductively mature. They spend their adult lives foraging in coastal waters and migrating to beaches to mate. Only the females come ashore to nest, a process that takes place every two to five years.
Like birds and fish, sea turtles rely on the magnetic field of the planet to return to their place of birth. Their migrations can be lengthy. In 2008, a leatherback was tracked traveling 12,774 miles from Indonesia to Oregon. Females have been known to nest until the age of 80.
Sea turtles often die because of predation and human-related causes. Some of their main predators are sharks, killer whales, and large fish like grouper. They also face dangers from poaching, fishing gear entanglement, pollution, marine debris like plastic, and climate change. Rising sea levels and increasing storm activity threaten nesting grounds. Due in large part to these human-made threats, most sea turtle species are endangered.
How Long Can Sea Turtles Live?
The title of “oldest sea turtle” remains unclaimed, which enhances the species' mystique. Determining exactly how long sea turtles live is particularly difficult because the turtles often outlive the duration of most studies. When sea turtles are tagged, satellite data transmission typically lasts just between six and 24 months. Meanwhile, turtles can live for decades.
To make matters even more ambiguous, there is no scientifically accepted method for using a sea turtle's appearance to determine its age. Scientists often analyze the bone structure of deceased turtles to estimate age.
One of the oldest known sea turtles is a green turtle named Myrtle, who has been at the Cape Cod aquarium for more than 45 years and is estimated to be 90 years old. However, according to Carol Haley, the Assistant Curator of Fishes at the Tennessee Aquarium, some sea turtles can live 100 or even 150 years.
A few sea turtles may have outlived that estimate in the last few decades. In 2006, Li Chengtang, head of the Guangzhou Aquarium in China, said that the oldest sea turtle onsite was “about 400 years old, as determined by a shell test by a taxonomic professor.” Another news report of an elderly sea turtle in the Philippines stated that a sea turtle close to 200 years old was discovered in a fish pen and brought to the Bureau of Fisheries and Aquatic Resources.
Why Do Sea Turtles Live So Long?
Sea turtles have been on Earth for more than 100 million years. To put that in perspective, dinosaurs went extinct about 65 million years ago and early human ancestors started walking on two legs about 4 million years ago.
Research indicates that a key explanation for the sea turtle's long lifespan is its slow metabolism or rate of converting food into energy. According to a 2011 study in the Journal of Experimental Biology, metabolic rates play a key role in sea turtle health, as they control “the fitness of the individual” and “ultimately define population structure and size." Animal metabolism is sometimes described as “the fire of life.” Typically, the slower the burn, the longer a fire-or creature-lives. Sea turtles metabolize and grow slowly, and consequently live for a longer period.
Green sea turtles can slow their heartbeats down to a rate of 9 minutes between beats. This characteristic empowers them to take drawn-out feeding dives for up to five hours. In stark contrast, a speedy hummingbird's heart beats as many as 1,260 times each minute, and it may eat every 10 minutes. Hummingbirds have a much shorter life span than sea turtles, living just three to five years.
While sea turtles continue to face numerous threats, scientists and researchers won't be deterred. Conservation efforts persist to keep these majestic divers pushing the limits of long life in the sea.
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