The Hawaiian Green Sea Turtle, known locally as honu, is an iconic fixture in the islands’ marine environment. Determining the exact age of any wild marine animal is difficult for scientists, especially for species that migrate across vast distances and live for many decades. Since they spend the majority of their lives in the open ocean, direct, long-term monitoring of a single individual from birth to death is virtually impossible.
Estimated Lifespans of Hawaiian Species
The most common and well-studied sea turtle in the region, the Hawaiian Green Sea Turtle (Chelonia mydas), is estimated to live for 60 to 80 years in the wild. Some experts suggest the oldest individuals may reach a century of life. The honu’s slow pace contributes to this extended longevity, as sexual maturity typically occurs between 25 and 40 years old.
Hawaiian waters are also home to other species, though they are observed less frequently than the honu. The Hawksbill Sea Turtle (honuʻea), a rare resident, is estimated to have a lifespan exceeding 50 years, reaching maturity between 20 and 35 years of age. Less common visitors include the giant Leatherback, which may live for over 90 years, and the Loggerhead and Olive Ridley turtles, with estimated maximum lifespans around 63 and 54 years respectively. These estimates are often based on newer, non-invasive techniques that analyze the species’ genetic makeup.
Measuring Longevity in Sea Turtles
Scientists rely on indirect methods to estimate sea turtle age and growth rates. The most traditional technique involves tagging and recapture, where researchers attach unique metal or passive integrated transponder (PIT) tags. Monitoring growth between capture events allows for the creation of growth curves used to model the age of the wider population. However, this method only provides a minimum age for turtles that are already adults.
A more precise technique is skeletochronology, which involves examining growth rings found in cross-sections of certain bones, similar to counting tree rings. These rings, called “Lines of Arrested Growth” (LAGs), are deposited annually and provide an accurate age for a deceased turtle. Newer, less-invasive methods are being developed, such as analyzing the rate of DNA methylation in the turtle’s genome. This innovative approach functions like a molecular clock, helping to predict the maximum potential lifespan of different species.
The Journey from Hatchling to Adulthood
A sea turtle’s life begins in a nest buried on a sandy beach. After hatching, the turtles emerge, usually under the cover of darkness, and scramble toward the ocean, guided by instinct toward the brightest horizon. Once in the water, they begin the “lost years,” a stage lasting four to ten years where their movements are largely unknown as they drift in open ocean currents.
During these pelagic years, young turtles are carried by ocean gyres, relying on floating mats of seaweed and debris for shelter and food. Mortality is high during this phase, with only a small fraction of hatchlings surviving to reach the juvenile stage. They eventually return to coastal waters, such as the reefs and bays of the main Hawaiian Islands, to forage. It takes decades for them to accumulate the energy reserves necessary to reach sexual maturity and begin the reproductive cycle.
Anthropogenic and Natural Factors Limiting Lifespan
Few Hawaiian sea turtles reach their maximum age due to natural and human-related threats. Natural predation, primarily by tiger sharks, remains a danger, especially for juveniles and sub-adults in nearshore foraging areas. However, human activity is the main factor that shortens the lives of these animals.
Human-Related Threats
Human-related threats include:
- Fibropapillomatosis (FP), a debilitating disease causing tumors widespread in the Hawaiian Green Sea Turtle population.
- Entanglement in discarded fishing gear, known as “ghost nets,” and the ingestion of plastic debris, which cause severe injury and fatal internal blockages.
- Boat strikes in popular nearshore waters, which are a significant source of trauma and death for basking and feeding turtles.
- Climate change, which poses a long-term threat by eroding nesting beaches and skewing the sex ratio of hatchlings, as warmer sand temperatures produce more females.