Imagine a sea turtle crossing the Pacific Ocean, travelling thousands of kilometres from tropical waters to the coast of the United States. This is the journey of the Pacific leatherback turtle (Dermochelys coriacea), the world’s largest sea turtle, which forages far from the beaches where it nests.
Interestingly, California designated the species as its official state marine reptile in 2012. Yet one of the most important beaches where leatherbacks lay their eggs lies on the Bird’s Head Peninsula in Papua, Indonesia.
How does this turtle connect two regions so far apart?
A Journey That Begins on Papua’s Beaches
Female leatherbacks return to shore to lay their eggs. In Papua, two important nesting beaches are Jamursba Medi and Wermon, located in Abun District, Tambrauw Regency, Southwest Papua. Indigenous communities in the area know the beaches as Jeen Yessa and Jeen Syuab.
The area plays a major role in the leatherback population. A study published in the journal Ecosphere estimated that the Bird’s Head Peninsula accounts for around 75% of all leatherback nests in the western Pacific.
The two beaches were later combined into the Jeen Womom conservation area in 2015, covering 32,250.86 hectares. The government designated it a Coastal Park on 22 December 2017.
But nesting beaches are only one part of a leatherback’s life. After laying their eggs, female turtles return to the sea and can travel vast distances in search of food.
Crossing the Pacific in Search of Jellyfish
Leatherbacks do not spend their entire lives near the beaches where they hatch or nest. Another study published in Ecosphere, which tracked 126 turtles by satellite between 2000 and 2007, found that they travel to different parts of the Pacific Ocean depending on the nesting season.
Some turtles from the western Pacific head towards the California Current, off the west coast of North America. The journey can take 10–12 months and cover up to 11,400 kilometres.
What draws leatherbacks so far from tropical shores? The answer is jellyfish, one of their main food sources.
The California Current is a productive marine region because winds bring cold, nutrient-rich water from the ocean depths to the surface. This process, known as upwelling, supports marine life, including the jellyfish that leatherbacks feed on.
In central California, water temperatures of around 14–16°C support dense aggregations of jellyfish, including Chrysaora fuscescens and Aurelia. Leatherbacks typically forage in the area from early summer to late autumn, when water temperatures reach their annual peak and jellyfish are abundant.
They then begin leaving these waters as temperatures drop in October and November.
Although jellyfish can be abundant, they contain relatively little energy. Leatherbacks are therefore estimated to need to consume food equivalent to 20–30% of their body mass each day. A reliable supply of prey in particular locations helps explain why the turtles travel such long distances.
They also tend to return to the same feeding grounds. Of 11 tagged turtles with sufficiently long tracking records, all returned to central California waters the following year or later, while nine returned the following summer.
The importance of this region has also been recognised by the United States government. In January 2012, the National Marine Fisheries Service designated around 108,558 square kilometres of waters off California, Oregon and Washington as critical habitat for leatherback turtles. The availability of jellyfish was identified as one of the habitat’s important features.
Some journeys extend even farther. One female turtle from Jamursba Medi travelled at least 20,558 kilometres over 647 days of satellite tracking, eventually reaching Oregon before its signal disappeared.
From Seasonal Visitor to California’s Official Marine Reptile
The leatherback’s connection to California goes beyond its search for food. In 2012, California Assembly Member Paul Fong introduced Assembly Bill 1776 to designate the Pacific leatherback turtle as the state’s official marine reptile.
The Turtle Island Restoration Network sponsored the bill, with support from organisations including the Monterey Bay Aquarium and Oceana.
In its analysis, a California Assembly committee described the leatherback as a species that had remained virtually unchanged for around 150 million years and undertaken one of the longest migrations among reptiles.
Fong said the designation aimed to recognise the species’ importance to California while drawing attention to the threats it faces.
The bill passed and became law in 2012. Beyond granting the turtle official status, the legislation encouraged schools to teach students about leatherbacks, supported the development of a volunteer network to report sightings, and promoted cooperation with island nations in the western Pacific.
The designation also highlights the ecological connection between Asia and California. Leatherbacks that forage off the United States originate from western Pacific breeding populations that nest in Indonesia, Papua New Guinea and the Solomon Islands.
A Long-Distance Traveller Facing Growing Threats
Despite their ability to travel thousands of kilometres, leatherbacks face serious threats. At Jamursba Medi, the annual number of nests fell from around 14,522 in 1984 to 1,596 in 2011, a decline of approximately 78.3% over 27 years.
The decline was also evident at Wermon. Nest numbers there dropped from 2,994 in 2002 to 1,096 in 2011, a decrease of 62.8%. Combined, the two beaches experienced an average annual decline of 5.9% in nest numbers from 1984 onward.
A 2020 assessment by NOAA Fisheries estimated that the western Pacific leatherback population consisted of around 1,277 nesting females. Meanwhile, the number of leatherbacks in waters off the western United States had declined by around 80% since 1990.
The leatherback’s journey shows that marine wildlife does not stop at national borders. The nesting beaches of Papua and the feeding grounds off California are part of the same life cycle.
Protecting these turtles means safeguarding both habitats so they can continue to sustain the species’ remarkable journey across the Pacific.
