- Marine biologists warn that the western Pacific leatherback could go extinct without immediate conservation measures and transnational cooperation.
- This subpopulation has decreased at a rate of 5.6% each year for an overall 80% decline over a 28-year period, according to a recent study.
- While the IUCN lists the species as a whole as vulnerable, the Pacific populations are critically endangered partly because of their long migratory routes through the high seas, where they face threats like drift gillnet fishing, ship strikes and pollution.
- The eastern Pacific subpopulation, which nests in Mexico and Central and South America, faces similar threats. Both populations are at high risk of extinction.
Clear-skied, low-wind summer days are rare off the coast of California. But they’re a blessing if you’re a researcher tracking down critically endangered leatherback sea turtles.
Marine ecologists Scott Benson and Karin Forney, with NOAA’s Southwest Fisheries Science Center, spent many of those days tag-teaming a decades-long research effort to collect data on one of the world’s oldest and largest marine reptiles. Forney sits in the clear belly of a NOAA surveying plane, scanning the dark waters like a hawk, notifying the team when she spots a leatherback sea turtle (Dermochelys coriacea). Benson, her husband, is among the scientists on the boat below, prepped at the hull with a large net, anticipating the moment they can heave the prehistoric giant on board.
Then comes the sampling: blood tests, tissue samples, attaching transmitters, recording weight. It’s an hour-long ordeal, Benson says, and “an all-consuming task.” In a month and a half, the team gets maybe five good-weather opportunities to collect data on this massive but little-understood species. And it could be their last chance to save this population.
The western Pacific leatherback sea turtle is at high risk of extinction, according to a study published in Global Ecology and Conservation. The researchers, including lead author Benson and co-author Forney, used roughly three decades of data to assess the population’s status. Combining their observations of foraging turtles in California with data on nesting patterns in Indonesia, the researchers estimate the population has declined at a rate of 5.6% annually, suffering an overall 80% decline from 1990 to 2017.
Both on land and at sea, the turtles face a series of existential threats in the Pacific. The situation is so dire that scientists on both sides of the ocean have dedicated their lives to reeling the distinct populations back from a dangerous tipping point.
The leatherback in the Pacific
The world knew little about Pacific leatherbacks prior to the 1980s, when scientists started collecting more data. Without modern-day technology like satellite transmitters to track turtles’ movements, biologists couldn’t have known that the leatherbacks foraging off the Californian coast were the same as those nesting in the western Pacific.
Today we know that leatherback sea turtles span the globe with seven genetically distinct subpopulations: the eastern and western in the Pacific Ocean, as well as three in the Atlantic Ocean and two in the Indian Ocean. While the IUCN lists the species as a whole as vulnerable, both Pacific subpopulations are considered critically endangered.
“We know what a thriving sea turtle population needs, but the expanse over which this drama is playing out in the Pacific is so huge, it’s hard to understand the whole puzzle and which parts need to be leveraged,” said Kyle Van Houtan, chief scientist of the Monterey Bay Aquarium, who was not involved with the study.
All leatherback sea turtle populations are declining, but those in the Atlantic and Indian Oceans are more robust than the plummeting Pacific populations, Benson said.
Pacific leatherbacks feed in seven known areas of the ocean, stretching from New Zealand to Japan to California. While the eastern subpopulation nests in Mexico and parts of Central America, western Pacific leatherbacks nest primarily in Indonesia, Papua New Guinea and Vanuatu.
The research team recorded an average of 140 individuals in central California’s foraging patch from 1990 to 2003, but that number dropped to an average of 55 by 2017.
Still, the data only account for a fraction of a population that is scattered across the entire Pacific Ocean and migrates at unpredictable time intervals. Benson said the annual decline of nesting females in West Papua, Indonesia, closely mirrors the rate of decline his team calculated in California, providing further evidence that the entire western subpopulation is suffering.
There is no exact count of how many western Pacific leatherback turtles are left. An analysis in 2013 by the IUCN estimated around 1,400 adult turtles survived in the subpopulation. The IUCN also forecasts the population will dip below 1,000 individuals by 2030.
Scientists say a concrete population estimate is difficult given the nature of western Pacific leatherbacks. It is the only subpopulation with a bimodal nesting pattern, meaning some females nest in the summer while others nest in the winter. Compounding the uncertainty, western Pacific leatherbacks only visit foraging and nesting grounds every two to five years.
Western Pacific leatherbacks are attracted to the Monterey ecosystem in California due to the “the immense productivity … because of the upwelling, the deep offshore currents coming up to the surface, causing these cascades of nutrients and life,” Van Houtan said. “That’s why we have these leatherbacks.”
Unlike most reptiles, leatherback turtles can self-regulate their body temperature, allowing them “to go places where no other sea turtles can go,” Van Houtan added. These long-evolved marine reptiles — “living fossils,” as he describes them — date back to the Cretaceous Period, when dinosaurs roamed the Earth. Today, they are the only living species in the Demochelys genus.
Weighing up to 900 kilograms (2,000 pounds) and growing up to 2 meters (7 feet) long, leatherbacks are the largest turtle species on the planet. They are also the most migratory sea turtle, traveling up to 16,000 kilometers (10,000 miles) a year between nesting and feeding sites. These giants can dive more than 1,200 m (4,000 ft) deep — deeper than any other sea turtle — thanks to their soft shells, which won’t crack under pressure.
But even evolution’s long helping hand may not be enough to protect them from humanity’s reach.
Threats at sea and on land
Pacific leatherback turtles face a multitude of perils both at sea and on land. Among them are impoverished villagers who poach eggs or adults for meat, and habitat degradation in the Pacific islands, where coastal development and cyclones have eroded nesting beaches. But the biggest threat, according to scientists, are fishing vessels that accidentally kill turtles as bycatch.
Drift gillnet and longline fisheries — large-scale fishing operations on the open ocean that harvest an abundance of seafood, like swordfish — are notorious for killing sea turtles that get caught in nets and other fishing gear. Worse, scientists say existing bycatch data probably underestimate the true numbers.
“It’s the wild west out on the open ocean,” said George Shillinger, a marine biologist who has studied leatherbacks for three decades and is executive director of Upwell, an NGO dedicated to sea turtle conservation. He added that even if nests are protected, ship strikes and bycatch will continue to decimate the population. And then there’s the further obstacle of subsidized fisheries, expanding fishing fleets and more intense artisanal fishing, he said, noting “we are really challenged to stave off the relentless pressures.”
Across the Pacific, marine scientist Deasy Lontoh champions for leatherback protection in West Papua, Indonesia. She is the research coordinator for the Abun Leatherback Project, which seeks to combat threats that are difficult and costly to mitigate at sea by protecting what’s on shore: nesting females and eggs.
Lontoh co-authored a recent paper outlining threats to the largest remaining nesting population on two beaches in West Papua, known as Jamursba-Medi and Wermon. Lontoh’s team says it hopes to protect at least half of leatherback nests with the help of local communities.
Lontoh is trying to avoid what happened in Malaysia when a nesting population of western Pacific leatherbacks vanished entirely. Egg harvesting was a rampant, and legal, way for locals to make money until the Terengganu Turtle Sanctuary Advisory Council outlawed it in 1988. From the 1950s to 1995, Malaysia went from 10,000 nests annually to a mere handful. No nests have been reported in almost a decade.
But even when people don’t harvest turtle eggs, juvenile survival is naturally a gamble. Scientists estimate that only one in every 1,000 eggs survive to maturity, while females lay around 80 eggs in each nest.
“A lot of hatchlings will die, so we just need to produce high enough numbers … and assume that some of them will become adults in 15 or 20 years,” Lontoh said.
Climate change further mars the leatherbacks’ future. More extreme storms can decimate nesting sites, while rising temperatures can bake eggs to death. Lontoh said that, locally, sands can reach a lethal 33° Celsius (91° Fahrenheit), and temperatures are rising in the area alongside global trends.
Under normal circumstances, leatherbacks would be less fragile, Benson notes. For one, they lay eggs in multiple locations and span much of the world’s oceans. They have also survived several natural climate changes over the past 80 million years. But scientists don’t know how the recent, and rapid, changes in water temperature, ocean currents, and upwelling of nutrients will affect leatherbacks.
“Climate change is thrusting all of those things that they depended on up into the air,” Van Houtan said. “We need to listen to these signals that the ocean is telling us, because the ocean is the driver of life on our planet.”
As the Pacific leatherback population size continues to shrink, climate change and human pressures become a daunting threat to their survival.
“Something more needs to be done,” Shillinger said.
Turtle needs: Regulations and tourism
For a species inhabiting millions of square miles, keeping it out of harm’s way is a monumental task. Scientists have spent the past two decades calling for stricter fishing regulations. But the lack of transnational cooperation and enforcement by governments has been an obstacle to protecting the turtles through policy and regulations.
“One government won’t solve it,” Shillinger said. “Everyone’s got to be involved.”
By the mid-1990s, emerging data revealed high bycatch rates for large marine animals like sea turtles. To mitigate bycatch, the U.S. government created the Pacific Leatherback Conservation Area in 2001: a seasonal protected area off the U.S. West Coast that covers 650,000 square kilometers (250,000 square miles) of ocean and prohibits drift gillnet fishing during the months leatherbacks feast on jellyfish.
Dubbed a “time-area closure,” the new regulation helped reduce leatherback bycatch from an average of about 15 turtles per year to fewer than two a year after 2001, according to NOAA.
Additional regulations have helped save turtles in U.S. waters. For example, California’s commercial fisheries aren’t allowed to use pelagic longlines that can accidentally bait sea turtles. Meanwhile, Hawaiʻi’s longline fishery comes with 100% observer coverage, meaning there is always someone documenting bycatch. California is also testing newer technology like deep-set buoy gear, which bypasses leatherbacks feeding on jellyfish to hook swordfish at lower depths.
However, none of these rules apply in international waters. For better protections, Benson and Forney say member countries of regional fishery management organizations like the Inter-American Tropical Tuna Commission need to encourage safer fishery practices.
For the leatherback populations to recover, scientists have suggested a 40% bycatch reduction over the next two decades.
It’s an ambitious goal, Shillinger said, adding “what really has to happen is to elevate political will … and make governments accountable for protecting their resources.”
In the meantime, Benson called on people to ask waiters at restaurants how and from where their fish is sourced.
“Please consume U.S.-caught swordfish or tuna, because it comes with a side dish of Endangered Species Act rather than a side dish of dead turtle or dead dolphin,” he said.
Leatherback conservation also needs to move forward at nesting sites. The Abun Leatherback Project, which works primarily in remote and impoverished villages in West Papua, attempts to protect western Pacific leatherbacks by employing the help of locals. A team of 10 monitors patrols the beaches while others help measure leatherbacks, release hatchlings or create shades made from palm fronds to keep nests cool.
Conservation success is contingent upon local people, Lontoh said: if they don’t care about leatherbacks, they won’t try to save them.
“[Locals] have strategic roles,” Lontoh said. “In the future, they’re probably the ones who will [either] help take care of the leatherbacks or help them go extinct.”
But that requires incentives and income. Lontoh said the local government set forth an agenda in 2019 to develop the nearby area for tourism. In rural areas with limited resources, women have prepared to make souvenirs, such as the traditional noken woven bags, to sell to tourists.
“To get [rural people] to see that the leatherbacks are worth protecting, they need to feel benefits from conservation,” Lontoh said.
Tourism has funded conservation efforts in other areas of the world already, Shillinger said.
“Leatherbacks bring in a lot of ecotourism projects around the world,” he said. “Turtles are really charismatic, benign, attractive animals, and no one wants to see them harmed. So culturally, economically and socially, turtles play an important role.”
An ocean without leatherbacks
The question remains: What if western Pacific leatherbacks do go extinct? Scientists warn it could happen in a matter of decades without immediate action.
“In the West Pacific, there’s a little bit of a window left, but it’s not much,” Benson said. “It’s definitely 11:55 on its way to midnight.”
Losing leatherbacks could throw the entire ecosystem off-balance. Leatherbacks, with their ferocious appetites (eating up 40% of their body weight daily), gobble down huge amounts of jellyfish that in turn devour fish larvae and plankton. By eating these bountiful yet low-nutrition “jellies,” the turtles help keep jellyfish numbers under control. In recent years, however, Benson said he’s noticed an increase of brown sea nettle (Chrysaora fuscescens), one of the leatherbacks’ favorite jellies, in California’s waters.
“Over time, this might be an illustration that the number of leatherbacks is so reduced now that they can’t serve part of their ecological roles,” Lontoh said.
Because jellyfish eat fish larvae, more jellyfish may mean less fish overall, likely impacting small-scale artisanal fisheries and rural Pacific islanders who depend on fish for food or income. Fish provide about 3.3 billion people worldwide with nearly 20% of their animal protein, according to the most recent Fishery and Aquaculture Statistics report from the Food and Agriculture Organization of the U.N.
A world without leatherbacks “would still function,” Shillinger said, “but there would be some big shifts that we still don’t understand.”
As the forces of climate change are amplified — cyclones that wash away nests, sand temperatures so hot that hatchlings bake to death, a rapidly changing California Current — a conservation biologist’s job becomes no easier.
“This is kind of a higher calling,” Benson said. “This is a species threatened with extinction, a lot of people don’t know about it, so it’s my job to provide some data to increase the opportunities for recovery of the population.”
Ironically, Shillinger said, many Californians are unaware that their state marine reptile is the Pacific leatherback.
“Losing a species is a tragedy, something that humanity should really be concerned about,” Shillinger said. “As the turtles go, so too does everything else — including ourselves.”
Citations:
Benson, S. R., Eguchi, T., Foley, D. G., Forney, K. A., Bailey, H., Hitipeuw, C., … Dutton, P. H. (2011). Large-scale movements and high-use areas of western Pacific leatherback turtles, Dermochelys coriacea. Ecosphere, 2(7), 1-27. doi:10.1890/ES11-00053.1
Benson, S. R., Forney, K. A., Moore, J. E., LaCasella, E. L., Harvey, J. T., & Carretta, J. V. (2020). A long-term decline in the abundance of endangered leatherback turtles, Dermochelys coriacea, at a foraging ground in the California Current Ecosystem. Global Ecology and Conservation, 24, e01371. doi:10.1016/j.gecco.2020.e01371
Spotila, J. R., & Tomillo, P. S. (2015). The Leatherback turtle: Biology and conservation. JHU Press.
Carretta, J. V., Moore, J. E., & Forney, K. A. (2019). Estimates of marine mammal, sea turtle, and seabird bycatch from the California large-mesh drift gillnet fishery: 1990-2017. NOAA Technical Memorandum, U.S. National Marine Fisheries Service. doi:10.25923/s650-dd93
Eckert, K. L., Wallace, B. P., Frazier, J. G., Eckert, S. A., & Pritchard, P. C. H. (2012). Synopsis of the biological data on the leatherback sea turtle (Dermochelys coriacea). U.S. Department of Interior, Fish and Wildlife Service, Biological Technical Publication BTP-R4015-2012, Washington, D.C.
Jones, T. T., Bostrom, B. L., Hastings, M. D., Van Houtan, K. S., Pauly, D., & Jones, D. R. (2012). Resource requirements of the Pacific leatherback turtle population. PLOS ONE, 7(10), e45447. doi:10.1371/journal.pone.0045447
Liew, H. C. (2011). Tragedy of the Malaysian Leatherback Population. In Conservation of Pacific Sea Turtles (pp. 97-107). University of Hawaii Press.
National Marine Fisheries Service and U.S. Fish and Wildlife Service. 2020. Endangered Species Act status review of the leatherback turtle (Dermochelys coriacea). Report to the National Marine Fisheries Service Office of Protected Resources and U.S. Fish and Wildlife Service.
Pakiding, F., Zohar, K., Allo, A. Y., Keroman, S., Lontoh, D., Dutton, P. H., & Tiwari, M. (2020). Community engagement: An integral component of a multifaceted conservation approach for the transboundary Western Pacific leatherback. Frontiers in Marine Science, 7, 756. doi:10.3389/fmars.2020.549570
Banner image: A leatherback hatchling makes its way to the water on a beach in Indonesia. Image by Faris Luthfi.
April 30, 2021 at 06:08PM
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