Last updated: March 13, 2024
Article
Despite Heroic Efforts, Kemp’s Ridley Sea Turtles Remain Critically Endangered
A seashore’s extraordinary work to rescue Kemp’s ridley sea turtles from extinction is holding the line for this ancient species. But their numbers are still too low to reclassify them as “threatened.”
Image credit: NPS
The gusty northern wind whips across the beach while I kneel in the sand next to a female Kemp’s ridley, the most critically endangered sea turtle species in the world.
It’s taken her 20 minutes to emerge from the Gulf of Mexico, crawl to the base of the dunes, and dig an 18-inch-deep lightbulb-shaped hole in the sand. As she begins to drop her round, white eggs into the nest, I see a bright glint of sunlight reflecting off metal. There’s a shiny silver identification tag dangling from her front left flipper. We’ve met this turtle before!
Padre Island National Seashore, located in Corpus Christi, Texas, is crucial nesting habitat for Kemp's ridley sea turtles. The seashore is the site of a 45-year program to form a secondary nesting colony as a safeguard against extinction of this ancient species, which nests primarily in Tamaulipas, Mexico. After many decades of intensive conservation, more Kemp’s ridley nests are found at Padre Island National Seashore—nearly 55 percent of all U.S. nests—than at any other U.S. location. The 2009 revision of the bi-national Kemp’s ridley recovery plan predicted that this work would lead to species recovery, allowing the U.S. Fish and Wildlife Service to downlist the species to threatened status by 2020. But this didn’t happen, and the seashore’s critical role in species recovery is more important than ever.
How Scientists Keep Track of Sea Turtles
Padre Island collaborates with partners in Mexico and Texas to obtain species-specific data. Land and wildlife managers use these data to take sound, science-based actions to protect the Kemp’s ridley population. Mary Kay Skoruppa is a biologist and the Texas coast sea turtle coordinator for the U.S. Fish and Wildlife Service. “The U.S. Fish and Wildlife Service depends on the scientific research conducted by Dr. Donna Shaver and her staff at the national seashore,” she said. “[Their work] directly aids in assessing critical habitat, consulting on federally funded or permitted projects, and tracking progress on species recovery.”
Image Credit: NPS
Biologists like me, who work for the seashore’s Division of Sea Turtle Science and Recovery, use mark-recapture tagging to document and identify nesting sea turtles. Metal tags often fall off during mating, migration, or when the turtle swims through debris. For this reason, we have to apply multiple tags to make sure the turtle retains at least one.
Image Credit: NPS
Every time a biologist encounters a new nesting female, we mark her by applying three identification tags to the turtle’s flippers. Using a hypodermic needle, we insert one passive integrated transponder (PIT) tag about the size of a grain of rice into the turtle’s front flipper. We also apply one-inch metal tags to the edge of the turtle’s front and rear flippers.
Once the turtle loses a flipper tag, a small scar remains, called a tag scar. We can also use this to figure out if the turtle is a recaptured female.
When we find a turtle nesting on the beach, we inspect her flippers for metal tags. We also use an electronic scanner to detect whether she has a PIT tag. Once the turtle loses a flipper tag, a small scar remains, called a tag scar. We can also use this to figure out if the turtle is a recaptured female. Usually, tag scars appear as small notches in the trailing edge of the turtle’s flipper. PIT tags have a very long retention time, often decades, but you need a specialized scanner to detect them.
A sea turtle with a large, very noticeable tag scar on the right flipper or a large white spot on the carapace (top shell) means the animal was part of a separate, multi-agency project. Those turtles were tagged as yearlings and released in the 1980s–2000s. Despite their larger size, the flipper scars do not impede the turtle’s movement.
A Fleeting Impression
Finding nesting Kemp’s ridley turtles can be difficult. At around 100 pounds, they are the smallest sea turtle species. Consequently, flipper impressions left in the sand are very shallow and quickly blown away by gusts of wind. The turtles’ tan coloration helps her blend in with the sand dunes. The 70-mile-long beach, remote location, and changing environmental conditions also make it difficult for scientists to find nesting females and nests. But the seashore’s Division of Sea Turtle Science and Recovery aims to intercept every female that comes to the park to nest. To accomplish this, dedicated biologists patrol the beach repeatedly from sunrise to sunset.
Image credit: NPS
Although they successfully tag many females, sometimes patrollers only find the tracks left behind by a turtle that already nested. Scientists use kinship analysis to match these nests genetically to known females identified through PIT or metal tags. Nesting females and nests can escape detection when environmental conditions obscure all evidence of their tracks and nest sites. In these instances, the female is never identified, and no samples are collected for kinship analysis. To limit this occurrence, biologists work together to patrol in a uniformly spaced pattern before all evidence is blown away. They visibly scour the beach for signs that a turtle has emerged from the sea to lay eggs.
The Long Game
Padre Island National Seashore has the only long-term, continuous, mark-recapture study of nesting Kemp’s ridley sea turtles in the world. These data have become a barometer for the species. Although many more turtles nest in Mexico, comprehensive mark-recapture efforts are no longer possible there. There are just too many turtles and too little funding and staff to tag them all. Yet continuous mark-recapture studies are essential for knowing how the species is doing. They allow researchers to understand long-term trends in parameters like the size of the nesting population and the number of females that return to the nest each year. Changes in reproductive trends can be the first indicator of a population-wide problem. Detecting these signals early could make a huge difference in whether or not this critically endangered species survives.
Image Credit: NPS
Sea Turtle Science and Recovery Division Chief Donna Shaver is the leading Kemp’s ridley authority in the United States. In her 42-year career with the National Park Service and the U.S. Geological Survey, she has championed conservation, research, and public education to support sea turtle recovery. Under Shaver’s leadership, the park’s Kemp’s ridley nest-protection program has flourished and gained international recognition. Shaver and her staff have authored 75 percent of the peer-reviewed, scientific journal articles about wild sea turtles in Texas. Most of these were about Kemp’s ridley turtles.
“The Kemp’s ridley nesting population in Texas has dramatically increased over the last forty years as a result of this program, but many threats still exist today, and a few, such as climate change, are getting worse.”
”Endangered species conservation is the long game,” said Shaver. “The Kemp’s ridley nesting population in Texas has dramatically increased over the last forty years as a result of this program, [but] many threats…still exist today, and a few, such as…climate change, are getting worse. Protecting the nesting females and their nests…are still key to making sure the population can recover.”
Recovery Remains Elusive
After years of work, Kemp’s ridley nesting has increased in both Texas and Mexico. But nesting numbers are still below levels needed for species recovery. Shaver’s unpublished data show that annual numbers of nests found in Mexico and Texas have recently diverged, likely due to differences in nest management. Initially, scientists relocated all Kemp’s ridley nests in Mexico for protected incubation. But starting in 2004, researchers left a subset of nests there to incubate in situ—unprotected, on the beach. This was because it was impossible to safely move all the eggs laid during large “arribadas” (synchronous nesting days).
Image Credit: NPS / Sue Wolfe
Inside sea turtle eggs, after 12–24 hours of incubation, membranes form that attach the embryo to the inner eggshell. Moving eggs after this time risks their survival unless they’re kept upright and in one orientation. With so many laid at once, moving all nests before the time limit ran out was impossible in Mexico, and the unprotected Mexican nests produced fewer hatchlings. In Texas, we continued to relocate all nests, maximizing hatchling production in the state. Shaver hypothesizes that the difference in incubation strategies since 2004 are what led to the difference in numbers of turtles nesting—and hatch success—in both areas.
In 1985, group of government agencies wrote a multi-species plan for all six sea turtle species occurring in the United States. This plan included the first iteration of a recovery strategy for Kemp’s ridley sea turtles. It stated that the primary goal was to restore the population to a level comparable to what was documented in the 1940s. This would be achieved through mitigating terrestrial and marine threats, monitoring the population at nesting beaches and sea, and preventing extinction.
The increasing re-migration interval could partially explain why annual nest tallies are lower and more variable from year to year than what was predicted in the 2011 plan revision.
During the 2011 bi-national revision of the Kemp’s ridley recovery plan, scientists predicted that the exponential increase in nesting observed from 2005 to 2009 would continue. They thought the species could be downlisted to threatened status by 2020. Unfortunately, data collected by park biologists since 2009 showed that the exponential increase in nesting remained elusive. The average re-migration interval—the time it takes for nesting turtles to return—for the Kemp’s ridleys nesting in Texas increased from 2 to 3.5 years from 2015 to 2018. One to 3 years is considered typical for this species, but Shaver’s unpublished data show the interval has been variable since 2018 and reached 3.7 years in 2022. This was the longest re-migration interval documented to date.
The increasing re-migration interval could partially explain why annual nest tallies are lower and more variable from year to year than what was predicted in the 2011 plan revision. Annual nest tallies have fluctuated since 2014, with record-breaking numbers one year and low numbers the next. Biologists in Mexico and Texas are left wondering what the future will bring, as not having a consistent re-migration interval for the species prevents accurate predictions. According to the recovery plan, downlisting this species will not be possible until nesting increases. That seems a long way off at this juncture. But we remain hopeful that our continuing work to protect Kemp’s ridley turtles at the national seashore will get them back on track to recovery.
About the author
Hilary Frandsen is a biologist at Padre Island National Seashore. Image credit: NPS