New research from the University of Alabama at Birmingham suggests that Kemp's ridley sea turtles, the world's most endangered sea turtle species, is in even more trouble than previously thought.
These sea turtles, found primarily in the Gulf of Mexico, are listed as critically endangered on the International Union for Conservation of Nature's (IUCN) Red List of Threatened Species. Researchers tasked with identifying the species' level of endangerment found that the animals' recovery has stalled at less than one-tenth of historic nesting levels.
After being brought to the brink of extinction in the 1980s, conservationists were able to slow their decline and even saw an exponential recovery rate in 2009. However, this comeback streak did not last as long as hoped when researchers reported a significant drop is nestings in 2010.
To figure out how many Kemp's ridley sea turtles constitute a viable, healthy population, researchers turned to a historic film recorded in 1947 by Andres Herrera, a Mexican sportsman, on the Kemp's ridley's primary nesting beach in the western Gulf of Mexico.
This film captured a mass-nesting event known as an arribada, involving tens of thousands of nesting turtles on a single day in 1947. This event, researchers explained, provided a rare benchmark for evaluating the historic population size of a species prior to its becoming endangered.
"At the time of the film's development, no one was able to connect the dots between the phenomenon of the mass nesting and that the nests belonged to the Kemp's ridley sea turtles," explained Thane Wibbels, a biology professor in the College of Arts and Sciences, who led the study. "Herrera was a hobby enthusiast who wasn't aware of the pursuit in the scientific world to uncover this location. Meanwhile, Archie Carr, who was considered to be the world's leading sea turtles expert, had been searching for the nesting beaches for this species for decades."
With this film, experts estimated that there were more than 40,000 nesting Kemp's ridley sea turtles on the beach that season. The latest study, however, counted about 26,000 sea turtles on a 1- to 2-mile stretch of beach on the day the film was taken. And, over the course of the entire 1947 nesting season, researchers estimate between 120,000 to 180,000 nests were laid. This is a remarkable amount, compared to the 14,000 that were laid in the most recent nesting season.
"Because the Kemp's ridley is so protected, scientists believe that potential factors limiting its recovery may be habitat-related," said Elizabeth Bevan, a doctoral student at the University of Alabama at Birmingham. "Another hypothesis among the field is that environmental pollution, in particular the 2010 Deepwater Horizon oil spill, may have significantly impacted the population, and many years may be required before the species regains an exponential recovery rate."
Researchers also note that the abundance of blue crabs - a preferred food item for the Kemp's ridley - has significantly declined in the northern Gulf of Mexico in recent decades. This indicates the Gulf may not be able to support the abundance of Kemp's ridleys it once could.
"Solving the mystery will require continued monitoring of turtles on the nesting beach, a better understanding of the ecology of the Kemp's ridley in its foraging and developmental habitats, and an evaluation of potential changes in the Gulf of Mexico ecosystem since the 1947 Herrera film," Wibbels concluded.
Their findings were recently published in the journal Ecosphere.
