Astounding: 1947 Video of 26,000 Sea Turtles Nesting vs. Decline Since BP Oil Spill
Astounding video of 26,000 sea turtles nesting highlights losses since BP oil spill, say UAB scientists
The world’s most endangered sea turtle, the Kemp’s Ridley, suffered a 34 percent decline in the number of nests laid in 2015 compared to the year before the BP oil spill, according to a new study authored by scientists at the University of Alabama at Birmingham.
The study analyzes both the recent decline, seen since 2010, and a stunning and massive 99 percent drop in the overall population between 1947 and 1985. The status of the present population is measured against a historic estimate based on film footage shot on a Mexican beach in 1947.
That footage is simply astounding. In it, tens of thousands of Kemp’s ridley turtles are seen lumbering from the sea en masse to nest in an aggregation called an arribada. The camera pans up and down a beach crowded with turtles that the animals have a difficult time finding an open spot to dig a nest. In some of the shots, the turtles are barely visible due to all the sand being thrown in the air by their digging. The turtles stretch off in the distance, as far as the eye can see.
The grainy footage was shot by Andres Herrera, a Mexican sportsman and naturalist. While it was clear from the film that incredible numbers of turtles were on the beach, the camera work was handheld and shaky, with lots of pans along the horizon, most too quick for accurate counting of turtle numbers.
This nesting event on a Mexican beach in 2015 involved about 7,000 turtles. In the 1940s, tens of thousands of turtles would use the same beach in a single day.
Using modern digital video equipment, the UAB scientists were able to dissect the film in a new way, and create composite images of vast stretches of the beach by combining various shots. From those images, Thane Wibbels and Elizabeth Bevan made estimates for the nesting population.
By their count, about 26,000 turtles were laying eggs on a two-mile stretch of beach on a single day in 1947. Further extrapolation suggests the overall Kemp’s ridley population at the time included 180,000 nesting turtles in 1947. Last year, scientists believe there were about 14,000 Kemp’s ridley nests, Gulfwide.
“I consider it a signature species for the Gulf of Mexico,” said Thane Wibbels, one of the study’s coauthors. “The northern Gulf of Mexico appears to possibly be the most important foraging ground, developmental habitat, and migratory corridor for the Kemp’s ridley. They grow up and live here but head back to the western Gulf to nest for a couple of months every year on a beach near Rancho Nuevo.”
Herrera spent two years searching for the mass turtle nesting site near Rancho Nuevo after hearing about it from locals. Ultimately, he discovered the site after making 33 flights along the coast in his small plane, then returned to film it. His film was first seen by scientists in 1961, a dozen years after it was made. It caused an international sensation among turtle scientists, who had been searching for nesting sites for the species for decades.
“The 2010 Deepwater Horizon oil spill, may have significantly impacted the population,” Elizabeth Bevan, UAB.
The Kemp’s Ridley is easily the most common turtle seen in Alabama waters and along the northern Gulf Coast today, and the same was likely true before the population began to decline. Mobile Bay is considered one of the most important juvenile feeding grounds, and dead turtles turn up with distressing regularity in Alabama. Herrera’s discovery explained why no one had ever been able to find a significant number of Kemp’s Ridley nesting sites along the Gulf Coast or in the Caribbean, despite their ubiquitous presence in nearshore waters each year.
Today, his discovery provides a window into the past that scientists hope will lead to further recovery for the species. The great mystery is what caused the decline seen in recent years.
The overall population was experiencing exponential growth in the years since 1985, Wibbels said, when scientists believe about 750 nests were laid. By 2009, that number had climbed to around 21,000 nests. Scientists expected the recovery to climb steadily. But that hasn’t happened.
Instead, in the years since the spill, nesting has fallen off. Some point to limits on habitat and growing coastal populations.
“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,” said Elizabeth Bevan, working toward her doctorate at UAB. “The Kemp’s ridley could be significantly impacted by long-term changes and the overall health of the Gulf of Mexico ecosystem because of its near exclusivity to the area and presence as a higher-trophic-level predator.”
A decline in prey items, such as blue crabs, may have also played a role.
“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 said. “It’s a local species. The Kemp’s riddle is definitely part of Alabama’s heritage. Probably the most abundant sea turtle in this area until it almost went extinct in the 1980’s. Hopefully it will get back to that status in the future.”
The study was published this week by the Ecological Society of America. You can read it here.