HARLINGEN — The critically endangered Kemp’s ridley sea turtle had an off-season for nesting this year along Texas beaches, with 190 nests recorded in Texas.

The number, which covers a geographic area from the Bolivar Peninsula south to Boca Chica beach, was down from 250 nests logged last year and 353 in 2017.

But this year’s sharp drop-off in Kemp’s ridley nesting in Mexico has set off yellow-flag alerts among scientists who track and study the species.

“Just to try and put things in a little perspective, 99 percent of the world population nests in Mexico,” said Pat Burchfield, the executive director of the Gladys Porter Zoo in Brownsville who has served as bi-national coordinator for the joint U.S.-Mexico Kemp’s ridley recovery effort for four decades.

“And we were surprised at the low numbers,” he added. “Basically, it was only about 40 percent of what nested in 2018 and ‘19.”

The vast majority of Kemp’s ridley turtles nest along three main beaches in the Mexican state of Tamaulipas — Rancho Nuevo, Tepehuajes and Barra del Tordo.

Burchfield stressed his nesting number of about 11,000 is unofficial since the Mexican government has yet to issue its final report for 2019.

“This season created more questions than answers,” he said. “Because we’ve anticipated a lot of things that could happen and may happen and we may be seeing, but we don’t have any empirical evidence to nail which things may be going on.”

Texas numbers hold

The Texas nesting numbers, to be clear, were not necessarily poor by the standards of the past decade and they tend to fluctuate because adult females don’t return to their home beach every year to lay a clutch of eggs.

Recent studies show female Kemp’s ridleys may come back to nest at three to three-and-a-half year intervals.

“It is an increase from what we had in previous years and what is possibly the norm for this species,” said Donna Shaver, chief of the Division of Sea Turtle Science and Recovery at Padre Island National Seashore near Corpus Christi.

Yet Shaver voiced her concern about the surprisingly low nesting numbers in Mexico.

“Now why that is, is unknown,” she added. “It probably has to do with food webs and food availability which could be related to changes in crab populations, which could be affected by freshwater in-flow and hypoxic zones and temperatures. It’s complicated, and it takes collaboration among scientists collecting data over a period of years to try to tease out what’s happening.”

Is it the spill?

Nesting numbers on South Padre island and Boca Chica beach show there were 41 nests on South Padre and just six nests on Boca Chica this season, a total which is less than half the nests recorded there in the record year of 2017.

Jeff George, executive director of Sea Turtle Inc. on the Island, said the numbers had begun bouncing back following the 2010 Deepwater Horizon oil spill in the Gulf of Mexico.

“I’m sure that the spill had some impact” on nesting numbers, he said. “Who knows how much or how long it’s going to have an impact? But there is science that says there’s oil in the keratin (shells) on the mommas, so we know they were in the oil. Just, man, I don’t know. I don’t know if anybody’s going to give you a definite answer.”

The impact of the 2010 oil spill is a hugely complicating environmental factor in an already complex ecosystem in which Kemp’s ridley sea turtles operate.

George says nesting increases were “almost linear in the 1990s.”

“And then in the 2000s, by and large, it was exponential,” he said. “Since 2010 it’s kind of been all over the map.”

Drifting at sea

One of the reasons the Kemp’s ridley species is so difficult to study involves the life cycle between hatchling and adult. After emerging from nests along Gulf of Mexico beaches, young Kemp’s ridleys inhabit a different environment than adult turtles.

These tiny turtles spend their juvenile years floating in masses of Sargassum algae in the open ocean, providing resting and feeding spots and giving them cover from predators.

This “drifting” period is believed to last one to two years until the hatchling reaches about 8 inches in length, when it leaves this oceanic phase and migrates to near-shore areas of the gulf to mature more fully. Kemp’s ridleys are not fully mature until they are 10 to 12 years old.

In that Sargassum, researchers found traces of a chemical used to sink the oil, which presumably also washed over juvenile Kemp’s ridleys. It’s another factor for researchers to puzzle out, George said.

Shaver said studies had shown that growth rates for Kemp’s ridley turtles were beginning to decline even before the 2010 oil spill, perhaps the result of a drop in the blue crab population, a species which makes up a large part of the Kemp’s ridley diet.

“So something was going on even before then,” Shaver said. “We’re kind of on a roller coaster with the Kemp’s ridley nesting numbers. When the recovery plan was written right before 2010, before the spill, the population models had predicted continued exponential increases in nesting numbers and that the species could be downlisted to threatened by the year 2020.

“That’s not going to happen,” she added.

Research lagging

Sea turtle researchers seem frustrated by a lack of scientific data on turtles which leads to a great deal of educated theorizing. But Burchfield said cooperation between U.S. and Mexican scientists in the bi-national effort is making the most of the resources available.

“With all that’s happening down there, to me it’s amazing that Mexico has well over 100, and it may be close to 150, sea turtle projects they oversee,” he said. “Sea turtles are totally protected in Mexico at this point in time and that’s kind of amazing. My hat’s off to them.”

But gaps in research seems to strike even harder during years like this one, where nesting numbers were significantly off in Mexico and no one can pinpoint why.

“There’s precious little money for research, and so a lot of these questions that are logical, you’d want to know answers very quickly based on a year like this year,” Burchfield said.

“Maybe next year it will go through the roof, we don’t know,” he added. “Maybe it’s taking them longer to have enough fat to yolk a clutch of eggs to be able to come up to nest. Or there may be some other factor involved entirely.”

Indeed, despite decades of increasingly sophisticated scientific monitoring of sea turtles when funding can be found, much of their lives remain a mystery, wrapped in the enveloping waters of the world’s warmer oceans. This may be, at least in part, one of the reasons for the continuing human fascination with these ancient maritime species.

“It’s not doom-and-gloom,” George said, “but everybody’s scratching their heads saying, ‘Where did they go this year?’”

2019 Kemp’s ridley turtle nest

Total — 190

Padre Island National Seashore — 117

South Padre Island — 41

Boca Chica — 6

2017 Kemp’s ridley turtle nests

Total — 353

Padre Island National Seashore — 219 (area record)

South Padre Island — 70 (area record)

Boca Chica — 23 (area record)

Source: Turtle Island Restoration Network