SOUTH PADRE ISLAND — Experts on the critically endangered Kemp’s ridley sea turtle say this year won’t match 2017’s record nesting numbers in Texas.
But the second-best year on record since 1980 may be good enough.
As of a recent count, North Padre Island had recorded 141 turtle nests and South Padre Island 64. Last year’s 353 nests were a record for the state, although it doesn’t look like this summer’s totals will match it.
“We have to take the long view on this,” said Dr. Donna Shaver, chief of the Division of Sea Turtle Science and Recovery at Padre Island National Seashore.
“We are excited that this year we’ve had as many as we’ve had and we haven’t slipped down below 200, which we could have.”
An annual survey of Kemp’s ridley nests along the Texas and Mexico gulf coasts that began in 1966 showed the number of nests growing each year. But then, following the Deepwater Horizon oil spill in 2010, the number of turtle nests dropped unexpectedly by more than one-third that year and remained below predicted levels until last year.
Jeff George is executive director of Sea Turtle Inc. on South Padre Island, and like Shaver and all who study the critically endangered Kemp’s ridley, he is keeping close watch on nesting numbers to determine the species’ recovery since the spill.
“In light of the decline after the Deepwater Horizon oil spill, is the population beginning to show signs of recovery again?” he asked. “We had a record year last year and the big question was well, let’s see if we got two years in a row, or if it was just a blip.”
George concludes that while this season in both Texas and along Playa de Rancho Nuevo in Tamaulipas, Mexico, where 27,000 of the turtles nested last year, isn’t record-setting, it might be good enough.
“It’s not a record year, but it is certainly a respectable year,” George said. “It shows the population is showing good signs of beginning to recover.”
Nesting times longer
This year marks the 40th anniversary of bi-national recovery efforts for the Kemp’s ridley between the United States and Mexico, and Shaver said the Division of Sea Turtle Science and Recovery plans a celebration in July.
“This year was a big question mark,” she said. “The numbers are fluctuating up and down and it probably relates to the length in re-migration intervals that we have been documenting the last few years — 3.5 years to return rather than two years.”
Re-migration interval means the time it takes for an individual female Kemp’s ridley to return to the beach where she was born to lay her own eggs. Recent studies show longer periods between nesting events, and since the only way to estimate sea turtle populations is through counting nesting females, it’s a complicating factor for scientists trying to compile an accurate sea turtle census.
What’s causing longer nesting intervals isn’t known exactly, but possibilities focus on a change in the available food biomass for the turtles in the Gulf of Mexico. Some scientists think a decline in the blue crab — a favored food for Kemp’s ridleys — could be linked to the major oil spill of 2010.
Unlike the juvenile green sea turtles found in the Laguna Madre which are herbivores, eating algae and sea grass, Kemp’s ridleys are carnivorous, feeding on shrimp and shrimp bycatch, crabs, jellyfish and other invertebrates.
The spill and the resulting fallout on the food chain in the gulf could have disrupted turtle nesting, causing females to put off mating and nesting for a season or two.
George cites three factors in the ongoing recovery of Kemp’s ridley turtles in the gulf and other sea turtle species elsewhere.
One is that turtle conservation efforts over the past four decades are paying dividends. And two, sea turtle conservation and recovery is becoming a robust global effort.
“The third thing is that the fishing industry has bought into the fact that these are important species for their livelihood in the long run,” George said. “For example, the ridleys are important to the gulf ecosystem, and a healthy gulf ecosystem means there are more brown shrimp out there.”
The gulf diet of Kemp’s ridleys include “organisms that are natural prey (particularly crabs, dominated by the blue crab, C. sapidus), scavenged discarded bycatch from shrimp trawling, or organisms that feed on such bycatch,” notes a recently published study by scientists Shaver, Charles W. Caillouet Jr., Scott W. Raborn, Nathan F. Putman, Benny J. Gallaway and Katherine L. Mansfield.
Gulf shrimpers were mandated to add turtle excluder devices to their nets in the 1980s to keep ensnared turtles from drowning. They also now have equipment and nets which reduce bycatch of unwanted fish and other aquatic species.
By reducing unwanted bycatch, a highly praised conservation measure, shrimpers trawling in the gulf may have reduced a valuable buffet line of easy food that Kemp’s ridley sea turtles have learned to exploit.
Which raises the question of just how many Kemp’s ridley sea turtles can the gulf support?
How many are too many?
Low Kemp’s ridley nesting numbers from the oil spill year of 2010 to last year may be at least partially attributable to a declining “carrying capacity” for the species in the gulf.
That means the Kemp’s ridley could reach “peak turtle,” and despite being an endangered species with a vast Gulf of Mexico in which to swim, its particular habitat and food needs could put an upper limit on the species’ total number.
“Some people do ask, ‘well, when are we going to get to the point there’s just no room for anybody else?’” Shaver said. “And that, hypothetically, is something to be concerned about.”
“Some have hypothesized that the carrying capacity has been reduced,” she added.
“We don’t know,” she added. “And that’s another reason to study them over the long term, to try to gather information to understand that to see if perhaps that is a factor.”
Longer timeline needed
George acknowledges there are many questions and even mysteries surrounding sea turtles for which researchers have no answers.
How long do Kemp’s ridley turtles live? How many of them are out there?
“You have to remember we are only in the infancy of sea turtle conservation,” he said. “Rehabbing a few hundred turtles a year is a small benefit to the species, and releasing 10,000 babies a year is a small benefit to the species.
“Our niche, if you will, is public stewardship, getting these kids in the Rio Grande Valley involved, getting our tourists involved, one little change in their life at a time,” George said. “And that’s what I think Sea Turtle Inc. has done very well over the last 40 years.”