Green turtles mate in the surf off Gulfstream Park.
Photo provided by Joan Lorne
By Cheryl Blackerby
Halfway into sea turtle nesting season, the research is coming in, and the numbers are both surprisingly good and unexpectedly grim.
Green turtles are nesting in record high numbers. But many turtle hatchlings are being lost to disorientation from “urban glow.” Even on dark beaches, hatchlings are walking toward the western glow of cities, not east toward a star-lit ocean.
“We just broke a record for green turtles. The old record was 154 nests in Boca, and as of today it’s 155 and it’s only July,” said Kirt Rusenko, marine conservationist at Gumbo Limbo Nature Center, on July 17.
Loggerhead turtle numbers were also up in Boca Raton. “Last year there were close to 1,000 nests, and so far this year there are 994,” he said.
Countywide, leatherback and loggerhead nesting is a little less than last year, but turtle experts were anticipating the lower numbers.
“We were expecting less because last year was a record-breaking year. It’s a pretty much average season for leatherbacks and loggerheads,” said Paul Davis, division director for the Palm Beach County Department of Environmental Resources Management.
But green turtles are another, much more exciting, story.
“We’re getting reports of three times as many nests as last year, which will put us on pace to likely break a record by the time we’re done. The green turtle nesting numbers are surprising, shocking — whatever superlatives you want to throw in,” Davis said.
But there’s bad news, too, that also has taken scientists by surprise: Hatchlings are dying from disorientation caused by urban glow or “sky glow,” the light projected into the sky by cities at night, creating an illuminated horizon that causes hatchlings to walk toward the west instead of the ocean.
“In the last nest, we had 100 eggs, and 60 hatchlings scattered in all directions and probably didn’t make it into the water. Overall, we’re probably losing 30 percent of hatchlings to disorientation caused by sky glow,” said Rusenko.
He tracks sky glow with a computerized monitor that records the light every 15 minutes. In recent weeks, low clouds have amplified the light from urban areas, making a powerful amber glow than can be seen for miles and lights up the night sky.
“We’ve had pretty bad disorientation in Spanish River Park beach, and that beach has no lights,” Rusenko said. Even with the lights turned out on the beach, the glow from the city on the west side of the Intracoastal Waterway is strong enough to confuse turtles.
“Sky glow is the primary concern for turtle disorientation in the county,” said Davis. “Sky glow is the result of light being reflected off clouds or haze in the atmosphere as we increase the amount of light. Much of city lighting is inefficient, and is being aimed skyward, not doing any of us any good. Our goal is to decrease unnecessary light that’s being lost upward.”
It’s time to turn down the lights in the county’s coastal cities, he said, because the health and safety of the county’s nesting sea turtles are crucial to the rest of the state.
“When you add up all three turtle species, Palm Beach County has the highest number of nests per mile in the continental United States. What we do here in the county affects almost 25 percent of the nesting in the state, and has a direct affect on the success of sea turtle conservation in Florida.”
There are no real numbers on hatchling disorientation countywide, said Davis. “We have not gotten very many reports of disorientation. We speculate this has been a rainy season, and it’s harder for people to see hatchling crawls. It’s hard to see if they went in the right direction.”
Turning out the lights on the beaches may have been a reason for the comeback of green turtles, whose numbers dropped 50 percent from 1999 to 2009 and prompted scientists to consider changing the turtles’ designation from threatened to endangered.
“The green turtles started shooting back up to numbers we haven’t seen in the last 20 years. It could be that the turtles naturally have cycles like that — we’ve only been recording nesting since the 1970s,” said Rusenko. “But lighting ordinances began in the 1980s, so we may be seeing benefits of the conservation efforts including turning off lighting on beaches.”
Cities are becoming more aware of light pollution. Boca Raton installed full cut-off lighting — lighting that shines fully on the ground — at City Hall, the new library, and the city police building.
Individuals also can reduce urban glow. Davis and Rusenko offer these tips:
• Use full cut-off lighting fixtures that project light on the ground and not into the sky. “These lights actually put more light down where you need it,” said Davis.
• At Lowe’s and Home Depot, look for Dark-Sky approved light fixtures.
• Use amber lights.
Stay informed about light pollution by attending International Dark-Sky Association (idapalmbeach.org) meetings held at 5:30 p.m. the first Friday of every month at the Florida Atlantic University observatory. The group has helped high-rise condos change their lighting and is involved in other projects such as retrofitting lighting in state parks and educating the public about light pollution and its effect on the health of people and wildlife.
Rusenko is a founding member, and he and Davis are board members.
Comments