When baby sea turtles hatch on a beach at night, their instinct is to head to the sea. The beach slopes down, which is one directional clue they follow. Another is light: The horizon over the sea is brighter than the horizon over land.
But lights from towns and beach developments can distract the hatchlings. The sky glowing above a city can be disorienting, leading them to wander. And particularly bright lights can draw them away from the sea.
You’d think the extra time crawling might wear out hatchlings, which need energy once they get in the water to swim for about a day to get to their destination, the warm current of the Gulf Stream. In a normal sprint from nest to waves, the babies have been shown to build up chemicals that indicate they’ve been pushing themselves.
Sarah Milton, an associate professor of biology at Florida Atlantic University, and Karen Pankaew, a graduate student in biology, collected 150 loggerhead and green turtle hatchlings as they came out of the nests on beaches in Boca Raton, Florida.
The researchers took the hatchlings to a lab, where they ran on a little treadmill and swam in a tank while their blood and breathing were monitored.
The surprise finding: As the researchers reported in the Journal of Experimental Biology, even after a couple of hours scrabbling the equivalent of about 500 yards, the turtles were fine by all measures and swam as well as turtles that didn’t have an extended crawling period.
The reason, apparently, is that they pause frequently in crawling if they are doing it for a long time, unlike the uninterrupted sprint they make when headed straight to the water.
So disoriented turtles are not worn out.
Milton answered questions in a telephone interview about the research.
Our interview, below, has been edited for clarity and length.
Q: This required a lot of late night work. Is that all on the part of your graduate students?
A: I’m always up for the first few nights because I have to train the graduate students. After that it was all on them, and they had a few volunteer undergraduate students to help as well. We actually had planned to have the turtles do an entire kilometer, but it just took so long. It turned out that the turtle could go that distance, but the graduate student couldn’t hang in there that long.
Q: The turtles are snatched up right away and go to the lab where they’re on a treadmill. Do they get a rest before you release them?
A: They were held at a nearby nature center that we work with. They take them out, along with other hatchlings that have been misoriented that people bring to the nature center. Actually, they get a ride out on a boat when some of the local dive masters volunteer, and they take them out all at once and basically drop them off in the Gulf Stream.
Q: What do the hatchlings do when they get to the Gulf Stream?
A: They settle into the weed lines, that’s what they’re aiming for. They can eat all the amphipods and things that are hanging out in the sargassum, and they just live there for the next several years.
Q: Do your results mean we don’t have to worry about human lights?
A: They end up spending a lot longer on the beach than they otherwise would, both because they’re disoriented and because they’re stopping all the time. That makes them very vulnerable to predators.
There’s a lot of things out on the beach that like to eat baby sea turtles. Night birds, raccoons, foxes. And then also, they can end up being still on the beach in the morning when the sun comes up, which means they pretty much would just overheat and die.
There are some people who don’t think that turning off the lights, really, is going to do any good. But I can say from being out on the beach doing the study, it’s very clear that we would have one house that had a porch light on in the back or something like that, and the turtle would head straight for it.
It made me want to leave a note on their door: “Hi, you are personally responsible for the disorientation of 60 turtles last night.” So turning off the lights in the condominiums and in the houses really does make a difference.
The sky glow, though, is different. There’s not as much we can do about that, except basically at a societal level, just because there’s all the streetlights and it casts a glow in the sky. Anyone who lives in a big city can see that.