Baby sea turtles look incredibly cute as they run on a tiny treadmill and swim laps in a mini-pool, as in the video below, but the reason that physiologist Sarah L. Milton created this elaborate setup is sobering.
Normally, green and loggerhead turtles hatch on Florida beaches at night and instinctively scramble in a frenzy to the ocean, where they swim miles out into the Gulf Stream. But onshore light pollution can disorient the newborn turtles, making them vulnerable to predators and other risks as they struggle to reach the sea. Milton and graduate student Karen Pankaew, both at Florida Atlantic University, set out to measure how exhausted the hatchlings become when they get lost. They put 150 just-hatched turtles on homemade treadmills for jogs of 200m and 500m (220 and 550 yards) and later measured their swimming endurance (after the tests, they took them straight to the ocean).
The study, funded by the National Save the Sea Turtle Foundation and local conservation nonprofit Friends of Gumbo Limbo, could inform efforts to enforce light ordinances that protect these species, which are already threatened by a litany of human disturbances. Oceans Deeply spoke with Milton about her research, which was published recently in the Journal of Experimental Biology.
Oceans Deeply: Why did you and your coauthor decide to put baby sea turtles on treadmills?
Sarah L. Milton: When the sea turtles get disoriented, they can crawl for as much as a mile on the beach, when it should be a matter of maybe only 100 yards (91m) or less to get to the water. The question is: If they crawl that far, do they actually still have any energy to swim? How much energy are they using when they’re crawling for these very long distances?
When the turtles get to the water, they swim for 24 hours straight to get basically out to the Gulf Stream. If they don’t have the energy to swim for that 24 hours, they may not actually make it. One way to measure how much energy the turtle is using is looking at oxygen consumption. When you are sprinting versus going for a stroll, you’re using a lot more oxygen; so does a baby sea turtle.
With a human, what you would do is put a mask on them and measure the amount of oxygen they inhale and exhale. But you can’t really put a mask on a baby sea turtle and still have them crawl. The only way to do it was to put them in, essentially, a box, where we could measure the oxygen levels in the box and then put the treadmill in the box to make them crawl.
Oceans Deeply: That’s very creative. Did you have to build the treadmills yourself?
Milton: Actually, it’s a modified belt sander. We put on a power coupling so that we could reduce the speed. That powered it down so it moves very slowly.
Oceans Deeply: How did you do the experiments?
Milton: We worked with a city park and nature center that patrols the beaches. They record when all of the nests are laid, and then we can tell about when they are going to hatch, within a couple of days. My graduate student would wait on the beach every night, get the turtles that hatched and then bring them back to the lab and do the experiments that night.
The experiments take a long time. It can take as long as seven hours for the turtles to crawl the 500m, because they keep stopping to rest. We did it over the course of the entire summer. The next summer, we did the field work to compare it to the lab results.
Oceans Deeply: How did you measure their swimming ability after they did the treadmill workout?
Milton: After the turtles walked either 200m or 500m, we would put them in an enclosed box with the turtles in a little bathing suit that is tethered to the roof, so they don’t crash into the walls as they swim. Then, they just swim and swim and swim. They are basically just swimming on a string. Since that was an enclosed box, we could also measure the oxygen consumption. We could look through the top of the box and see how often they breathed and how fast they were paddling their flippers, so we could measure their swimming endurance as well.
Oceans Deeply: I read you were surprised by the results. What were they and why were you surprised?
Milton: People have done physiology studies on turtles just as they are digging out of the nests and then running on the beach and out into the water. If you look at just those animals, the energy they expend is very high. They produce a lot of lactate, which is the same thing we produce if you go running really hard. It makes you sore the next day. They use a lot of oxygen.
If you just took how much energy they used in that short run and multiplied it by, say, five hours, the [experimental turtles] should be completely exhausted. But we were surprised. It turns out that if you have them going for that long a time, they don’t run continuously. Instead, they crawl for a couple of minutes and they stop and rest for a couple of minutes. Every time they rest, that allows them to burn up some of that lactate and they don’t get as tired. They never got as tired as we thought they would, and they could swim just fine once we put them in the swim chamber.
It shouldn’t really be a surprise. No one can sprint for hours and hours.
Oceans Deeply: So the hatchlings don’t get too tired to swim. Is it still a problem, then, that they get disoriented on the beach?
Milton: Yes, they are spending much, much longer on the beach. It’s not a matter of just walking in the wrong direction. They are walking in the wrong direction for a very long time and getting tired. As they get tired and keep stopping to rest, they are spending even more time on the beach.
There’s a lot of predators on the beach. The longer [the turtles] are on the beach, the more likely they are to get eaten or still be there in the morning when the sun comes up, and then they are just going to overheat and bake, basically.
Also, when hatchlings come out of the nest, they hatch all at once. It looks like a little volcano – it’s adorable. They all run down to the water at the same time, so it’s hard for a predator to pick off any one of them. But if you are just the lone turtle wandering around the beach, it’s very easy for a predator to find you.
Oceans Deeply: Are many sea turtles dying on Florida beaches because of light pollution?
Milton: Yes, quite a few. It’s been improving lately because some cities are making a strong effort to reduce light pollution, but in a lot of urban areas there is still light pollution that distracts them. On our beach in Boca Raton, as many as 50 percent of the turtles can be disoriented. A lot of them will eventually make it to the water, but not all of them are going to.
Oceans Deeply: Are there measures of their survival rate?
Milton: One of my colleagues is doing a study, and that should be published relatively soon. They actually had camera traps out so they could see what was eating the hatchlings. They were comparing different parts of the beach, like an urban area versus a park.
Oceans Deeply: Is light pollution the main threat that sea turtles face?
Milton: There are many threats. It certainly is one of them. There are areas where [people] still harvest eggs and they still harvest sea turtles, even though they aren’t supposed to. There’s a lot that get caught in fishing nets. They eat plastic. Climate change is a big threat. Storms wash out the beaches. There’s a risk of feminizing the turtles because of temperature change. But light pollution is certainly one of the biggest ones for hatchlings.
Oceans Deeply: Do you think city or state governments can or should do more to protect hatchlings?
Milton: Most cities actually have light ordinances, where you are supposed to not be shining lights on the beach during the sea turtle nesting season. Not all cities enforce those; obviously, it costs money. There’s a lot of places making progress, and encouraging people to switch to turtle-safe lighting is fairly straightforward.
Part of the problem is that even if you do that right along the beach, there’s still just a lot of sky glow from the city. That causes disorientation as well. The turtles just don’t know where they are going then. They may just wander around, and that’s a lot harder to address.