PBS高端访谈:气候变化正在减少雄性海龟的数量

 　　GWEN IFILL: Now we turn to another angle of our continuing of climate change and its impact.

　　Tonight, our science team looks at the toll 1 it is taking on sea turtles and some of their tiniest offspring. We went to the coast of Southern Florida and came back with a major report that we are launching on our Web site tonight. Here's a part of it.
　　JEANETTE WYNEKEN, Florida Atlantic University: Turtles go back around 230 million years. Sea turtles go back around 110 million years.
　　And while I'm happy to report that we have had a really big nesting year this year and last year, the numbers are still depleted 2 from what they have been historically. So we're not looking at a species that is out of the woods yet.
　　When we think about the biology of the animal, the loggerhead has been around for around 60 million years. There have been a lot of climatic changes during that time, and very few of them have occurred at this rate.
　　It changes where the droughts occur. It changes where the heavy rainfall events occur. It changes where major tropical storms occur and the sizes of the tropical storms. The shift in climate is shifting turtles as well.
　　Now, one of the things that we discovered from those major rainfall amounts or major storm surge events, that we can see the changing in the temperature of the nest. So the reason why the temperature matters is because sea turtles have environmentally determined 3 sex. They don't have an X or Y chromosome 4. They have a sex that's defined during development by the incubation environment.
　　And In general, we have higher biased 6 sex ratios, where female bias 5 is common. If the sand absorbs more heat, we're going to push that female bias, which we know is really common down here, to an even more extreme situation.
　　So, a typical loggerhead down here in Southern Florida is producing about 105 eggs. If a female nests five times, five times 105, if my math is good today, should be 525 eggs. So she will have to nest over 10 nesting seasons, which is about a — in the case of a loggerhead, a 20- or 30-year period, just to replace herself and maybe one mate.
　　If you do a back-of-the-envelope calculation, we're looking at about one in 7,000 making it to adulthood 7. Let's take that same turtle and her nesting over 20 years, so that's 10 nesting events. If five of those, everything gets wiped out by storms, and five of those are drought years where turtle production is low, and it's so hot that everything that comes out of the nest is a female, wow, as long as they can find a date, they have got a future.
　　But if there aren't enough males out there, then — then there is a problem. They have been through some climate changes, but we hope this climate-changing event is not one that they can't recover from, that they can't compensate 8 for. And if it is so bad that they can't compensate, that's a pretty dire 9 statement, not only for the turtles, but for us.
　　GWEN IFILL: I'm joined now by science producer Nsikan Akpan.
　　So, Nsikan, you're a science guy, so you know about melting glaciers 10 and polar bears. Tell us why we care about loggerhead turtles.
　　NSIKAN AKPAN: So, we're calling the series the Wild Side of Sea Level Rise, because we're looking at the infinite little ways that sea level rise will impact wildlife along the coasts.
　　Now, if you look at adult sea turtles, they are not that small, right? They are not that tiny. We know a leatherback can weigh as much as a motorcycle.
　　GWEN IFILL: Huh.
　　NSIKAN AKPAN: But sea level rise is going to have a huge impact on their very small nestlings.
　　So, as Janet mentioned in the — or Jeanette mentioned in the video, sea level rise is washing out nests at a higher frequency than we have seen in the past. Storm surges are a part of that. And then we also have this issue with beach erosion, which is squeezing the amount of area that sea turtles have to nest.
　　GWEN IFILL: Now, I highly recommend people going and reading your report, which is very interesting.
　　But one of the things that struck me was, you found that — you reported that only one in 7,000 of these loggerheads, once they're born, actually make it to adulthood.
　　NSIKAN AKPAN: Right.
　　So, sea turtles, and especially their hatchlings, often serve as prey 11 for a lot of predators 12. So, while we were out there on the beach, producer Mike Fritz and I, we saw a fox running around the beach. And one of the researchers told us that a fox could eat an entire nest of sea turtle eggs, so it could eat 100 eggs in a single sitting.
　　Once the hatchlings make it off the beach and into water, they're often prey for sharks. And so then, when you compound the fact that so few survive natural predation with the fact that beach erosion — or beach erosion and also storm surges washing out more nests, you are going to have sea turtles sort of pushed to the brink 13 in terms of their genetic 14 diversity and also just their population numbers overall.
　　GWEN IFILL: Predators have always been thus, right?
　　But what's different now, it seems that we're talking about the effects of drought and, as you mentioned, erosion and warming and storm surges. Of all of those factors, what would you say is the most dead — having the most deadly impact?
　　NSIKAN AKPAN: Well, I think all of those are having pretty cataclysmic effects.
　　As Jeanette mentioned in the — with her research, they're seeing that drought is forcing the sex ratio bias, where they are going to have almost primarily females being reproduced. And if you have that occur for multiple generations, you can lose a lot of diversity of sea turtles, but also just their ability to reproduce overall.
　　GWEN IFILL: So, what is the solution — or are there solutions, first of all, and are they — there solutions we can pay for?
　　NSIKAN AKPAN: One solution is beach renourishment, which is when you ship sand from offshore 15 and you just try to physically 16 rebuild the beach.
　　For a couple of different reasons, that isn't always the great for sea turtles. Sea turtles have a harder time digging into a renourished beach. Their nests are often misshapen, which can prevent hatchlings from being able to escape. And you just end up with a big trap.
　　GWEN IFILL: And it's an expensive prospect 17, also.
　　NSIKAN AKPAN: It's also very expensive.
　　So, since 1991, Florida has spent over $2 billion to renourish beaches. And if you think about it — if you think about this prospect long term, it isn't very sustainable, because sea levels are predicted to rise by at least five feet by 2100, which — so, beach renourishment isn't really a solution in that case, right?
　　GWEN IFILL: Right.
　　Well, Nsikan, you introduced me to something I knew nothing about and now I find terribly interesting. So, thank you very much.
　　NSIKAN AKPAN: Thank you, Gwen.