All the Single Ladies

ENVIRONMENT

At the Pacific Ocean’s largest green sea turtle rookery, a crisis is unfolding—up to 99% of the turtles are female. (National Geographic)

Download and print your own coloring page of a sea turtle.

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit.

This beautiful Australian green sea turtle was photographed in 1972, making it more likely to be a male than turtles in the current generation.
Photograph by Bates Littlehales, National Geographic

Discussion Ideas

 

  • The great Nat Geo article begins “The turtle wranglers landed on Ingram Island thinking about sex and heat.” Why were they thinking about sex and heat?
    • Scientists were collecting data on the possible impact of climate change on the sex of green sea turtles in the northern Great Barrier Reef. To do this, they were counting and comparing the numbers of female and male turtles in the region.
      • Since the sex of a sea turtle is determined by the heat of sand incubating their eggs, scientists had suspected they might see slightly more females. Climate change, after all, has driven air and sea temperatures higher, which, in these creatures, favors female offspring.”
      • Since turtles return to the vicinity of the beach on which they hatched to breed, tracking turtles on islands in the northern Great Barrier Reef allowed scientists to track a large, specific population over decades. (This is great for research.)

 

  • How do scientists determine the sex of sea turtles? (No, looking at their underbellies won’t help.)
    • physical characteristics. As adults, males are generally bigger, and have longer tails and larger claws on their front flippers. This is not always a reliable indicator of sex, and hatchlings all look the same.
    • DNA. Scientists used an innovative new technique to decipher the sex of marine species based on hormone levels found in the animal’s blood. So turtle wranglers “stood atop skiffs and raced toward swimming turtles and launched themselves like bull wrestlers onto the animals’ carapaces. After gently steering each turtle to shore, they took DNA and blood samples, and made tiny incisions to inspect turtle gonads.”

 

  • What were the results?
    • Females outnumbered males by at least 116 to one. The disparity was more pronounced among younger generations.
      • 86.8% of adult-sized turtles
      • 99.8% of subadult turtles
      • 99.1% of juvenile turtles
    • One site, Raine Island, has been producing almost exclusively female turtles for at least 20 years.

 

  • Were any other green sea turtle populations studied?
    • Yes. In addition to rookeries in the northern Great Barrier Reef, scientists studied “turtles hatching from the southern reef near Brisbane—where temperatures have not increased as significantly … There, female turtles today outnumber males by only 2 to 1.”
      • “This combined with some neat modeling shows that cooler beaches in the south are still producing males, but that in the more tropical north, it’s almost entirely females hatching,” says one sea turtle expert. “These findings clearly point to the fact that climate change is changing many aspects of wildlife biology.”

 

  • What does the feminization of green sea turtles in the northern Great Barrier Reef mean for the future of the species?
    • Ultimately “it is unknown how many (or what minimum proportion of) males is sufficient to sustain sea turtle populations.” This sufficient number is called a stable operational sex ratio (OSR).

 

TEACHERS TOOLKIT

Nat Geo: 99% of These Sea Turtles Are Turning Female—Here’s Why

Nat Geo: Sea Turtle coloring page

NOAA: What causes a sea turtle to be born male or female?

(extra credit, great read!) Current Biology: Environmental Warming and Feminization of One of the Largest Sea Turtle Populations in the World

One response to “All the Single Ladies

  1. Pingback: All the Single Ladies — Nat Geo Education Blog Re Green Sea Turtles! | huggers.ca·

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