As global air and sea temperatures rise, numerous species are facing the consequences of our actions. Habitats are disappearing, climate change is shifting habitable zones, and some animals just can’t take the heat. Among the sea turtle populations, scientists are observing an unusual and disturbing trend that could prove fatal in a matter of generations.

A Biology Lesson

Sea turtles are part of a group of reptiles whose biological sexes are determined by their environment. Specifically, sea turtle eggs are impacted by the temperature of the sand around them. If the sand is cool, the eggs hatch as males. If the sand is warm, the eggs hatch as females. Rising temperatures had scientists wondering if more heated sands might mean that slightly more females were hatching. To find out, they traveled to a major sea turtle breeding ground near the Australian coast.

When they arrived, the marine biologists set out to determine the sexes of the sea turtles that had returned to their breeding grounds to lay eggs. Blood tests and laparoscopic observations helped the scientists count and catalog the number of females and males present on the breeding grounds. Their findings were undoubtedly fascinating, confirming their suspicions, but more than that, they also established the scientists’ greatest fears. Not only had the number of female turtles risen with the increase in temperature, but the males had become outnumbered 116 to 1.

The Undeniable Truth

Raine Island, one of the major breeding beaches in the Coral Sea area, is a point of significant concern for scientists. The rookery is nesting grounds for up to 200,000 turtles, with 18,000 coming to nest at any given time during peak season. With such a high output, maintaining gender diversity is important, which is why what the scientists found was so alarming. Based on their analysis, Raine Island has been producing almost exclusively female offspring for nearly 20 years. The ratio of females to males has been increasing since the 1970s and 80s, though the numbers were closer to 6 to 1 back then.

As the sea temperatures rise, the coral bleaches and the sand grows ever warmer, scientists worry that the outlook may be grim for these massive turtles. But, all is not lost. At another breeding ground near Brisbane, farther south where the temperatures are cooler, the female turtles only outnumber the males by a factor of two-to-one. The difference between the two rookeries confirmed for the scientists that climate change was playing a significant role in the female-favoring shift.

A Worldwide Perspective

Studies of breeding grounds across the world indicate that the global average is shifting noticeably in favor of females, with a roughly 3 to 1 average ratio. Having the numbers slightly skewed toward females might not be all bad, as long as the bias remains relatively small. Male turtles can mate with multiple females, which continues to work out just fine when there are a few more ladies around than there are gents. However, as the temperatures climb, scientists fear that the variation might become more noticeable as it has on Raine Island.

Although sea turtles have been around for thousands of years, the temperature fluctuations in the past have been gradual. Present-day turtles are seeing climate swings throughout single-lifetimes as opposed to generations. The oceans 50 years ago were cooler and cleaner than they are today. In coming decades, we may witness the extinction of some endangered species of turtles as their breeding grounds warm and skew their gender ratios. With any luck, the turtles will migrate to cooler waters and save themselves.

Other than these all-female turtle births, there have been a lot of other really strange things happening in our oceans lately…