Turtle Traffic Jams?

On Oahu’s North Shore, Hawaiian green sea turtles are everywhere, but a recent study claims that may not be the case in the future due to climate change.

But is it really true that disaster is looming for green sea turtle populations?

Tourists flock here daily to see them, with cars and buses jockeying for limited parking along a tiny, two-lane coastal highway. The daily phenomena create what the locals un-affectionately refer to as “turtle traffic jams.”

When I surf, turtles occasionally surface in my path, and I lean over and glide my hand across their carapace to avoid a collision. On rare occasions, we spot them hopelessly entangled in fishing line. Donning masks, snorkels, and knives, we rush out to cut them free.

The majority of Hawaiian green sea turtles nest each summer at French Frigate Shoals (FFG) in the Northern Hawaiian Islands. Since monitoring of FFG nesting began in the 1970’s, sea turtles have rebounded dramatically. In recent years, more are also nesting successfully right here on Oahu.

 

Global Sea Turtle Success

While the sea turtle increases at FFG are impressive, it’s important to note this series of islets has a total land area of only 61.5 acres. While important in its own tiny way, it would be foolish and unscientific to extrapolate the trends on this speck of land to sea turtle populations worldwide. For that, we turn to a recently published research article titled Global Sea Turtle Conservation Successes. Studying 299 time-series similar to the graph above, the scientists found that, globally, 95 showed significant increases, while only 35 showed significant decreases. A large part of this global conservation success story is because, since the 1970’s, humans have made great efforts to steward local turtle populations. Techniques for collection and incubation of sea turtle eggs have improved. Important nesting areas like FFG are now protected and monitored. Shrimp trawlers in the U.S. and elsewhere now use TEDs (turtle excluder devices) to avoid turtles and other unwanted bycatch.

Climate Change Hype Ignores Global Sea Turtle Success

But a recent Washington Post article warned that new research reveals global warming is turning 99% of baby sea turtles into females (actually, the research was not on babies). Before taking this warning too seriously, it’s important to know the Washington Post is no stranger to unfulfilled global warming doomsday prophecies. This is the same newspaper that quoted Al Gore predicting the earth would be a “total frying pan” by 2016. It’s 2018 now, and while global temperatures are slightly higher now than when Gore made his prediction in 2006, they are nowhere near Gore’s doomsday “frying pan” levels. As Dr. Roy Spencer recently described, if global warming theory matched reality, then daily temperature departure maps should show increases almost everywhere, not just in isolated places like they do now.

But what about the Post’s 99% female sea turtles warning? Well, all species of sea turtles exhibit temperature-dependent sex determination. Female sea turtles dig nests on sandy beaches, and the egg incubation temperature largely determines whether the hatchlings are boys or girls. It is a well-documented scientific fact that warmer temps produce more girls and cooler temps produce more boys. In some species, just 1 or 2 °C is all that separates the clutch from being 100% male or 100% female.

Scientists determine a sea turtle’s sex using a variety of methods. The most well-established method is to simply look at an adult sea turtle’s tail. Adult turtles with longer tails are normally males. The tail ID method doesn’t work on juveniles and sub-adults, so turtle scientists used a new approach involving blood sample analysis and laparoscopy. Although laparoscopy is a surefire method for identifying a turtle’s sex, it involves a surgical procedure that could harm the animal. To avoid laparoscopy, while also collecting more data, scientists created a model comparing blood sample analysis of hormone levels to laparoscopy results. Finding a good correlation, they then used the model to predict the sex of juvenile and sub-adult Great Barrier Reef turtles based only on hormone analysis.

A total of 337 green sea turtles were collected from foraging grounds near the Howick Group of islands at the northern edge of the Great Barrier Reef Marine Park, Queensland, Australia. As a group, 77.3% of juveniles, 75.6% of sub-adults, and 80.8% of adults were identified as females. It wasn’t until the scientists used genetics results in an attempt to separate the turtles into groups that they found 99.1% of juveniles, 99.8% of sub-adults, and 86.8% of adult-sized turtles from the Northern Great Barrier Reef (NGBR) group were female. This group’s natal origin, or birthplace, was Raine Island. Like FFG, Raine Island is another tiny, yet important sea turtle nesting site. Scientists also found that warmer Raine Island nesting site sand temperatures occurred with the juveniles and sub-adults than with the 20+ year-old adults. In other words, when the adults in their study were incubating in their nests 20+ years ago, sand temperatures were cooler. The results appear consistent with normal sea turtle patterns, e.g., the warmer the nesting site, the more females are produced.

The Rest of the Story

While the 99% female numbers for these young Australian sea turtles appear robust, there are other important points to consider:

• Scientists report that, for all sea turtle species, “the primary sex ratios of hatchlings are generally highly female-biased.” Numbers approaching 90% females are not uncommon. As a group, the green sea turtles in the Great Barrier Reef study fall within this range.
• The 99% female results were from sea turtles whose natal origin was Raine Island (a.k.a. Northern Great Barrier Reef group). A mere 11.4° south of the equator, Raine Island is naturally warmer than other nesting locations in the study. Therefore, it is natural to expect more female hatchlings at Raine Island than locations farther south.
• The scientists used a new model for determining a sea turtle’s sex. While their methods appear robust, independent verification of their methods is encouraged.
• Note the group as a whole, when compared to the NGBR turtles, has a slightly lower percent of juvenile and sub-adult females. The 99% females from NGBR are used by both the The Washington Post and the scientists in the study to extrapolate the percent female increase in recent years at tiny Raine Island with global warming theory. However, using their own data in their Figure 2 for all Great Barrier Reef sea turtles collected, it is clear that a smaller percentage of females is present in juvenile and sub-adult populations. In other words, using their own arguments, we can conclude that the higher proportions of males in recent years means a cooling trend, not a warming trend, is occurring in the study area.
• Mating is known to occur at the Howith Group of islands, the location of sea turtle collection for this study. As mentioned already, this group of turtles showed normal sex ratios. Also, because mating between groups likely occurs, using genetic markers to distinguish natal origins may be problematic.

Doing Real Things for Sea Turtles

As I wrote this morning, our cell phones here in Hawaii suddenly blared the following warning: “BALLISTIC MISSILE THREAT INBOUND TO HAWAII. SEEK IMMEDIATE SHELTER. THIS IS NOT A DRILL.” Turns out it was a false alarm, but it got me thinking about other false alarms, like an imminent and worldwide sea turtle population collapse. The truth is God designed sea turtles to adapt. We have much to learn about sea turtles, but we do know they have a long nesting season, lasting several months. Most females dig multiple nests throughout the season, some during warmer temperatures, some during cooler temperatures. Worldwide, sea turtles of all species are on the increase.

So, instead of trying to link everything from big snowstorms and extra female sea turtles to a global warming strawman, it might be good to think of things that really make a difference. Simple things like the 3 R’s of reduce, reuse and recycle. Avoiding or limiting your use of things that cause problems for sea turtles, notably plastic bags and plastic straws. Improving your fishing methods so you don’t leave dozens of yards of fishing line snagged on rocks and reefs that are also sea turtle foraging areas. Or even hands-on work like management of beaches on Raine Island so sea turtles have more opportunities for nesting and survival. These are real actions that produce real results.