Cooler Sands of Keewaydin Island Producing the “Cool Guys” of Loggerheads

When Mom sea turtle deposits her eggs on the beach, they are not males or females. According to sea turtle scientists, unlike mammals with an X or Y chromosome, it is the environment of the nest that determines the sex of sea turtles called “temperature-dependent sex determination.”

Research has shown that if turtle eggs incubate below 82.4 degrees Fahrenheit, the hatchlings will most likely be males. If the eggs incubate above 89.6 degrees Fahrenheit, the hatchlings will most likely be females. Incubation temperature below and above 84.2 degrees will produce a nest with a mix of male and female hatchlings. Thus, the phrase “cool dudes, hot chicks.” 

Jill Schmid, a GIS Specialist for Rookery Bay National Estuarine Research Reserve (RBNERR), has been conducting the longest running and most intensive incubation temperature study of sea turtle nests on Keewaydin Island since 2001. Keewaydin Island is located within the Rookery Bay Reserve.

Jill has been collaborating with the Conservancy of Southwest Florida; their sea turtle interns deploy temperature data loggers inside the sea turtle nests which take hourly temperatures. The loggers remain inside the nest until the hatchlings emerge and the nest is excavated and evaluated for hatchling success.

Usually, the eggs are a foot down from the top of the sand and insulated from the daily temperature fluctuation. While the nest is incubating, the metabolic heat that is generated from the eggs will also increase the temperature. According to Jill, the placement of the data loggers deep inside the nest is key. Loggers that are placed closer to the top will record more temperature fluctuations when it cools down at night.

At what point during the incubation period is sex determined? According to Jill, on a 60-to-65-day cycle on Keewaydin Island, sex is determined during the middle third of the incubation period.

Since 2001, Jill has deployed over 1,400 temperature data loggers in sea turtle nests on Keewaydin Island. The data collected shows that Keewaydin Island has been trending towards male hatchlings, which makes it a very important nesting ground and critical to the survival of the loggerhead sea turtles. Keewaydin Island is supplying the Florida loggerhead population with much needed males.

According to Jeanette Wyneken, Biological Science Professor at Florida Atlantic University, the vast majority of sea turtles born on Florida beaches have been females and from their studies, females have been outnumbering males. The warmer sands of the East Coast of Florida have been producing more female sea turtles. The warmer the nest, the faster they will incubate, and nest there typically hatch in 45 to 50 days.  

What will it do to the species if there are more females than males? According to Jill Schmid, since loggerheads are threatened it is actually good that there are more females than males.  The females can lay more nests; they have multiple paternity, and you don’t need a whole lot of males since males can mate with multiple females.  

Jill added that having a clutch that may have three different fathers will keep the genetics moving.  Female sea turtles are not monogamous and as they travel around the world, they can mate many times with different males. It is good for the loggerhead species to have that genetic variability – it keeps the species stronger.

This makes the production of the “cool guys” from Keewaydin Island very important to the loggerhead sea turtle population.

How Jill got started: She started with a biology course in college with an amazing professor.  After graduation, Jill interned at the Conservancy of Southwest Florida with their sea turtle program on Keewaydin Island with Dave Addison.

Jill was hired by Rookery Bay Reserve as part of a large-scale Australian pine removal project on Keewaydin Island. She became interested in how the restoration would impact sea turtle nesting and it became her master’s thesis project. Were the sea turtles able to nest in areas that were previously inaccessible due to fallen pines on the beach? Second part was to evaluate whether removing the standing Australian pines (source of shade) would affect nest incubation temperature, thus altering the sex of hatchlings?

What started out as a short-term master’s research project continued into a project over 20 years long. According to experts, though sea turtles have survived the challenges over eons, the climate is getting hotter faster creating a sex imbalance in sea turtle population. Will sea turtles learn to adapt to save the species? The future of sea turtles is in our hands!