Sea turtles spread their eggs out for reproductive success

In a new study from the University of South Florida, Professor Deby Cassill reports that loggerhead sea turtles lay their eggs in more than one place to increase the likelihood that some of their young will survive. 

The investigation revealed that some females lay as many as six clutches up to six miles apart during the same breeding season.

“Nesting females don’t lay all their eggs in one basket. Their reproductive strategy is like investing in a mutual fund. Females divide their resources among many stocks rather than investing everything in a single stock,” said Professor Cassill.

“Because females diversify reproduction in unpredictable patterns over time and space, nearly two-thirds of loggerhead sea turtle hatchlings made it into the Gulf of Mexico.”

Over the course of a lifetime, one female loggerhead will lay around 4,200 eggs at 40 different sites. This strategy helps to improve the chances of reproductive success despite various threats such as storms.

“Predation and storms are the primary sources of offspring mortality for eggs and hatchlings on the beach. Once hatchlings enter the oceanic environment, the risk of predation is again high.”

Professor Cassill analyzed 17 years of data from the Conservancy of Southwest Florida on loggerhead females nesting on Keewaydin Island off the southwestern Gulf coast of Florida. Individuals in this nesting population had been tagged and monitored for years. 

The analysis showed that most sea turtle hatchlings reach the Gulf of Mexico, but this rate of success may drop in the future as a result of human disturbances and climate change. For example, strong storms or sea level rise could flood or wash away the clutches.

“It’s important to follow individuals over time to really get a glimpse of how they mate, find food and ensure that some of their young survive to maturity. Without knowledge of the sea turtle’s survival and reproductive biology, we cannot develop and implement effective conservation policies,” said Cassill.

The research is part of a series of upcoming studies conducted by Cassill to support her “maternal risk management model,” which looks at how natural selection pressures, such as predators or a lack of resources, influence how mothers invest in offspring quantity and quality.

Cassill proposed the idea that turtles and fish invest in large numbers of offspring when the threat of predators is high. Mammals, like whales and elephants, provide extensive care to one offspring at a time when there is a seasonal drought or food shortage. 

“Without knowledge of the sea turtle’s survival and reproductive biology, we cannot develop and implement effective conservation policies,” wrote Cassill.

Without the implementation of well-informed conservation policies, sea turtles are likely to join the ichthyosaurs and plesiosaurs as a note in the annals of extinct marine reptiles.

The study is published in the journal Scientific Reports.

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By Chrissy Sexton, Earth.com Staff Writer