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More Loggerhead Nests, Encounters on Sanibel in Recent Years

October 11, 2023
loggerhead sea turtle nesting at night

Compared to the 1970s and 80s, Sanibel is now averaging approximately 5 times more loggerhead nests and 6 times more loggerhead turtles encountered on night surveys each year, according to a recent analysis from the SCCF sea turtle team.

With sea turtle nesting season nearing completion, the SCCF sea turtle team has stayed busy proofing and analyzing data. One of their latest projects involved comparing various reproductive metrics from our historical and current datasets to see if and how loggerhead nesting behavior and reproductive success has changed over the decades.

They analyzed historical data from the very first years of nest monitoring on Sanibel (1959 – 1989) and compared those metrics to more recent data (2016 – 2023), finding that we are seeing many more loggerhead nests and nighttime encounters than before.

“These trends could be a result of successful initial conservation efforts,” said SCCF Sea Turtle Biologist Savannah Weber.

man measuring loggerhead sea turtle on sanibel
Sea Turtle Researcher Charles LeBuff measuring a loggerhead on Sanibel in 1973.

History of Sea Turtle Monitoring on Sanibel

Sea turtle monitoring on Sanibel was first led by sea turtle researcher Charles LeBuff and Caretta Research, Inc. until it was transferred to SCCF in 1992.

It’s one of the longest-running monitoring programs in the country and operates under a permit granted by the Florida Fish and Wildlife Conservation Commission.

“It’s possible that hatchlings that Charles LeBuff and Caretta Research, Inc. helped protect back in those early years of sea turtle monitoring have survived to adulthood and are now turtles we’re encountering nesting on Sanibel!” Weber said.

3 people conducting inventory of sea turtle nest on Sanibel. Black and white old photo
The early years of sea turtle monitoring on Sanibel
man standing on beach with vehicle that says 'caretta research inc'
Sea turtle researcher Charles LeBuff on Sanibel in 1989.

Smaller Nesting Females, Shorter Incubation Times

“Another interesting finding we had is that the average size of nesting females has decreased — a trend that has been occurring in multiple ocean basins and across species,” Weber said.

She explained one of the leading theories for smaller nesting female size is that it could be a result of an influx of new recruits (or younger females that have just reached reproductive maturity) to the nesting population, which again, could be linked back to successful conservation efforts started in the late 50s.

Additionally, SCCF’s analysis suggested that the average incubation time — or number of days the nest takes to hatch — has decreased by approximately four days.

“As sea turtle eggs incubate in the sand, environmental parameters such as humidity, temperature, and rainfall can affect embryonic development. Climate change-induced warming temperatures may be leading to increased temperatures within nests, speeding up the rate of development and decreasing incubation time,” Weber said. “Overall, analyses like this demonstrate the importance of sustaining long-term monitoring projects and how they can be used to identify trends within a species’ ecology.” 


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