# Smaller Size of Nesting Loggerhead Sea Turtles in Northwest Florida

## TL;DR

Loggerhead sea turtles in northwest Florida are getting smaller, which could affect their ability to reproduce and recover as an endangered species.

## Contribution

This study provides new empirical data on body size trends and their reproductive consequences in a numerically small loggerhead sea turtle population.

## Key findings

- Approximately 9% of nesting turtles were below the minimum size for reproductive maturity.
- Larger turtles laid larger clutches but faced higher nest loss due to wave wash-out.
- Each 1 cm increase in turtle size correlated with one additional egg per clutch.

## Abstract

Tracking body size distribution within a population provides useful information on demography, population growth trajectory, and size class- or stage-specific threats. Using multi-decadal datasets, several sea turtle monitoring programs have reported a global declining trend in the average body size of adult female turtles. This is concerning as smaller sizes could be an indicator of reduced foraging habitat suitability, which could have implications for reproductive output. In numerically small populations, such changes in reproductive output have the potential to slow population growth rates. This project investigates the current body size distribution of loggerhead sea turtles nesting in northwest Florida—among the smallest populations (numerically) in the southeastern United States—as well as body size-related consequences for nest site selection and hatchling production. Since 2016, approximately 9% of encountered turtles were below the minimum size at reproductive maturity currently adopted by U.S. management agencies. In addition, larger turtles laid larger clutches but also lost more nests to wave wash-out. Understanding the cause of reduced adult body sizes in sea turtles and its potential consequences for population-scale hatchling production is crucial for informed conservation management of these imperiled species.

The distribution of individual body sizes within a population can have substantial impacts on recovery estimates for endangered species. Recent studies have observed a reduction in the size of nesting sea turtles with potential implications for fecundity. To investigate the size of reproductive individuals and subsequent impacts on hatchling production for loggerhead turtles in northwest Florida, we evaluated a seven-year dataset from St. George Island, Florida, USA—the dominant nesting site in this region. Morphometric measurements and GPS locations were collected during nighttime surveys, whereas nest disturbances and hatchling production were reported from morning surveys. Mean minimum curved carapace length (CCLmin) was 94.3 cm ± 5.7 cm SD (range: 80.2–109.1 cm). Out of 232 individuals, 9.1% fell below the 87 cm CCLmin threshold currently adopted by U.S. agencies as the minimum size at maturity. For each 1 cm increase in CCLmin, an increase by 1 egg was observed in clutch size, and wash-out rates increased by 0.52%. Though the largest turtles laid the largest clutches, these nests also had a greater probability of wave wash-out, potentially moderating overall hatchling production from these individuals. These results highlight size-mediated factors related to fecundity—important elements for demographic modeling and management decisions.