Interannual Fluctuations in Mean Straight Carapace Length (SCL) of Nesting Kemp’s Ridley Sea Turtles Signal Demographic Shifts at Rancho Nuevo Sanctuary, Tamaulipas, Mexico

The critically endangered Kemp’s ridley sea turtle (Lepidochelys kempii) population experienced a catastrophic decline from a peak in 1947 to a low in 1985, followed by exponential growth prior to 2010. However, the Deepwater Horizon (DWH) oil spill caused a demographic setback. Monitoring nesting female straight carapace length (SCL) is crucial for assessing population structure and recovery. We analyzed interannual variation in SCL of nesting females at Rancho Nuevo Sanctuary, Tamaulipas, Mexico, during the 2018–2023 nesting seasons. A total of 191 females were measured, and a comprehensive statistical analysis was performed to validate the use of parametric tests. One-way ANOVA revealed significant differences in mean SCL among years (p < 0.001). The lowest seasonal SCL means were in 2020 (59.01 ± 1.79 cm) and 2022 (60.68 ± 1.47 cm), while the highest SCL means occurred in 2018 (62.77 ± 1.81 cm), 2019 (62.01 ± 1.56 cm), 2021 (62.19 ± 1.47 cm), and 2023 (61.75 ± 2.07 cm). There was no significant linear decline in mean SCL from 2018 to 2023 (p = 0.78). These results suggest short-term interannual variability rather than a consistent shift in body size structure, providing updated baseline information for post-DWH population monitoring and future recruitment assessments.