Abstract
Bottlenose dolphins (Tursiops truncatus) exhibit delayed sexual maturity, with the onset achieved only after gaining the critical mass necessary to survive, as endothermic homeotherms in a highly conductive aquatic environment. However, various factors, such as population density, nutrition, and contaminants, can impact the age and length at which individuals achieve sexual maturity, which varies among species and populations. The purpose of this project was to analyze the ovaries of female dolphins that stranded dead in South Carolina waters, specifically through the assessment of ovarian corpora formed after ovulation, to establish sexual maturity relevant to age and length. The estimated age (ASM) and length (LSM) at sexual maturity was 8 years and 215 cm, respectively. Temporal analysis of a three-decade time span, from 1992 to 2022, indicated a trend of earlier maturation during the years 1992-2001 and 2012-2022 when compared to other years. The ASM and LSM of estuarine and oceanic dolphins were comparable. However, dolphins with human interaction (HI) had higher LSM estimates than dolphins without HI, suggesting possible differences in growth rates of healthy and sick individuals, as HI was used as a proxy for animal health. The maturity of stranded females was not associated with the season of stranding, stranding location, or the presence of HI. Total corpora count increased with age, which supports previous findings of corpora accumulation in bottlenose dolphins. Based on the accumulation rate, the calving interval was estimated to be 3.7 years. Based on a predictive model, animal body length and total corpora counts may serve as useful predictors of mature female age. In mature females, the left ovary weighed significantly more and accumulated significantly more corpora than the right ovary, suggesting skewed ovarian activity favoring the left ovary. A predictive model was created using animal body length and ovarian weights to predict maturity. These findings provide descriptions of bottlenose dolphin reproductive parameters and baseline estimates of the onset of sexual maturity among female dolphins in South Carolina. These estimates are critical to sound conservation and management efforts because reproductive parameters are susceptible to variation in response to population and environmental pressures.