Clutch Size, Clutch Frequency, and Egg Characteristics of Diamond-Backed Terrapins (Malaclemys terrapin) in Southwestern Louisiana

Abstract - The reproductive output of Malaclemys terrapin (Diamond-backed Terrapin) is highly variable across its geographic range. While much of the literature is based on populations from the Atlantic coast of the United States, little reproductive-output data exists for the Gulf of Mexico populations. We captured female Diamond-backed Terrapins in southwestern Louisiana and assessed their reproductive output using radiographic- and ultrasound-imaging techniques. X-rays identified that average clutch size was 7.2 and average egg width was 21.9 mm. We revealed a positive relationship between female size (plastron length) and both clutch size and egg width, but no relationship between egg size and clutch size. Ultrasound imaging in a subset of individuals revealed large pre-ovulatory follicles and fully shelled eggs concurrently in females, indicating the potential for at least 2 clutches annually in this region. Our results suggest Diamond-backed Terrapins in southwestern Louisiana show variation in reproductive output compared to other populations at similar latitudes, indicating the need for additional study within and between populations in the region.