Assessment of Hatching and Emergence Success, Developmental Phases, and Pathology of Leatherback (Dermochelys coriacea) Embryos and Dead-in- Nest Hatchlings on St. Croix, US Virgin Islands

Northwest Atlantic leatherback (Dermochelys coriacea) sea turtle populations are endangered and have low hatching success compared to other sea turtles. Hatchling survival is an important element of their conservation. This longitudinal study assessed developmental phase and pathology of leatherback embryos and hatchlings at Sandy Point National Wildlife Refuge (SPNWR) on St. Croix, US Virgin Islands, in 2019 to identify patterns in mortality and lesions across a nesting season, and to make regional comparisons. Hatching and emergence success averaged 63.6% and 56.6%, respectively, and both differed significantly by month. 'Breakout' analysis was conducted on 41 nests and showed a preponderance of unhatched eggs lacking grossly evident embryological development (52%). Necropsies were performed on 79 unhatched and dead in nest individuals from 34 nests, and most (58%) had lesions including inflammation associated with micro-organisms (34%), renal mineralization (15%), mild multifocal skeletal muscle degeneration and necrosis (5%), and anatomic malformations (4%). Inflammatory lesions included chorioallantoitis, esophagitis, stomatitis, dermatitis, gastritis, and yolk sacculitis. These were associated with bacteria (n = 13), fungi (n = 4), or both (n = 7). Sex was determined histologically and was predominantly female (90%) with no males identified in nests laid after 3 April 2019. Although hatching success was higher in in situ relative to relocated nests, embryological development and lesion patterns were similar in both groups. Patterns of lesions observed in leatherback embryos and hatchlings did not differ across the season and are comparable to other Caribbean nesting sites. Future studies pairing 'breakout' and pathological analyses with assessments of potentially influential environmental and/ or maternal factors could help develop targeted strategies for improving hatchling production.