Assessment of reproductive maturity of loggerhead sea turtles (Caretta caretta) found stranded along Veneto coastline, Northern Adriatic Sea

Knowledge on species’ reproductive biology is essential to understand population dynamics and manage conservation efforts. The present study analyses the reproductive maturity of loggerhead sea turtles (Caretta caretta) stranded along the Veneto coastline, northern Adriatic Sea, in the period January 2023 to February 2025. Focus was set on exploring the level of gonad maturity in stranded individuals using gonad gross morphology and histology, and investigating the relationship with size. Moreover, the aim was to understand any spatiotemporal trends in the stranding data with regard to the individuals’ size, sex, and maturity level. Lastly, the main sexual dimorphism in adult sea turtles, the difference in tail length, was analysed. Results found an evident seasonality with higher stranding frequency in the summer months, as well as high occurrence in stranding zones 7 and 6, which correspond to coastal areas close to inlets to the Venice lagoon. Based on gonad gross morphology, most individuals were assessed to be prepubescent (41.2%), followed by pubescent (25%) and mature individuals (20.6%). Mature individuals were either in condition preparing to breed, in regression after nesting season, or in quiescence. Histology of six individuals confirmed the macroscopic assessment of their maturity stage, although the analysis was compromised by tissue decomposition. Mature individuals were significantly larger than individuals with prepubescent and pubescent gonads, however the curved carapace length (CCL) of individuals with different gonad development showed a large overlap, demonstrating variability in size at maturity. Using generalized linear models (GLMs) and generalized additive models (GAMs), it was found that male loggerhead sea turtles begin to develop a longer tail than females between 50.2 and 56.2 cm, depending on which tail measurement was used. Overall, this study presents the first assessment of gonad development and reproductive maturity in loggerhead sea turtles in the northern Adriatic Sea and underlines the importance of this habitat for individuals in different phases of their life.