Growth patterns of Emys orbicularis across a range of aquatic habitats: a long-term study

Emys orbicularis is a semi-aquatic turtle with great longevity being able to reach 50 years. In this study, we estimated the growth rates (in carapace length and body mass) in a population of E. orbicularis from the northeastern Iberian Peninsula over a period of 23 years. We compared their growth rates among age groups, sexes, and years and across different types of habitats (small forest ponds, large forest ponds, and slow-flow streams). We hypothesized that the subpopulation that inhabits the small forest ponds may show slower growth rates because these habitats have lower solar exposure and lower water temperature. The study population showed sexual dimorphism in size, with females being larger and heavier than males. The analyses confirmed that the individuals from small forest ponds are smaller and grow at slower rates. Our results also revealed significant inter-annual variability in the growth rates of E. orbicularis, emphasizing the importance of conducting long-term studies of species with great longevity.