Six new non-native turtles in Portugal: A growing threat apart from the Red-Eared slider and Chinese stripe-necked turtle

Abstract

We report the first records of non-native freshwater turtles in Portugal, highlighting the growing diversity of species introduced in addition to the known Trachemys scripta and Mauremys sinensis. In 2024 and 2025, we surveyed 39 sites across Portugal and confirmed the presence of seven non-native species at seven sites. While T. scripta remained the most frequently recorded species (n = 68), M. sinensis, Graptemys pseudogeographica and different species of Pseudemys, were also captured, especially in Lisbon and Sintra. Remarkably, a high number of M. sinensis juveniles (n = 12) were captured, which could be explained by reproduction in nature. Notably, we documented the first evidence of nesting behaviour by G. pseudogeographica in Sintra, indicating the potential for this species’ establishment in the wild. These findings suggest that both illegal and legal non-native turtle pets are being released into Portuguese ecosystems. Our results highlight the need for broader preventative measures, as other introduced species may follow similar invasion pathways with unknown ecological impacts.