Invasion of Montpellier snake Malpolon monspessulanus (Hermann, 1809) on Mallorca: new threat to insular ecosystems in an internationally protected area

Abstract

Over the last decade, three alien snake species have been reported in three of the main islands of the Balearic Archipelago (Spain): Mallorca, Ibiza and Formentera. These introductions are considered a threat to the native biota and are associated with the nursery trade from the Iberian Peninsula. The Montpellier snake Alalpolon monspessulanus (Hermann, 1809) was first reported in Mallorca in 2006. Since then, a significant number of observations and captures of this species have been reported around the natural park of s' Albufera de Mallorca. Most of these captures correspond to adult specimens, and the snout-vent length (SVL) values of the entire population ranged from 31.5 to 137.0 cm (n = 69). The observed operative sex ratio was 1.00:1.56 (males:females) and adult males reached larger sizes than adult females. In terms of reproductive biology, five adult females presented oviductal eggs. Finally, skeletal growth marks in the ectopteiygoid bone were analyzed, giving results of age from 1 to 20 years old. The significant number of observations, the great sizes and ages reached by some individuals and the detection of gravid females could indicate that the population is well established, fully naturalized and threatening insular ecosystems. This naturalized population is the only insular population of M. monspessulanus located in the western Mediterranean. The proximity of the invasion event to sites of environmental relevance such as those included at Natura 2000 network and Ramsar wetland promotes the idea of assessing the impact of this alien species on native biodiversity. There is an urgent need of carrying out future control actions and implementing biosecurity measures in order to prevent new arrivals of this and other alien species into the Balearic Islands.