Indagine sulla popolazione di luccio (Esox cisalpinus Bianco & Delmastro, 2011) del Lago Trasimeno condotta attraverso l’analisi di un campione di riproduttori selvatici

Cisalpine pike Esox cisalpinus is a species native to both Italian biogeographic districts, considered nowadays in strong decline throughout its native range. Also in the Lake Trasimeno, considered as a very suitable environment for the species, a progressive reduction of the population has been recorded during the last decades. The aim o this study was to investigate some still little-known biological aspects of E. cisalpinus, such as age class structure, growth and condition and their variation over time. The research was carried out on 3248 specimens (1722 females and 1526 males), collected from 2008 to 2017 by the Ichthyogenic Center of Lake Trasimeno. The pike population of the Lake Trasimeno was characterized by a strong sexual dimorphism in growth, with females reaching the maximum size of 103 cm and 15 years, while males grew only up to 70 cm and 8 years. The Proportional Stock Density Index showed an ongoing, gradual ageing process of the sample. The condition, assessed through Relative Weight (Wr) can be considered satisfactory (mean values: males=108.4, females=119.0), even if the mean values tended to decrease over time in both sexes. Back-calculation revealed the possible presence of a size-selective mortality that affected the smallest individuals in the first age classes in the males. On the other hand, the largest females in the same age classes seem disadvantaged. The results of this study, crossed with the environmental data analysis, suggested that water level fluctuations probably played a key role in the dynamics of pike population of the Lake Trasimeno.