Dati preliminari di abbondanza e distribuzione di Salmo fibreni Zerunian & Gandolfi 1990 nel bacino di Posta Fibreno (Italia Centrale): primo utilizzo del visual census

Preliminary abundance and distribution data of Salmo fibreni Zerunian & Gandolfi 1990 in the Posta Fibreno basin (Central Italy): first use of visual census - Lake Posta Fibreno and Stream Dova harbour Salmo fibreni Zerunian & Gandolfi 1990, an endemic taxon still quite unknown in its phenology and ecology. We report here a first attempt to quantitatively estimate the abundance of the lacustrine population of S. fibreni by means of the visual census method, generally considered as a non-intrusive technique and capable of providing ecological information otherwise not achievable. A total of 19 observations (snorkelling and scuba diving) during 1 year (September 2006-July 2007) in the lake zones presently frequented by S. fibreni were performed along transects of 100-130 m length by two observers. Densities of S. fibreni resulted to be negatively affected by light (1 single diurnal contact) and very low everywhere in the lake (mean 2 ind per 100 m, max 9 ind per 100 m), especially if compared to Rio Dova densities as derived from electrofishing. The distribution of S. fibreni within the basin seems to be strictly dependent on substrate composition, springs proximity, presence of flourishing aquatic vegetation. Immediate measures of conservation and support appear to be necessary, as the species individual numbers clearly point out a high risk of extinction.