Native and Exotic Fish Species in the Tiber River Watershed (Umbria – Italy) and Their Relationship to The Longitudinal Gradient

Abstract

In this study we examine the spatial variations in the fish communities in the Tiber River watershed, including both native and exotic species. Its main objectives were to assess the quality of fish communities of this area and to verify if factors of fish community disturbance are constant over the basin or if they change along the river gradient. The level of degradation was evaluated according to the ratio between the number of native fish species and total number of species (ZIC = Zoogeographic Integrity Coefficient). A total of 37 fish species was found, 13 native and 24 exotic (64.86%). Cyprinid is the prevailing family with 15 species (7 native, 8 exotic). The species most frequently introduced are cyprinids, followed by salmonids (4 species) and gobids (3 species). Of the 24 exotic species only 11 (45.83%) can be considered intentionally introduced by man: the proportion of intentionally introduced transplanted species (66.67%) is considerably higher than the translocated species (33.33%). There is a correlation between the longitudinal gradient of the river, the morphological evolution of the riverbed and decline in water quality. High ZIC values were related to higher elevation, greater slope and better water quality. As the size of the river increases the fish communities appear to be ever-more dominated by species of exotic origin, whose number progressively increases with the worsening of the water quality and downstream movement. The number of native species is the greatest in the middle reaches of the rivers, and decreases both upstream and downstream. Compared to the introduced species, the native species tend to stay upstream and are often the only species found in the headwaters. The number of introduced species increases downstream. We have also found differences among translocated and transplanted species: the first ones tend to favor the middle reaches of the rivers, while transplanted species seem to prefer the downstream sectors. In almost all cases, the sampling station immediately below an impoundment has the lowest ZIC values in comparison to the river stretches above the dam. Our preliminary results suggest that characteristics of fish community alterations depend on the type of river sector involved; the small rivers of the basin are a refuge zone for the native community and are currently of fundamental importance for maintaining biodiversity.Key-words: introduction, exotic species, fish community, Tiber River, longitudinal gradient, Zoogeography Integrity Coefficient. ESPÈCES PISCICOLES INDIGÈNES ET EXOTIQUES DU BASSIN VERSANT DU TIBRE (OMBRIE ITALIE) RÉSUMÉCette étude examine la variation spatiale des communautés piscicoles du bassin versant du Tibre en prenant en considération les espèces indigènes et exotiques. L'objectif principal est d'examiner la qualité des peuplements piscicoles du bassin et de vérifier si les facteurs de détérioration des peuplements piscicoles sont constants ou variables le long du gradient longitudinal. Le niveau de détérioration de la communauté...

Status ofPseudorasbora parvain the Tiber River Basin (Umbria, central Italy) 20 years after its introduction

“…The study area is the Umbrian section of the Tiber River Basin (8412 km 2 ) (Figure 1) (Lorenzoni et al, 2006). This area includes many tributaries of the Tiber River, the most important of which are the Nestore (watershed = 1033 km 2 ), Paglia (1338 km 2 ), Chiascio (5963 km 2 ), and Nera (4280 km 2 ) rivers.…”

“…The degradation of environmental conditions in these areas is made worse by the presence of many water catchments for irrigation purposes also aggravates in those areas (Carosi et al, 2015). The Nestore River presents a broad variation in conductivity and EBI, with the latter fluctuating between III and IV water quality classifications, that indicate very high pollution levels (Lorenzoni et al, 2006). Only in recent years there has been a gradual improvement of environmental quality in this area (Carosi et al, 2015).…”

“…The hydrogeological characteristics and the high incidence of human activities adversely affect the water quality in these basins. Waterways that run through predominantly impermeable lands, such as the Nestore River, show very marked flow rate fluctuations (Lorenzoni et al, 2006); in times of drought the modest flow rates produce a greater concentration of pollutants. The degradation of environmental conditions in these areas is made worse by the presence of many water catchments for irrigation purposes also aggravates in those areas (Carosi et al, 2015).…”

“…The topmouth gudgeon is totally absent in the Nera River Basin . This basin is predominantly mountainous with its rivers showing the best water quality among all the watersheds considered in the study area (Lorenzoni et al, 2006). Two causes might be invoked for this absence: (i) the presence of numerous barriers in the water courses of this catchment that might impede the expansion of this species from the Tiber River; and (ii) environmental characteristics, more suited to salmonids rather than to cyprinids.…”

“…From these two first locations P. parva expanded rapidly in all directions. In 20 years this species invaded the middle and lower reaches of many watercourses of the Tiber catchment and it is still spreading throughout the Tiber River Basin (Lorenzoni et al, 2006 through spontaneous successive colonizations. At the end of the 1990s, the first specimens of P. parva were collected in Lake Trasimeno (Ghetti et al, 2007).…”