Mario Mearelli

Bio: Mario Mearelli is an academic researcher from University of Perugia. The author has contributed to research in topics: Micropterus & Perch. The author has an hindex of 7, co-authored 14 publications receiving 203 citations.

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.

Diets of micropterus salmoides lac. and esox lucius l. in lake trasimeno (umbria, italy) and their diet overlap.

Abstract: The aim of this study was to gather information about the feeding habits of Micropterus salmoides Lac., an exotic species recently introduced into Lake Trasimeno and Esox lucius L., in order to determine the degree of overlap between the two diets. The stomachs of 179 largemouth basses and 125 pikes were examined. The index of diet overlap (α) was determined by using a Prominence Value (PV) of each food item, using Schoener’s formula. The value of the diet overlap index in the whole sample was 0.79. When the sample was divided in groups based on length, the index values were high and varied from a minimum of 0.623 to a maximum of 0.925. Based on theses results, a hypothesis of food competition between the two species in Lake Trasimeno could not be rejected.

The growth of pike (Esox lucius Linnaeus, 1978) in lake Trasimeno (Umbria, Italy).

Abstract: Abstract The growth of the pike ( Esox lucius L.) population of Lake Trasimeno was studied. A total of 166 specimens was captured in two monthly sampling series, from May 1993 to 1994 and from February to April 1998. There were 45 females and 79 males; nine age classes were present. Regression analysis between total length (TL) and weight ( W ) was W =0.0001×TL 3.0366 ; no significant differences between sexes were recorded. The parameter values for the von Bertalanffy growth curve for length were L ∞ =162.76 cm, K =0.089 yr −1 and t 0 =0.29 yr. An inverse Lee phenomenon exists for the 2-, 3- and 4-year-old age classes in the Lake Trasimeno population, indicating a differential mortality which favoured the survival of the larger individuals. One-year-old specimens were excluded from this phenomenon. Competition between pike and the exotic species largemouth bass ( Micropterus salmoides Lac.), recently introduced in Lake Trasimeno, could explain the differential mortality in pike, especially in the smaller specimens during winter.

Biotic indirect effects: a neglected concept in invasion biology

Abstract: Indirect effects involve more than two species and are defined as how one species alters the effect that another species has on a third. These complex interactions are often overlooked in studies of interactions between alien and native species, and their role in influencing biological invasions has been rarely considered. Based on a comprehensive review of the invasion biology literature, we examine the evidence for the occurrence of four of the most commonly documented indirect effects (apparent competition, indirect mutualism/commensalism, exploitative competition, and trophic cascades) in the invasion process. Studies investigating indirect effects in the context of invasion biology are relatively rare, but have been increasing in recent years, and there are sufficient examples to indicate that this kind of interaction is likely to be more common than is currently recognized. Whether indirect interactions are mediated by an alien or a native species, and whether they occur between ecologically similar or dissimilar alien and native species, depends in part on the type of interaction considered and no predictable patterns were detected in the literature. Further empirical studies will help to elucidate such patterns. At this stage, the inherent unpredictability of indirect interactions means that their impacts in relation to invasions are particularly challenging for land managers to deal with, and their role in invasions is a complex, but is a valuable area of investigation for researchers.

Reservoirs promote the taxonomic homogenization of fish communities within river basins

Abstract: Most studies analyzing patterns in biotic homogenization of fish communities have used large-scale approaches, while the community-level effects of species introductions and local extinctions within river basins have been sparsely analyzed. In this article, we examine patterns in freshwater fish α- and β-diversity in relation to the presence of reservoirs in a Mediterranean river (Guadiana river; Iberian Peninsula). We used fish samples from 182 river localities and 59 reservoir ones to address two main questions: (i) do reservoirs favor the establishment of invasive fish species?; and (ii) do reservoirs bear taxonomically homogenized fish communities? Although total species richness was not different between rivers and reservoirs, the latter had more invasive species and less native ones. Fish species found in reservoirs tended to be larger ones, but invasive species of any size showed higher preferences for reservoirs. Native species that were rare or absent in reservoirs were those that showed higher sensitivity to invasive species in rivers. Reservoir fish communities were taxonomically homogenized in relation to river ones, both when considering all fish species and using only natives or only invasive ones. Our results suggest that invasive species occupying reservoirs constitute an ecological filter excluding most native species from such systems. Invasive species in the study area are often widely introduced elsewhere, while native species found in reservoirs are congeneric and ecologically similar to those found in other Iberian studies. Thus, we conclude that reservoirs promote taxonomic homogenization at multiple spatial scales, while could also be promoting the functional homogenization of Iberian fish communities.

Non‐native fish impacts on Mediterranean freshwater ecosystems: current knowledge and research needs

Abstract: Non‐native fishes are often blamed for exerting adverse ecological impacts on native fishes, but the evidence is circumstantial and the true impacts remain largely unknown. This dilemma is particularly acute for freshwater ecosystems of the Mediterranean Region, where a high level of endemism (a biodiversity hotspot) makes native fish extinctions much more likely because of their small natural ranges. The aim of this paper is to review non‐native fish impacts, from genes to ecosystem level, in the fresh waters of the Mediterranean Region and identify gaps in knowledge that currently hamper effective conservation and management of native species and ecosystems. Most studies reviewed reported potential impacts rather than realised impact mechanisms, and these were conducted predominantly in the European part of the Mediterranean Region. No studies of realised impacts were found for three of the 15 most introduced fishes, which emphasises the need for evidence‐based studies of non‐native species impacts.

Rainbow trout in Europe: introduction, naturalization, and impacts.

Abstract: The rainbow trout (Oncorhynchus mykiss) is probably the most widely introduced fish species in the world. Since the first translocation outside of the range of its natural distribution, the species has been introduced into at least 99 countries and has established reproducing populations in many different parts of the world. The present review aims to synthesize the existing information on these translocations, with special emphasis on self-sustaining populations in Europe, where continuous introductions have in general not led to naturalization. Our survey produced a list of more than 130 confirmed or potential self-sustaining populations across 16 European countries. The highest abundance of such populations was observed in the Alpine foothills of central Europe where naturalization is not limited to modified waters less suitable for native salmonids but also occurs commonly in pristine and near-natural waters. There is no consensus on the reasons for the absence of self-sustaining populations of rainbo...

An update on the status of native and exotic freshwater fishes of Italy

Abstract: Summary An updated, corrected checklist of both native and established alien freshwater fish species in Italy is given based on molecular, morphological and biogeographical data. Some 12 native species, reported as conspecific with transalpine species in official Italian ichthylogical literature, are in fact endemics. Previous taxonomic confusion has resulted in the introduction of several alien species, either with official stockings or mixed in as impurities. Rehabilitated species include the cyprinids Scardinius hesperidicus, Scardinius scardafa and Telestes savigny from northern Italy, as well as Squalius ruffoi and the Telestes comes from southern Italy. Squalius albus is a junior synonym of S. squalus. The endemic gudgeon, previously assigned to the genus Romanogobio, is returned to the genus Gobio (G. benacensis). Phoxinus lumaireul is a junior synonym of P. phoxinus. Among the Salmonidae, Salmo cenerinus is a junior synonym of S. marmoratus, while Salmo farioides represents the trout species of the Adriatic lineage for which a neotype is designated. Thymallus aeliani represents the endemic lineage of grayling of the Adriatic populations. The esocid Esox cisalpinus is an endemic pike species and Esox flaviae is a junior synonym; the extensive exportation as well as the presence of this species throughout Europe is possibly due to humans. Among sculpins, Cottus scaturigo and C. ferrugineus are junior synonyms of C. gobio. The International Union for Conservation of Nature (IUCN) categories for native species of Italy are updated. At present, 52 native freshwater fish species are listed: 2 are extinct (Acipenser sturio and Huso huso), 12 are critically endangered, 7 endangered, 10 vulnerable, 3 near-threatened, 15 low concern and 3 data-deficient; 35 species are the result of human transfers. Among the 51 introduced species, 6 are recently established (Leuciscus leuciscus, Oreochromis niloticus, Poecilia reticulata, Xiphophorus helleri, Amatitlania nigrofasciatus, Hemichromis sp.), 37 are already established, 5 are probably established and 3 are non-established Chinese carp, maintained in the wild by intensive stockings. The family most involved is the Cyprinidae, with 22 alien and 20 native species.