Sylvain Mastrorillo

Predicting local fish species richness in the garonne river basin

Abstract The aim of this work was to predict local fish species richness in the Garonne river basin using three environmental variables (distance from the source, elevation and catchment area J. Commonly, patterns of fish species richness have been investigated using simple or multi-linear statistical models. Here, we used backpropagation of artificial neural networks (ANNs) to develop stochastic models of local fish diversity. Two independent data collections were used, the first one to build and test the model; the second one to validate the model. Correlation coefficients between observed values and predicted values both in the testing and the validation procedures were highly significant (r = 0.904, P

Factors influencing the spatial distribution patterns of the bullhead (Cottus gobio L., Teleostei Cottidae): a multi-scale study

Abstract.We used general linear modelling to assess the influence of environmental variables on the spatial distribution patterns of the bullhead (Cottus gobio) at stream system, site, and microhabitat scales in southwestern France. Bullheads occurred at 67 sites (out of 554 sampling sites), chiefly close to the source, in small and shallow streams. Population density at a site was primarily influenced by thermal conditions. Stream width was negatively related to the probability of presence of bullheads within the stream system, but positively related to local density, showing that bullhead density could increase within a range of stream width, but that wider rivers were unsuitable. Slope was negatively correlated to bullhead’s occurrence and local density, and depth was negatively correlated to local density and microhabitat use, suggesting that bullhead’s shimming performance was weak under greater erosive forces. Therefore, the most significant results suggested that the distribution of populations and individuals was first governed by the suitability of physical and hydraulic habitat, then population dynamics at a site was mainly governed by the thermal regime. Multi-scale studies of factors influencing a species’ distribution thus allow to integrate patterns observed at different scales, and enhance our understanding of interactions between animals and their environment. Such models are essential in the exploratory phase of fundamental and applied investigations, because they help to target further research, and they should influence the measures to be taken in field surveys or conservation plans.

Gravel pits support waterbird diversity in an urban landscape

We assessed the benefit of 11 gravel pits for the settlement of waterbird communities in an urbanized area lacking natural wetlands. Gravel pits captured 57% of the regional species pool of aquatic birds. We identified 39 species, among which five were regionally rare. We used the Self-Organizing Map algorithm to calculate the probabilities of presence of species, and to bring out habitat conditions that predict assemblage patterns. The age of the pits did not correlate with assemblage composition and species richness. There was a positive influence of macrophyte cover on waterbird species richness. Larger pits did not support more species, but species richness increased with connectivity. As alternative wetland habitats, gravel pits are attractive to waterbirds, when they act as stepping stones that ensure connectivity between larger natural and/or artificial wetlands separated in space.

Environmental factors influencing the regional distribution and local density of a small benthic fish: the stoneloach (Barbatula barbatula)

We investigated the relationships between different environmental variables and the spatial distribution patterns of the stoneloach (Barbatula barbatula) at the stream system, the stream site, and the mesohabitat (riffle/pool) scales in south-western France. Stoneloach occurred at 240 sites (out of 554 sampling sites), chiefly close to the source, in areas at low elevation and with weak slopes. Population density at a site was primarily influenced by physical conditions. Stream width was positively related to the probability of presence of stoneloach within the stream system, but negatively related to local density. These results indicate that stoneloaches can occur in a wide range of streams, but they are less abundant in wide rivers, probably because of lower habitat heterogeneity. Slope was negatively correlated to both fish presence at the regional scale and local density, suggesting that stoneloach’s swimming performance were weak under greater erosive forces. These results suggested that the distribution of populations and the density of stoneloach were governed by the suitability of physical habitat. Multi-scale studies of factors influencing a species’distribution allow to integrate patterns observed at different scales, and enhance our understanding of interactions between animals and their environment. The use of few pertinent variables in successful final models could reduce the effort and cost of data collection for water management applications.

Environmental determinants of Great Cormorant (Phalacrocorax carbo) distribution in small man-made waterbodies - a case study of gravel pits in southwest France

In the Midi-Pyrénées region (southwest France), the increasing number of gravel pits has allowed the wintering of numerous species of waterbirds such as Great Cormorants (Phalacrocorax carbo). The debate about cormorant predation on fish stock has been sufficiently strong to have resulted in reductions in cormorant numbers by control shooting. In this context, cormorants were studied during winters 1996/1997 and 1997/1998xa0at two gravel pit sites in the Garonne floodplain. Human disturbances and fish densities were found to be the main parameters determining the abundance of fishing cormorants. This work will help to prompt further research and the development of a management strategy for this species.