Unsaturated fish assemblages in rivers of the North-Western France : potential consequences for species introductions

Abstract

Introductions of freshwater fish into French rivers have been carried out with increasing frequency in the last decades. Thus, the potential impact of these introductions is of major concern for biologists and fishery managers. Knowledge of the degree of saturation of a community provides an important basis for understanding how the community reacts or will react to the introduction of new species. In this paper, we compare local and regional freshwater fish species richness in similar sizes tributaries and coastal rivers located in the same biogeographic region (North-Western France). We show 1) that species richness is greater for tributaries than for coastal rivers on both local (station) and regional (catchment) scales, and 2) that, whatever the rivers studied (tributaries or coastal rivers), there is a significant, positive linear relationship between local species richness and regional species richness. These findings suggest that local, and probably regional, freshwater fish communities in North-Western French rivers are unsaturated and thus, that major impacts on the community, such as short-term extinctions, are not to be expected. However, competition for food and space, prédation, introduction of exotic parasites and diseases, could also affect some native species.

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

“…The degree of degradation in the fish community of the Tiber watershed also appears to be related to the longitudinal gradient. Although studies on the environmental organization of freshwater fish communities in Italy are still limited, some of the trends revealed by our analysis have been described for other geographic areas (AADLAND, 1991;BELKESSAM et al, 1997;LOBB and ORTH, 1991;SCOPPETTONE, 1993;COLLARES-PEREIRA et al, 1995;GODINHO et al, 1997;GODINHO and FERREIRA, 2000). The upper part of the Tiber River basin consists of cold lotic environments, usually characterized by steep gradients.…”

Effects of natural and anthropogenic environmental changes on riverine fish assemblages: a framework for ecological assessment of rivers

“…Relative to this point, results of different studies previously detailed above show that local and regional fish communities are usually not saturated with species and are capable of supporting greater number of species if the pool of potential colonists and the rate of colonization from that pool was increased by species introduction (Belkessam et al, 1997;Angermeier and Winston, 1998;Oberdorff et al, 1998;Gido and Brown, 1999). These results strongly suggest that competition does not set the species saturation level in the assemblages studied and thus that competition is not a major force structuring these fish assemblages.…”

“…competition, predation, disturbance) were the focus of studies seeking to explain local fish assemblage structure (Schlosser, 1995), emphasis on the role of regional processes has increased as some studies have demonstrated their pervasive role in shaping local assemblages Whittier et al, 1988;Hugheny and Paugy, 1995;Hugueny et al, 1997;Belkessam et al, 1997;Angermeier and Winston, 1998;Oberdorff et al, 1998). Consequently, complete answers for the explanation of local fish assemblage richness and structure must address the relative importance of large-scale processes, which determine the species available to occur locally and small-scale processes, which should limit the number of species that actually occur locally (Angermeier and Winston, 1998).…”

“…The richness and structure of local fish assemblages has been linked to factors ranging from geomorphology and climate (Nelson et al, 1992;Whittier et al, 1988;Matthews and Matthews, 2000;Tejerina-Garro, 2001), to richness of regional species pool (Hugueny and Paugy, 1995;Hugueny et al, 1997;Belkessam et al, 1997;Angermeier and Winston, 1998;Oberdorff et al, 1998;Gido and Brown, 1999). Concerning this last relationship (local/regional richness) the emerging pattern is that few fish assemblages are trully saturated (Hugueny andPaugy 1995, Hugueny et al, 1997;Belkessam et al, 1997;Oberdorff et al, 1998). For example, working on local fish assemblages of coastal streams of North-Western France found that these assemblages were unsaturated with species and with individuals and that inter-annual changes in populations were not strongly affected by densities of co-occurring species.…”

Variabilité à moyen terme des peuplements de poissons des cours d'eau bas-normands

“…En effet, chacune des espèces qui compose les peuplements étudiés réagit de façon différentielle aux variations environnementales (différence dans : les périodes de ponte et de recrutement, la distribution sur le gradient vertical, les habitats, la taille des individus et leurs vagilités...) et contribue de la sorte à faire augmenter la variabilité du peuplement à mesure que l'on augmente la durée du suivi. Par ailleurs, à l'échelle locale, les peuplements de poissons des cours d'eau semblent dépendre, en partie, de processus qui s'opèrent à l'échelle régionale (HUGUENY et PAU G Y, 1995 ;BELKESSAM et al, 1997 ;OBERDORFF et al, 1998). …”