Fish zonation and indicator species for the evaluation of the ecological status of rivers: example of the Loire basin (France)

Abstract

In the context of river alteration, ecologists are asked to develop tools for the assessment of river integrity. Fish are known to be good bioindicators of the ecological condition of rivers. The Loire basin (France) is often considered as relatively little impacted compared to most other large European systems. But curiously, no study clearly addressed the question of fish assemblages patterns in this system in order to assess this status. Thus, we studied fish assemblages along the river network in the Loire basin using self-organizing maps (SOMs) and we built a fish typology. Four basic assemblages were described and indicator species were identified. These assemblages varied in terms of individual species patterns as well as in terms of flow preference guilds and species richness. A discriminant analysis carried out on environmental variables revealed that they could be mainly determined by the slope, temperature and depth. Finally, fish assemblages were arrayed along a longitudinal gradient and roughly fitted the theoretical zonation expected in European rivers with the succession of brown trout (Salmo trutta fario), grayling (Thymallus thymallus), barbel (Barbus barbus) and bream (Abramis brama) zones in a downstream direction. Such patterns are still rarely observed in large European systems. However, the fish assemblage characteristic of the bream zone occurred more frequently than predicted on the basis of environmental variables. Such deviations between field data and theory suggest lotic-to-lentic shifts probably due to anthropogenic disturbances, especially in the grayling and barbel zones. In these river sectors, eurytopic and limnophilic species tend to replace rheophilic ones. Finally, the method used in this study to investigate fish patterns may be helpful to detect disturbances and may serve as a tool for the establishment of management plans

Assessing the freshwater distribution of yellow eel

“…Faced with the widespread problem related to the difficulty of obtaining reliable and usable data sets, recent advances in conservation biology have suggested that presence-absence data are particularly suitable for the assessment of species distribution in a conservation context (MacKenzie, 2005;Vojta, 2005). Despite the simplicity of such input data, they can provide reliable information for analyzing species distribution, especially in a conservation context (Joseph et al, 2006), and above all the distributions of fish assemblages (Ibarra et al, 2005;Lasne et al, 2007aLasne et al, , 2007b, certain fish species (Oberdorff et al, 2001;Pont et al, 2005), migratory fishes (Eikaas and MacIntosh, 2006) and eel (Broad et al, 2001;. In fish, electrofishing methods are among the most common ways of sampling fish.…”

Strategy of recreational anglers and estimated eel (Anguilla anguilla) catches in a large European catchment basin, the Loire (France)

“…The Loire itself is a relatively freeflowing river, and there are no significant barriers to migration in its lower reaches (the first one is > 500 km upstream of the tidal limit). Consequently, the Loire basin is often considered as being less impacted than other large river systems in Europe (Lasne et al, 2007). In contrast, most of its tributaries have been largely regulated by barriers that fish may or may not be able to get through.…”

“…With regard to the continental yellow eel stage in the Loire, the eel distribution could be obtained from the sampling network of the ONEMA (the French National Office for Water and the Aquatic Environment), which covers 135 sites around the Loire catchment basin. This identified the most important eel sectors, and provided an indication of current densities, and of spatial and temporal trends (Lasne et al, 2007;Lasne and Laffaille, 2008). These densities made it possible to identify the administrative areas (departments) around the Loire that were most implicated in the management of the species.…”

“…Recreational fishing has economic, social and cultural roles. Finally, recreational fishing must clearly be taken into account when considering the measures for managing fisheries introduced since the establishment of the eel management plan at the EU level (Council Regulation EC No 1100/2007of 18 September 2007. So far, there has been little investigation of recreational eel fishing, although this has not prevented the introduction of some management measures.…”

Structure of endemic fish assemblages in the upper Yangtze River Basin

“…In fish ecology, the structure of fish assemblages depends on many interacting factors and can be quantified by summarizing species richness, composition and feeding guilds (Karr, 1981). Classification of sites (or areas) based on fish species assemblages has been elaborated for many lotic systems (Konan et al, 2006;Park et al, 2006;Kruk et al, 2007;Lasne et al, 2007). Modelling the composition of fish assemblages on the basis of biotic and abiotic environmental descriptors is an important aspect of the management of aquatic ecosystems.…”