Les peuplements de poissons de la Camargue

Abstract

Fish communities in the Camargue wetlands, both temporary and permanent marshes as well as irrigation and drainage canals, were studied from 1977 to 1980. The main part of this work was carried out in wetlands isolated from direct contact with the sea by a dike, the Digue à la mer. Three major types of wetlands and their associated fish species are described in the Camargue : the freshwater (0-5 g/1 C1￣ ), the brackish (5-16 g/1 C1￣ ) , and the very brackish (16-35 g/1 C1￣ ) . A significant relationship (P< 0.01) was found between the species richness and the surface area. The slope of this regression (0.134) is lower than that found for other aquatic systems. Four associations of fish were determined and their meaning is discussed. The biomass of temporary freshwater marshes ranged between 13 to 76 kg/ha and was much lower than those found in the small freshwater canals : 112 to 2 544 kg/ha. Common carp, Cyprinus carpio L., is the dominant species in freshwater wetlands (70 to 85 % of total biomass). A space partitioning between the immature and the adult carp is described. In one waterbody studied south of the Digue à la mer, linked temporarily with the sea, the fish community composition underwent frequent and rapid changes according to the variations of environmental factors. The salinity appeared to be the most important factor affecting diversity and eveness of the fish community in this etang. A canonical analysis was used to determine which of the environmental factors had the greatest impact on the abundance of the different fish genus. Only 46.2 % of the fish species studied reproduce in the Camargue, while 35.9 % migrate to the sea for spawning. The importance of a link with the sea as well as that of a sound water management plan for the Camargue as a whole are pointed out.