Comunitats íctiques dels rius mediterranisrelació amb les condicions ambientals, Les

Resumen

Two essential aspects of Mediterranean freshwater fish conservation research are addressed in this dissertation: - First, the biology (growth and reproduction) of the more common cyprinids species, Barbus graellsii, B. haasi, B. meridionalis, Chondrostoma miegii and Squalius cephalus was studied. - Second, temporal and spatial changes in fish community structure related to variability of environmental conditions were monitored in several Catalonian river basins: Aigua dOra river (Llobregat basin), Llobregat river (Muga basin), Matarranya river (Ebro basin) and Ripoll river (Besòs basin). Field work was done four times a year, in the spring, summer, autumn, and winter, with a total of 13 sampling periods in the Matarranya river (from the summer of 1985 to the summer of 1988), and 11 in the Aigua dOra, Llobregat and Ripoll rivers (from the winter of 1987 to the summer of 1990), and it consisted of sampling for biological study and quantitative estimates of fish communities. The five studied cyprinid species (B. graellsii, B. haasi, B. meridionalis, S. cephalus, and C. miegii) fell into one of two possible life history patterns: - Fish populations inhabiting temporal Mediterranean rivers present a periodic strategy characterized by large size, slow growth, and moderate reproductive effort. - Fish populations inhabiting permanent Mediterranean rivers present an opportunistic strategy characterized by middle size, fast growth and high reproductive effort. Mediterranean fish communities are highly persistent and their stability varies from moderately stable, in permanent Mediterranean rivers, to highly fluctuant in temporal Mediterranean rivers. In all cases, persistence of introduced species is very small and the populations of these species fluctuate widely. Secondary production of Mediterranean river fish communities is very high (the one in the Matarranya river is the highest recorded in scientific literature) and P/B ratios are directly correlated with the reduced amount of the annual discharge in relation to the mean annual discharge characteristic of each river."