Ichthyofauna of Lake Albufera of Valencia (Spain): past and present status.

Despite of the traditional socioeconomic importance of fisheries in Lake Albufera of Valencia, documented since the XIII century, there is an absence of long-term and comparative studies, and recent studies on the composition and ecological relevance of its fish assemblages. Available data are almost obsolete or fragmentary, and mainly based on qualitative analyses of species composition or on commercial captures. In consequence, an exhaustive historical review of the ichthyofauna data together with fishery records were analysed, and additionally fish communities were studied during summer 2000 and spring 2002. The aim is to determine the present status and fish changes since first records in 1865, and ascertain the influence of fish associations on the lake ecology. Results pointed out: a) a remarkable reduction in fish species richness, especially from the 1950s to 2002; b) a noticeable increase in the populations of exotic species, mainly Gambusia holbrooki and Lepomis gibbosus, that replaced to autochthonous species, such as Aphanius iberus, Barbus bocagei, Chondrostoma arrigonis or Valencia hispanica; c) that since the decade of 1950, mugilid captures increased (from 80 to 490 t year-1) in detriment of species, such as Anguilla anguilla or Dicentrarchus labrax. This trend agrees with the severe eutrophication, dissapearance of submerged macrophytes and over-fishing of these species in earlier periods; d) seasonal cycles were observed for the specific composition of the captures, which is related to each species population dynamics (common in coastal lakes) and to manipulation of the lake water renewal for rice cultivation. The highest commercial fish captures occurred between October and January, which reduced the predation on macrozooplankton and had consequences on the lake food web and water transparency, e) a relationship between fish assemblages and the lake trophic state was observed. The progressive anthropogenic eutrophication of the lake, the uncontrolled introduction of exotic species and scarce conservation and management of the lake and surrounded ecosystems, as well as of its fish resources, are pointed out as some of the main causes for the changes observed in its ichthyofauna. 06 Blanco 2/5/06 08:48 Pagina 45