Influence of the Fish Introduction in Lakes of the Arid Southern Patagonia

Abstract

Rainbow trout (Oncorhynchus mykiss) was introduced in most lakes of Patagonia, generating concern about its impact on the receiving communities. However, the information about the effects of trout in stocked lakes of this region is still fragmentary. We conducted a comprehensive comparative study of fishless and stocked lakes of the arid southern Patagoniato analyze the extent of trout effects on the community composition, primary productivity and food webs, considering also contrasting climatic conditions (wet and dry years). Rainbow trout shaped the community of pelagic crustaceans, affecting both species’ dominance and size structure. Stocked lakes also showed substantial differences in phytoplankton structure,and higher abundances of microplanktonic cyanobacteria, probably caused by top-down effects. These changes were more pronounced during dry periods, indicating the concomitant effects of trout introduction and climate fluctuations. Trout also generated alterations in food webs, forcing their main prey (amphipods) to shift from predominantly pelagic to benthic/littoral feeders. Differences in stable isotope values also indicate changes in the habitat coupling when trout were present. We discuss results from a conservation perspective, considering the potential consequences for waterbirds, mainly for the critically endangered hooded grebe (Podiceps gallardoi), which have their reproductive habitat in the analyzed aquatic systems.