Effects of land use on fish assemblages in Patagonian low order streams

DI PRINZIO C.; CASAUX R.; MISERENDINO L.

ANNALES DE LIMNOLOGIE-INTERNATIONAL JOURNAL OF LIMNOLOGY

EDP SCIENCES S A

Año: 2009 vol. 45 p. 267 - 277

0003-4088

We assessed the effects of land use on the structure of stream fish assemblages in NorthwestPatagonia, Argentina. To this end, a total of 18 sites distributed in 15 streams were sampled during thelow water period. At each site, 26 regional and local scale variables were used to describe the environmentalconditions. The macroinvertebrate density, and the composition and abundance of fish were then recorded.Statistical associations between local assemblage structures and environmental variables were quantified bycanonical correspondence analyses. The results revealed that, at a regional scale, the fish assemblages wereprimarily determined by watershed features like altitude and catchment area, and by land use effects (exoticforest and pasture). Assemblage compositions were also related to some local-scale features such as watervelocity, food availability (density of benthic macroinvertebrates), instream characteristic and riparianfeatures. Also, the observed fish species richness was low. Overall, exotic salmonids largely dominated inthe samples both in numbers of individuals (98.9%) and in biomass (99.9%), whereas native fish (Hatcheriamacraei and Odontesthes hatcheri) were scarcely represented. Rainbow trout (Oncorhynchus mykiss) was themost abundant fish, and was present in all streams. Native species were restricted to five streams located inthe ecotone between the Andes and the steppe, where salmonids were also present. Salmonids were theonly fish at Andean streams which suggest the existence of a strong geographic segregation between nativeand exotic species. Some aspects related to the incidence of the introduced species in the structure of fishassemblages are discussed.