Fish assemblage of a Pampean shallow lake, a story of instability

Abstract

The aim of this study was to analyze the temporal long term variability of fish assemblage in Chascomús Lake. Data acquisition was based on documented historical research fishing records and experimental fishing program performed from 1999 to 2013. Fish assemblage composition showed a strong temporal variability. Planktivorous species such as Platanichthys platana, Odontesthes bonariensis and Parapimelodus valenciennis accounted for the 70 to 80% of relative abundance becoming alternatively dominant. The iliophagous Cyphocharax voga, the forth dominant species, shared with P. valenciennis the pattern of change in their relative abundance along time. O. bonariensis and P. platana showed high fluctuations in their representation from dominant to almost disappearance during the considered period. Cluster analysis allowed the identification of four different groups of fish assemblage configuration. Two of them grouped the data from historical studies meanwhile the other encompasses the samples taken between 1999-2012, being the discriminant species the mentioned above. Water level, critical temperatures and man basin modifications are discussed as main drivers of species relative abundance shifts. The study highlights the importance to build a long-term assessments to understand how fish assemblage modifications are linked to the typical pampean floods and drought cycles coupled with unfavorable thermal conditions and water management impacts.