Introduction of exotic fish species and decline of native species in the lower Po basin, north‐eastern Italy

Abstract

ABSTRACTFreshwater ecosystems worldwide are experiencing native fish losses with severe threats to the conservation of freshwater biodiversity and ecosystem functioning, and the debate on whether the cause is biotic or abiotic disturbance is still open.Temporal variation in fish assemblages was analysed over an 18 year period in 14 waterways of the lowland backwaters of the Po River in north‐eastern Italy, which are important feeding, spawning and nursery sites for native fish.In 1991, 14 native and eight exotic species were collected. In less than 20 years 10 native species underwent local extinction, three of which –Rutilus pigus,Rutilus aula, andChondrostoma soetta– were endemic to the Padano‐Veneto District in northern Italy.Ordination of the data (MDS, CLUSTER, ANOSIM, SIMPER) showed a clear temporal gradient in fish community structure. After the establishment of the exotic predatorSilurus glanis, some native species significantly declined in abundance and biomass (i.e.Alburnus arborellaandScardinius erythrophthalmus) or disappeared (i.e.Rutilus aulaandTinca tinca). Moreover, exotic speciesCyprinus carpio,Ameiurus melas, andCarassius auratusfrom previous introductions, underwent significant changes in their abundance and biomass. No correlation was found between fish community structure and water quality parameters (BIOENV).The success of exotic species, particularlyS. glaniswhich thrived in this degraded habitat, seems to have led to the decline of native fish fauna in the canals of the lower portion of the Po River basin. Conservation strategies focusing on the containment of exotic species and habitat restoration are recommended.Copyright © 2013 John Wiley & Sons, Ltd.