Fish assemblage changes in spring-fed irrigation ponds with reference to revetment construction and exotic piscivorous fish: A comparison with a decade ago

Abstract

Fish assemblage structure in spring-fed irrigation ponds in the Shigenobu River watershed (Ehime Prefecture) was compared between two periods, 1998-1999 and 2008, to examine effects of revetment construction and exotic largemouth bass (Micropterus salmoides). Two of the 11 study ponds were 'altered ponds, where bank revetment was constructed during the decade, whereas another pond was 'bass pond, where largemouth bss had established a self-reproducing population. Comparisons of species richness, density of each species and assemblage structure revealed that the most distinct change occurred in the bass pond, where most species other than largemouth bass showed drastic declines in population density. On the other hand, distinct fish-assemblage changes specific to the altered ponds were not found, despite considerable habitat changes due to the revetment construction work. Our data also revealed that two species, Tanakia lanceolata and Gnatho-pogon elongatus elongatus, which had been found from six and two ponds, respectively, disappeared in 2008. These disappearances may suggest an overall degradation of irrigation-associated aquatic systems (river-pond-ditch-paddy: alternative habitats for floodplain-adapted fishes) as fish habitat.