Development of a fish-based index (FBI) of biotic integrity for French lakes using the hindcasting approach

Abstract The European Water Framework Directive clearly indicates that fish is one of the “quality elements” to be considered for the assessment of lentic systems. However, few fish-based indices (FBIs) of biotic integrity have been developed for lakes so far. Hence, the aim of our study was to develop such a tool for French lakes. Fish surveys, lakes natural environmental parameters, catchment-scale anthropogenic pressures, and local pressures were collected for 67 reservoirs and 24 natural lakes throughout France. After assigning fish species into trophic, reproductive, and tolerance guilds, we derived a set of metrics reflecting complementary aspects of community functioning and condition. Other community-level traits such as richness and evenness were added. These metrics were modeled vs. natural environmental variables and pressures. Reference conditions at each site were then assessed using hindcasting modeling. Separate indices were eventually obtained for natural and artificial lakes by combining selected metrics. Fifteen out of 73 candidate fish metrics, covering all three groups of functional traits, displayed a significant response to anthropogenic pressures. After removal of the redundant traits, the final indices for natural lakes and reservoirs included three and six metrics, respectively. Agricultural-related impacts were prominent for reservoirs, whereas for natural lakes urban and local pressures displayed the most significant effects.