Potential impacts of non-native channel catfish on commercially important species in a Japanese lake, as inferred from long-term monitoring data

1. Biological invasions are among the most serious threats to freshwater biodiversity. Analysis of long-term data can be a positive first step toward properly identifying the ecological and economic damage caused by invasive species. This study assessed the potential impacts of invasive channel catfish (Ictalurus punctatus), which have multiplied dramatically since around 2000 in Lake Kasumigaura, Japan, on native fish and shrimp and the commercial fishery using fishery-independent, quantitative long-term monitoring data (1993 2007). 2. Temporal changes in abundance of 17 native fish species and one native shrimp species were analysed, and their sensitivity was evaluated, measured as change in relative abundance to the increase in I. punctatus abundance, was evaluated. A trait analysis of 18 species was performed in an attempt to investigate biological traits related to a negative sensitivity to I. punctatus invasion. 3. After controlling for the effect of trophic status (total nitrogen and total phosphorus), nine of the 18 native species declined significantly through time and showed negative sensitivity to the increase in I. punctatus abundance; these included all four species used as raw materials for Japanese traditional processed foods. The trait-based analysis also revealed that benthic species and/or the species with a narrow diet range have decreased in abundance with increasing I. punctatus abundance. This suggests that competition for food, rather than predation by I. punctatus, is an important mechanism that results in a negative impact on native species. 4. This study suggests that I. punctatus invasion may change the native community composition and negatively influence commercially important species, leading to a reduction in the provision of ecosystem goods. Copyright (C) 2011 John Wiley & Sons, Ltd.