Non-native minnows cause much larger negative effects than trout on littoral macroinvertebrates of high mountain lakes

Osorio, Víctor; Puig, Mariàngels; Buchaca, Teresa; Sabas, Ibor; Miró, Alexandre; Lucati, Federica; Suh, Jongmo; Pou-Rovira, Quim; Ventura, Marc. Biological Conservation 272 : 109637 (2022)  DIGITAL CSIC

Despite being naturally fishless, the widespread introduction of trout and minnows is threatening the conservation of high mountain lakes all over the world. Previous studies have reported that amphibians quickly disappear after trout introduction, followed by many conspicuous invertebrates. Here, we have studied the effects of minnows versus trout on the littoral macroinvertebrate community of 54 high mountain lakes from the Pyrenees, covering a gradient of environmental characteristics. The relative importance of fish compared to other variables in explaining macroinvertebrate communities was assessed using distance-based redundancy analysis (dbRDA) and multivariate regression tree (MRT) to find the main environmental thresholds. Both dbRDA and MRT approaches revealed that minnow density was the most important variable negatively determining community structure, followed by aquatic macrophytes, which increased taxa richness. The occurrence and abundance of relevant taxa was analysed in relation to fish densities and other environmental factors using binomial and gamma generalized linear models (GLM). GLM suggested that trout had an impact on the distribution of swimmer taxa and caused declines in the abundance of conspicuous clinger and burrower taxa. Minnows restricted the occurrence of more taxa than trout and negatively affected a wide variety of body sizes and functional groups. Indeed, we found that minnows were responsible for a dramatic biodiversity loss in the littoral macroinvertebrate community. The fast spread of minnows in high mountain areas is of great concern for the conservation of lake macroinvertebrates. Urgent measures to stop minnow introductions are strongly recommended.