Evidence of exotic trout mediated minnow invasion in Pyrenean high mountain lakes

Although high mountain lakes are naturally fishless, there have been numerous trout introductions to such ecosystems in many areas of the world with negative ecological consequences. In recent decades other fishes, such as minnows, have been introduced to some mountain areas, including the Pyrenees. These introductions may cause further ecological problems, since minnows also occupy the top of the food chain, and are difficult to manage since such introductions occur without permission from the authorities. In this study we have analyzed the process of minnow introductions in all high mountain lakes of the southern slope of the Pyrenees to find out which particular factors best explained their present distribution and to evaluate which management measures have been most effective for stopping introductions. We found 27 % of the lakes had minnows (Phoxinus sp.) present, 52 % had trout and 47 % were fishless. Trout presence was the most significant variable explaining 27 % of deviance of minnow presence data in a generalized additive model. Recreational fishing using minnows as live bait is likely responsible for these introductions. Minnow introductions are therefore mediated by a preceding invasive species and facilitated by human activity. We also compared the number of minnow introductions in non-fishing areas of National Parks with other areas where managed fishing takes place. We found that the number of lakes with minnow introductions was increasing in all areas except those where fishing was prohibited, indicating that prohibiting fishing is an effective management practice for stopping minnow introductions.Peer reviewe