Epsilon Archive for Student Projects

Abstract

Eurasian minnow (Phoxinus phoxinus) are spreading into brown trout (Salmo trutta) lakes in the Swedish Arctic due to bait releases from anglers or possibly due to habitat improvement induced by climate change. Previous studies have shown that introduced minnow can negatively affect trout through resource and habitat competition and predation. We investigated lake-adjacent trout nursery streams in the Abisko area where minnow are colonizing lake systems. My aim was to uncover possible impacts of the newly established minnow on trout growth, age structure, condition, density, trophic position and niche width, as well as impacts on the prey community. We electrofished several lake inlets and measured weight and length of the caught trout and minnow. We also collected macroinvertebrates. I analyzed trout otoliths for age estimation and conducted a stable isotope analysis to assess trout and minnow diets. I found that trout in stretches where minnow were present had a shorter length-at-age at 3+ and possibly 4+ than trout in allopatry, suggesting slower growth. I found multiple tendencies that hint at further influences of minnow on trout, e.g. differing age structures between stretches with and without minnow, which indicate that trout in sympatry leave their nursery streams earlier. There also seems to be a tendency for fewer rare macrobenthos taxa in the presence of minnow, which suggests an influence of minnow on trout prey. I could not confirm an influence of minnow presence on trout condition, density or prey size, possibly due to the small sample size (n = 7). This thesis can serve as the foundation for a long-term study with more investigated streams that could reveal if minnow have a more severe impact on trout in this area.