Dra. Sobenes-Vennekool, Catterina

The adverse impacts of invasive salmonids on native galaxiids are well documented at the population level in the freshwater ecosystems of the Southern Hemisphere. However, the mechanism underlying these interactions and sub-lethal effects of salmonids on native galaxiids at the individual level remain poorly understood. In this study, a series of controlled experiments was conducted to assess sub-lethal interactions between invasive brown trout (Salmo trutta) and the native Galaxias platei at an individual level. The microhabitat preferences of G. platei were evaluated in response to potential competition with juvenile brown trout and predation risk from piscivorous adults. In addition, the swimming capacity of G. platei was assessed to determine their ability to escape predation. The results show that at increasing densities of juvenile brown trout, G. platei fails to increase refuge use and are more frequently observed in open habitats. Furthermore, G. platei juveniles exhibit significantly lower swimming capacity compared to brown trout. In the presence of predatory trout, G. platei does not display a heightened preference for refuge habitats. These findings suggest that the behavioral response of G. platei could be insufficient to reduce competition and predation risks posed by brown trout and potentially other salmonids.

The introduction of predatory salmonids such as rainbow trout Oncorhynchus mykiss Walbaum 1792, and brown trout Salmo trutta Linnaeus 1758, has been responsible for declining populations of native galaxiids in the Southern Hemisphere. The empirical evidence of mechanisms of this decline are, however, scarce. Currently, trout are the most common species in Chilean Patagonia. Galaxias platei Steindachner 1898 is the most widely distributed native species in Patagonia and can still be found in lakes that are not invaded by salmonids. We studied the trophic ecology of the two most common trout species (rainbow and brown) as well as G. platei in invaded and non-invaded lakes by analysing their diet and isotopic composition of their muscle tissues (carbon and nitrogen). The results indicated that the presence of trout delayed piscivory in G. platei and led to a slower ontogenetic scaling and lower trophic level. In addition, juveniles of G. platei tended to expand their trophic niche toward allochthonous prey in salmonid-invaded lakes. Trout showed high levels of piscivory, preying mainly on G. platei. The protection of the remaining salmonid-free lakes appears to be a crucial measure needed for the conservation of G. platei.