Invasive brown trout Salmo trutta induce differential growth strategies in the native snow trout Schizothorax richardsonii of Himalaya: Are natives in unaltered rivers better at picking the gauntlet of invasion?

다국어 초록 (Multilingual Abstract)

Brown trout Salmo trutta is a potent global invader and its establishments have progressively altered physiologies, life‐histories and niche‐availabilities for native fish species. River impoundments further escalate its invasion potential. The Himalayan rivers however, stay uncharted for the effects of brown trout interactions with the native fish fauna. Snow trout Schizothorax richardsonii a Himalayan cold‐water native, concerningly overlaps its range with brown trout. To understand its responses to invasion pressures, we investigated brown trout effects on the age and growth of snow trout populations in three rivers with varying levels of perturbation: (a) a dammed and (b) an undammed river with the invasive brown trout in comparison to (c) an undammed river without invasion pressures. We found sympatric snow trout in the undammed river to respond to brown trout invasion with fast life history responses, showing an early age‐at‐maturity (A50 = 1.2 years) and fast growth with a higher growth constant (K = 0.40 yr−1) and specific rate of linear growth across life. On the contrary, sympatric snow trout in the dammed river showed an explicitly slow life‐history by maturing at a higher age (A50 = 2.9 years) and a slow growth, with a lower growth constant (K = 0.26 yr−1) and specific linear growth rates. Our findings suggest that, the snow trout appear to present stronger response to brown trout invasions when the river is unaltered and free from hydropower operations and damming. Further research is strongly warranted from other high‐altitude Himalayan basins to delineate the variation in growth strategies exhibited by snow trout in sympatry with the invasives.