Movement and early survival of age-0 brown trout

International audienceComplementary data on survival and movement are often missing for early life stages that are logistically challenging to track. Previous studies observed significant declines in the density of age-0 brown trout between summer and autumn in tributaries of Lake Geneva, but the cause of these declines was unknown. We hypothesised that mortality, dispersal within tributaries, early emigration to the lake or a combination of these factors was driving these seasonal declines. To evaluate these hypotheses, we used a combination of electrofishing and PIT-tag mark-recaptures from stationary and portable antennae to quantify summer-to-autumn variation in the abundance, dispersal and emigration of age-0 brown trout. Mortality was the primary cause of the reduction in abundance between summer and autumn. A small proportion (mean=0.10) of age-0 trout emigrated to Lake Geneva between July and mid-October, while the movement of trout within the study streams was minimal. True survival estimates for this same time period were relatively low at all but one site (mean=0.63). The seasonal resolution of survival estimates, paired with environmental data, allowed us to develop additional hypotheses on what factors were affecting survival. Understanding animal movement at early life stages can elucidate important aspects of population ecology while concomitantly improving the reliability of demographic data