Medium‐term environmental changes influence age‐specific survival estimates in a salmonid population

Human-induced environmental change is a major stressor on freshwater habitats that has resulted in the population declines of many species. Ontogenetic shifts habitat use and associated (st)age-specific requirements mean impacts stressors can influence (st)ages differently, yet relatively few studies fish populations account for their detail. We aimed to identify biotic factors affecting survival estimated six age-classes European grayling River Wylye, UK over 17-year period. used Bayesian age-structured state space model estimate cohorts between subsequent life stages (eggs age 5 adults) 16 annual transitions (2003–2004 2018–2019), whilst accounting imperfect sampling population. quantified effects seasonal water flow temperature, in-stream prey resource, potential competitors predators stages. variable selection gauge relative importance survival. Grayling abundances declined during study period (>75% all age-classes), predominately driven by loss mature adults. Changes flows negatively influenced survival: increased days summer low related decreased subadults adults, lower winter reduced recruitment juveniles from eggs. Higher macrophyte cover juvenile subadult increasing high temperature appeared detrimental Abundance brown trout (a competitor predator) did not Our results reveal implications salmonid population, where recent temperatures, below average flows, have These conditions appear be becoming more frequent persistent our river, which towards species’ southern range limit, could render vulnerable climate change. demonstrates how careful analysis long-term monitoring datasets dynamics, when combined with local expertise, realistic mitigation proposals promote wildlife persistence.