| Summary: | Spatial and temporal synchrony in abundance or survival trends can be indicative of whether populations are affected by common environmental drivers. In Atlantic salmon ( Salmo salar L.), return rates to natal rivers have generally been assumed to be affected primarily by shared oceanic conditions, leading to spatially synchronous trends in mortality. Here, we investigate the existence of parallel trends in salmon sea survival, using data on migrating smolts and returning adults from seven Canadian populations presumed to share feeding grounds. We analyse sea survival, using a Bayesian change-point model capable of detecting non-stationarity in time series data. Our results indicate that while salmon have experienced broadly comparable patterns in survival, finer-scale temporal shifts are not synchronous among populations. Our findings are not consistent with the hypothesis that salmon populations consistently share the same mortality-related stressors in the marine environment. Although populations may have shared greater synchrony in survival patterns in the past, this synchrony may be breaking down. It may be prudent to direct greater attention to smaller-scale regional and population-level correlates of survival In each river-specific data set, there are the following variables: year river_name sw_dominance: the population is either dominated by 1SW (value '1') or 2SW fish ('2') logsmolts: the recorded number of smolts in log-scale for each year logsmolts_est: the estimated true smolt abundance (the posterior median obtained by Pardo et al., 2021) for each year logSW1: the recorded number of returning 1SW fish in log-scale logSW2: the recorded number of returning 2SW fish in log-scale logSW1_cv: the estimated measurement error in logSW1 logSW2_cv: the estimated measurement error in logSW2 For three rivers, there was one or two missing years within their time series. For those years, there had been no smolt count due to too much water flow. In addition, in some years for 1SW-dominated populations, estimates ...
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