Spatial variation buffers temporal fluctuations in early juvenile survival for an endangered Pacific salmon

Abstract

Summary1. Spatial, phenotypic and genetic diversity at relatively small scales can buffer species against large-scale processes such as climate change that tend to synchronize populations and increase temporal variability in overall abundance or production. This portfolio effect generally results in improved biological and economic outcomes for managed species. Previous evidence for the portfolio effect in salmonids has arisen from examinations of time series of adult abundance, but we lack evidence of spatial buffering of temporal variability in demographic rates such as survival of juveniles during their first year of life. 2. We therefore use density-dependent population models with multiple random effects to represent synchronous (similar among populations) and asynchronous (different among populations) temporal variability as well as spatial variability in survival. These are fitted to 25 years of survey data for breeding adults and surviving juveniles from 15 demographically distinct populations of Chinook salmon (Oncorhynchus tshawytscha) within a single metapopulation in the Snake River in Idaho, USA. 3. Model selection identifies the most support for the model that included both synchronous and asynchronous temporal variability, in addition to spatial variability. Asynchronous variability (log-SD = 0Á55) is approximately equal in magnitude to synchronous temporal variability (log-SD = 0Á67), but much lower than spatial variability (log-SD = 1Á11). We also show that the pairwise correlation coefficient, a common measure of population synchrony, is approximated by the estimated ratio of shared and total variance, where both approaches yield a synchrony estimate of 0Á59. We therefore find evidence for spatial buffering of temporal variability in early juvenile survival, although between-population variability that persists over time is also large. 4. We conclude that spatial variation decreases interannual changes in overall juvenile production, which suggests that conservation and restoration of spatial diversity will improve population persistence for this metapopulation. However, the exact magnitude of spatial buffering depends upon demographic parameters such as adult survival that may vary among populations and is proposed as an area of future research using hierarchical life cycle models. We recommend that future sampling of this metapopulation employ a repeated-measure sampling design to improve estimation of early juvenile carrying capacity.

Setting spatial conservation priorities despite incomplete data for characterizing metapopulations

“…Our estimate of metapopulation structure for the Snake River spring/summer Chinook salmon evolutionarily significant unit (ESU), based on all available information, was congruent with previous findings (ICTRT , , Thorson et al. , Jorgensen et al. ).…”

Timing matters: species‐specific interactions between spawning time, substrate quality, and recruitment success in three salmonid species

“…A high microscale variability of interstitial water conditions during egg development was previously detected (Malcolm et al 2009; Sternecker et al 2013b) and seems to be characteristic of the hyporheic zone of most stream ecosystems (Braun et al 2012). Such variation at small spatial scales was recently described to buffer temporal fluctuations in early juvenile survival in Pacific Chinook salmon (Thorson et al 2014). Substratum depth in our study was limited to 150 mm, hence deeper zones with a potential flow-through of oxygen rich ground water was not considered resulting in a possible underestimation of hatching success (Peterson and Quinn 1996b).…”

“…Such an adverse synergistic effect of stream substrate degradation and increased water temperature on salmonids was detected in our study and found to be species-specific. It is likely to be driven by variable and scale-dependent physicochemical and genetic impacts (Sternecker et al 2013b; Thorson et al 2014). Consequently, there is no general solution for the support of declining salmonid populations, as restoration concepts have to consider specific conditions of the river (stretch) to be restored as well as specific demands of the target species.…”

Science Advancements Key to Increasing Management Value of Life Stage Monitoring Networks for Endangered Sacramento River Winter-Run Chinook Salmon in California

“…Variability in juvenile size, timing and habitat use during downstream migration to the ocean ensures that some component of the population in dynamic environments experiences favorable riverine, estuarine, and ocean conditions (Beechie et al 2006;Sattherthwaite et al 2014). The extent to which fish have access to spatially diverse habitats influences their rate of growth, movement, and phenotypic diversity, and has been shown to stabilize inter-annual variation in juvenile production (Thorson et al 2014 (Miller et al 2010;Sturrock et al 2015). Understanding the survival of SRWRC rearing in the Delta was identified as one of the largest empirical data gaps in the development of the NMFS SRWRC life-cycle model (Hendrix et al 2014;Perry et al 2016).…”