Reconstructing the Migratory Behavior and Long-Term Survivorship of Juvenile Chinook Salmon under Contrasting Hydrologic Regimes

Abstract

The loss of genetic and life history diversity has been documented across many taxonomic groups, and is considered a leading cause of increased extinction risk. Juvenile salmon leave their natal rivers at different sizes, ages and times of the year, and it is thought that this life history variation contributes to their population sustainability, and is thus central to many recovery efforts. However, in order to preserve and restore diversity in life history traits, it is necessary to first understand how environmental factors affect their expression and success. We used otolith 87Sr/86Sr in adult Chinook salmon (Oncorhynchus tshawytcha) returning to the Stanislaus River in the California Central Valley (USA) to reconstruct the sizes at which they outmigrated as juveniles in a wetter (2000) and drier (2003) year. We compared rotary screw trap-derived estimates of outmigrant timing, abundance and size with those reconstructed in the adults from the same cohort. This allowed us to estimate the relative survival and contribution of migratory phenotypes (fry, parr, smolts) to the adult spawning population under different flow regimes. Juvenile abundance and outmigration behavior varied with hydroclimatic regime, while downstream survival appeared to be driven by size- and time-selective mortality. Although fry survival is generally assumed to be negligible in this system, >20% of the adult spawners from outmigration year 2000 had outmigrated as fry. In both years, all three phenotypes contributed to the spawning population, however their relative proportions differed, reflecting greater fry contributions in the wetter year (23% vs. 10%) and greater smolt contributions in the drier year (13% vs. 44%). These data demonstrate that the expression and success of migratory phenotypes vary with hydrologic regime, emphasizing the importance of maintaining diversity in a changing climate.

Survival of Juvenile Fall‐Run Chinook Salmon through the San Joaquin River Delta, California, 2010–2015

“…; Carlson and Satterthwaite ; Sturrock et al. ). A priority on habitat quality within the Delta, combined with efforts to improve survival through all portions of the salmon life history, is likely to be required if this population is to persist.…”

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

“…To quantify survival and relative contribution of different juvenile rearing strategies to population productivity, an annual time-series metric of juvenile life-history diversity, migration, and habitat can be developed by collecting and analyzing the otoliths of SRWRC adults from the LSNFH broodstock and in-river spawners annually. These techniques are well established and widely used (Barnett-Johnson et al 2005Sturrock et al 2015;; Figure 13). The chemical composition and the banding patterns in otoliths record the migration history (duration of time in different habitats) and condition (growth) age-structure diversity in SRWRC through harvest management.…”

“…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).…”

“…These predictions could be tested, and the model refined, by analyzing otoliths of juveniles collected at Sacramento, CA or Chipps Island to reveal the duration of time spent rearing in habitats in these different geographic regions. In addition, comparing the abundance and size distributions of juvenile SRWRC that entering the Delta to their representation in the adult returns yields a survival estimate for fry-sized SRWRC that reared in the Delta (Sturrock et al 2015;reviewed in Perry et al 2016). Otoliths have been collected from SRWRC carcasses and broodstock at the LSNFH intermittently.…”

“…• Chemical analyses used to reconstruct migration patterns (Sturrock et al, 2015), population of origin (Barnett-Johnson et al 2008;, and diet (Weber et al 2002) • Alaska hatcheries "thermally mark" fish by varying temperatures in unique patterns visibly recorded in otoliths (Scott et al 2001) • Freshwater growth rates linked to higher ocean survival (Woodson et al 2013) by battery life, tags can possibly be recovered later in downstream monitoring surveys, or upon return in adult carcass surveys, or at the LSNFH. Handheld PIT-tag readers can be used at any monitoring location where fish are handled to identify the unique code of each PIT tag.…”