Steelhead Oncorhynchus mykiss display a dizzying array of life history variation (including the purely resident form, rainbow trout). We developed a model for female steelhead in coastal California (close to the southern boundary of their range) in small coastal streams. We combined proximate (physiological) and ultimate (expected reproductive success) considerations to generalize the notion of a threshold size for emigration or maturity through the development of a state-dependent life history theory. The model involves strategies that depend on age, size or condition, and recent rates of change in size or condition during specific periods (decision windows) in advance of the actual smolting or spawning event. This is the first study in which such a model is fully parameterized based on data collected entirely from California steelhead populations, the majority of data coming from two watersheds the mouths of whose rivers are separated by less than 8 km along the coast of Santa Cruz County. We predicted the occurrence of resident life histories and the distribution of sizes and ages at smolting for steelhead rearing in the upstream habitats of these streams. We compared these predictions with empirical results and show that the theory can explain the observed pattern and variation.[Article] FIGURE 1.-Timeline of the model of steelhead life history. The intervals are designated according to their corresponding survival rates (s p ), as described in the appendix. 534 SATTERTHWAITE ET AL.

The match-mismatch hypothesis suggests there is an optimal window for organisms to undergo key life cycle events. Here, we test the importance of match-mismatch dynamics in the timing of salmon arrival to the ocean, relative to ecosystem phenology, for the ocean survival rates of hatchery-origin fall run Chinook salmon originating from California's Central Valley. Specifically, we considered tag recovery data for releases of coded-wire tagged fish released into the San Francisco Estuary during the years 1978 to 2010. We determined a time lag for each release relative to the local spring transition date (initiation of net upwelling). Additionally, we obtained information on fish condition and size at release, the number of fish released corresponding to distinct tag codes, and yearly stock-specific harvest rate estimates. We used generalized linear models, generalized additive models, and cross-validation to identify the best-supported models for the effects of release timing and other covariates on age-3 ocean fishery recovery rates, a proxy of ocean survival rates. Release time is a useful predictor of within-year variation in survival rates, above and beyond the effects of size at release, presence of disease, and the use of net pens, and the lag relative to spring transition was a slightly better predictor than year-day. The optimal release timing appeared to occur around the end of May, and the optimal time lag appeared to be approximately 70 to 115 d after the spring transition date. However, timing is only one of many factors that affected within-and among-year variation in survival.

We use a state dependent life history model to predict the life history strategies of female steelhead trout (Oncorhynchus mykiss) in altered environments. As a case study of a broadly applicable approach, we applied this model to the American and Mokelumne Rivers in central California, where steelhead are listed as threatened. Both rivers have been drastically altered, with highly regulated flows and translocations that may have diluted local adaptation. Nevertheless, evolutionary optimization models could successfully predict the life history displayed by fish on the American River (all anadromous, with young smolts) and on the Mokelumne River (a mix of anadromy and residency). The similar fitness of the two strategies for the Mokelumne suggested that a mixed strategy could be favored in a variable environment. We advance the management utility of this framework by explicitly modeling growth as a function of environmental conditions and using sensitivity analyses to predict likely evolutionary endpoints under changed environments. We conclude that the greatest management concern with respect to preserving anadromy is reduced survival of emigrating smolts, although large changes in freshwater survival or growth rates are potentially also important. We also demonstrate the importance of considering asymptotic size along with maximum growth rate.

Biocomplexity contributes to asynchronous population dynamics, buffering stock complexes in temporally variable environments, a phenomenon referred to as a "portfolio effect". We previously revealed a weakened but persistent portfolio effect in California's Central Valley fall-run Chinook salmon (Oncorhynchus tshawytscha), despite considerable degradation and loss of habitat. Here, we further explore the timing of changes in variability and synchrony and relate these changes to factors hypothesized to influence variability in adult abundance, including hatchery release practices and environmental variables. We found evidence for increasing synchrony among fall-run populations that coincided temporally with increased off-site hatchery releases into the estuary but not with increased North Pacific environmental variability (measured by North Pacific Gyre Oscillation), nor were common trends well explained by a suite of environmental covariates. Moreover, we did not observe a simultaneous increase in synchrony in the nearby Klamath-Trinity system, where nearly all hatchery releases are on-site. Wavelet analysis revealed that variability in production was higher and at a longer time period later in the time series, consistent with increased environmental forcing and a shift away from dynamics driven by natural spawners.Résumé : La biocomplexité participe à une dynamique asynchrone des populations, limitant les variations au sein des complexes de stocks dans les milieux variables dans le temps, un phénomène appelé « effet portefeuille ». Nous avons déjà fait état d'un effet portefeuille affaibli, mais persistant chez les saumons quinnats (Oncorhynchus tshawytscha), à montaison automnale de la vallée centrale de Californie, malgré la dégradation et la disparition considérables d'habitats. Nous examinons plus en profondeur le moment des modifications de la variabilité et de la synchronie et les relions à des facteurs présumés influencer la variabilité de l'abondance des adultes, dont les pratiques de lâcher des écloseries et des variables environnementales. Nous observons des indices d'une synchronie croissance dans les populations à montaison automnale qui coïncide dans le temps avec une augmentation des lâchers d'écloseries hors site dans l'estuaire, mais non avec une variabilité accrue du milieu nord-pacifique (mesurée par l'oscillation du tourbillon nord-pacifique); en outre, un ensemble de covariables environnementales n'explique pas bien des tendances répandues. De plus, nous n'observons pas une augmentation simultanée de la synchronie dans le système voisin de Klamath-Trinity, où presque tous les lâchers d'écloseries se font sur place. L'analyse des ondelettes révèle que la variabilité de la production est plus grande et présente une plus longue période plus tard dans la série chronologique, ce qui concorde avec un forçage environnemental accru et une dynamique de moins en moins contrôlée par les géniteurs naturels. [Traduit par la Rédaction]