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Better fisheries management is often given as one justification for research on improving forecasts of fish survival. However, the value gained from expected improvements in forecast skill in terms of achieving management goals is rarely quantified as part of research objectives. Using Monte Carlo simulations of population dynamics, we assessed the effect of forecast skill under two strategies for managing Oregon coast natural (OCN) coho salmon ( Oncorhynchus kisutch). The first, or status quo, strategy is currently being used to rebuild threatened OCN coho populations. This strategy determines harvest based on both a forecasted marine survival rate and parental spawner abundance. The second strategy relies on a forecast of preharvest adult abundance to achieve a constant spawner escapement target. Performance of the status quo strategy was largely insensitive to forecast skill, while the second strategy showed sensitivity that varied with escapement target and specific performance metric. The results imply that effort towards improving forecasts is not justifiable solely on the basis of improved management under the status quo strategy, though it may be were the management strategy altered. [ABSTRACT FROM AUTHOR]

Generalized additive models (GAMs) were used to investigate the relationships between annual recruitment of natural coho salmon ( Oncorhynchus kisutch) from Oregon coastal rivers and indices of the physical ocean environment. Nine indices were examined, ranging from large-scale ocean indicators, e.g., Pacific Decadal Oscillation (PDO), to indicators of the local ecosystem (e.g., coastal water temperature near Charleston, OR). Generalized additive models with two and three predictor variables were evaluated using a set of performance metrics aimed at quantifying model skill in short-term (approximately 1 yr) forecasting. High explanatory power and promising forecast skill resulted when the spring/summer PDO averaged over the 4 yr prior to the return year was used to explain a low-frequency (multi-year) pattern in recruitment and one or two additional variables accounted for year-to-year deviations from the low-frequency pattern. More variance was explained when averaging the predictions from a set of models (i.e., taking the ensemble mean) than by any single model. Making multiple forecasts from a set of models also provided a range of possible outcomes that reflected, to some degree, the uncertainty in our understanding of how salmon productivity is driven by physical ocean conditions. [ABSTRACT FROM AUTHOR]

The ocean survival of coho salmon ( Oncorhyncus kisutch) off the Pacific Northwest coast has been related to oceanographic conditions regulating lower trophic level production during their first year at sea. Coastal upwelling is recognized as the primary driver of seasonal plankton production but as a single index upwelling intensity has been an inconsistent predictor of coho salmon survival. Our goal was to develop a model of upwelling-driven meso-zooplankton production for the Oregon shelf ecosystem that was more immediately linked to the feeding conditions experienced by juvenile salmon than a purely physical index. The model consisted of a medium-complexity plankton model linked to a simple one-dimensional, cross-shelf upwelling model. The plankton model described the dynamics of nitrate, ammonium, small and large phytoplankton, meso-zooplankton (copepods), and detritus. The model was run from 1996 to 2007 and evaluated on an interannual scale against time-series observations of copepod biomass. The model's ability to capture observed interannual variability improved substantially when the copepod community size distribution was taken into account each season. The meso-zooplankton production index was significantly correlated with the ocean survival of hatchery coho salmon from the Oregon production area, although the coastal upwelling index that drove the model was not itself correlated with survival. Meso-zooplankton production within the summer quarter (July-September) was more strongly correlated with coho survival than was meso-zooplankton production in the spring quarter (April-June). [ABSTRACT FROM AUTHOR]

Simple plankton models serve as useful platforms for testing our understanding of the mechanisms underlying ecosystem dynamics. A simple, one-dimensional plankton model was developed to describe the dynamics of nitrate, ammonium, two phytoplankton size-classes, meso-zooplankton, and detritus in the Oregon upwelling ecosystem. Computational simplicity was maintained by linking the biological model to a one-dimensional, cross-shelf physical model driven by the daily coastal upwelling index. The model sacrificed resolution of regional-scale and along-shore (north to south) processes and assumed that seasonal productivity is primarily driven by local cross-shelf Ekman transport of surface waters and upwelling of nutrient-rich water from depth. Our goals were to see how well a simple plankton model could capture the general temporal and spatial dynamics of the system, test system sensitivity to alternate parameter set values, and observe system response to the effective scale of potential retention mechanisms. Model performance across the central Oregon shelf was evaluated against two years (2000–2001) of chlorophyll and copepod time-series observations. While the modeled meso-zooplankton biomass was close in scale to the observed copepod biomass, phytoplankton was overestimated relative to that inferred from the observed surface chlorophyll concentration. Inshore, the system was most sensitive to the nutrient uptake kinetics of diatom-size phytoplankton and to the functional grazing response of meso-zooplankton. Meso-zooplankton was more sensitive to alternate parameter values than was phytoplankton. Reduction of meso-zooplankton cross-shelf advection rates (crudely representing behavioral retention mechanisms) reduced the scale of model error relative to the observed seasonal mean inshore copepod biomass but had little effect of the modeled meso-zooplankton biomass offshore nor upon phytoplankton biomass across the entire shelf. [Copyright &y& Elsevier]

Both simple and more complex lower trophic ecosystem models were applied to the near shore pelagic zone of the California Current System. The ecosystem models were a simple nitrogen–phytoplankton–zooplankton (NPZ) model derived from that of Edwards et al. (J. Mar. Res. 58, 37–60, 2000), and a modified version of the more complex PICES North Pacific Ecosystem Model for Understanding Regional Oceanography (NEMURO), which includes both nitrogen and silicate cycles, as well as multiple phytoplankton and zooplankton components. These models were framed within two simplified physics models, similar to those constructed by Newberger et al. (J. Geophys. Res. 108 (3), 3061, doi:10. 1029/2001JC001182, 2003). The first physics model was a zero-dimensional closed system, used for structural analysis of the biological models. The second was a one-dimensional (horizontal, with no vertical structure) cross-shelf model of the mixed layer, used to examine the biological response to upwelling. The predictions of the two biological models within the one-dimensional physical framework were compared with observed nutrients, chlorophyll, and zooplankton on the Newport Hydrographic Line. Equilibrium behavior of the zero-dimensional models was similar to that in previous studies; differences between the models resulted primarily from differences in the density dependence of mortality. Both models were found to be highly sensitive to the same four parameters: source nitrate concentration, maximum grazing rate, zooplankton Ivlev constant, and zooplankton mortality rate. In the cross-shelf case, both biological models had a similar timing of phytoplankton response to upwelling, but maximum phytoplankton concentration and zooplankton dynamics differed, with the simpler NPZ model resulting in lower dissolved nutrients but higher plankton densities than the modified NEMURO model. While the modified NEMURO model provided a slightly better overall fit to observations, neither model was able to fully capture observed phytoplankton and zooplankton dynamics. [Copyright &y& Elsevier]

Examines the criteria for expansion of conservation of Pacific salmon stocks in the United States. Types of extinction risk; Impact of prioritization process on evolutionarily significant units of salmon; Kinds of population size criteria of the fish.

• Predictive skill in climate – salmon relationships is often ephemeral. • Failures are common when traditional regressions are applied to complex systems. • Interactions among climate, ecosystems, and populations make forecasts uncertain. • Salmon management policies need to be robust to forecast error and uncertainty. The influence of climate on marine populations is important for predicting stock abundance of marine fishes, and has led to increasing interest in environment-based forecasts (EBFs) for harvest management. While some climate indices have proven useful for explaining fluctuations in Pacific salmon stock abundance, there have also been sudden failures of EBF models. I analyzed temporal patterns in prediction skill for a variety of climate and ecosystem indicators as predictors of marine survival for a coastal coho salmon stock by computing prediction skill for 29 climate and ecosystem indices across multiple time scales to explore patterns of skill across time. Results demonstrate that predictive skill of EBF models is often ephemeral, arising and falling suddenly across time. This behavior can be explained both on a statistical basis and as a consequence of complex interactions between climate, ecosystems, and populations involving both climate regime shifts and ecosystem phase transitions. Forecast failures are problematic for traditional forecast-dependent harvest management approaches. Solutions for this problem may include improved forecast models and improved climate and ecosystem indicators, but developing management systems that are robust to forecast uncertainty would provide a more reliable response to expected rapid ecosystem changes in response to climate. [ABSTRACT FROM AUTHOR]

Many ecosystems have been dramatically affected by non-native species, but not all such species have strong deleterious effects. American shad, Alosa sapidissima, a fish species native to the Atlantic coast of North America, was transplanted to the Pacific coast in the late nineteenth century and quickly colonized many US rivers. Their increased abundance in the Columbia River coincided with declines in native anadromous Pacific salmon and trout, and adult American shad now greatly outnumber returning salmonids. This paper reviews evidence for possible ecological interactions between salmon and American shad across their life histories and habitats. Despite the great abundance of American shad and their apparent overlap in use of Columbia River mainstem habitats, harmful effects on salmon are neither clear from empirical studies nor from ecological principles. Rather, the life histories and habitat use patterns tend to separate spawning adult salmon and their offspring from American shad in space and time. Currently available evidence indicates that this separation results in weak, neutral, uncertain, or offsetting effects on salmon (i.e., a mix of positive and negative interactions). Given the limited research on shad in Pacific ecosystems, several lines of investigation are warranted to advance understanding of their ecology and scope for interactions with native fishes and to support a clearer scientific basis for management decisions regarding American shad. [ABSTRACT FROM AUTHOR]

Pathways linking climate to population dynamics of higher-trophic-level fish species such as Pacific salmon often involve a hierarchy in which regional-scale physical and biological processes mediate the effects of large-scale climate variability. We used probabilistic networks to investigate 17 potential ecological pathways linking climate to Oregon coho salmon ( Oncorhynchus kisutch) recruitment. We found that pathways originating with the Pacific Decadal Oscillation were the most influential on recruitment, with the net effect being two to four times greater than for pathways originating with the North Pacific Gyre Oscillation or the Oceanic Niño Index. Among all environmental variables, sea surface temperature and an index of juvenile salmon prey biomass had the greatest effects on recruitment, with a 76% chance of recruitment being equal to or below average given that ocean temperatures were above average and a 34% chance of recruitment being below average given that prey biomass was above average. Our results provide evidence that shifts in climate patterns could strongly influence recruitment simultaneously through multiple ecological pathways and highlight the importance of quantifying cumulative effects of these pathways on higher-trophic-level species. [ABSTRACT FROM AUTHOR]

Abstract: The Northern California Current (NCC) is a seasonally productive and open ecosystem. It is home to both a diverse endemic community and to seasonally transient species. Productivity and food web structure vary seasonally, interannually, and decadally due to variability in coastal upwelling, climate-scale physical processes, and the migratory species entering the system. The composition of the pelagic community varies between years, including changes to mid-trophic level groups that represent alternate energy-transfer pathways between lower and upper trophic levels (forage fishes, euphausiids, jellyfish). Multiple data sets, including annual spring and summer mesoscale surveys of the zooplankton, pelagic fish, and seabird communities, were used to infer NCC trophic network arrangements and develop end-to-end models for each of the 2003–2007 upwelling seasons. Each model was used to quantify the interannual variability in energy-transfer efficiency from bottom to top trophic levels. When each model was driven under an identical nutrient input rate, substantial differences in the energy available to each functional group were evident. Scenario analyses were used to examine the roles of forage fishes, euphausiids, and jellyfish (small gelatinous zooplankton and large carnivorous jellyfish) as alternate energy transfer pathways. Euphausiids were the more important energy transfer pathway; a large proportion of the lower trophic production consumed was transferred to higher trophic levels. In contrast, jellyfish acted as a production loss pathway; little of the production consumed was passed upwards. Analysis of the range of ecosystem states observed interannually and understanding system sensitivity to variability among key trophic groups improves our ability to predict NCC ecosystem response to short- and long-term environmental change. [Copyright &y& Elsevier]