Importance of Winter Upwelling to California Current Ecosystem Dynamics

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Climate variability on multiple temporal scales is increasingly recognized as a major factor influencing the structure, functioning, and productivity of the California Current Ecosystem. Yet despite long-term and integrative studies, a detailed understanding of climatic impacts is still lacking, compromising our abilities to interpret ecosystem variability over time and use that information to assess important concepts such as ecosystem health and resilience. Recent attempts to better establish the effects of climate have emphasized the relationship of reproductive and growth strategies of fish and seabirds to ecosystem phenology, particularly the timing of what is known as the "spring transition" from wintertime to spring upwelling conditions. However, there no clear definition of the spring transition has yet been established, and estimated spring transition dates do not adequately predict ecosystem productivity. Moreover, an increasing body of evidence suggests that ecosystem productivity is most sensitive to wintertime ocean variability prior to the traditional spring transition date. To address the importance of wintertime ocean conditions, a unique assemblage of rockfish and seabird time series relating to growth and reproductive success will be collated and analyzed with respect to environmental variability. All rockfish and seabird time series are multidecadal in length, annually resolved, and provide a view from the top by integrating ecosystem productivity after it has cascaded up through multiple lower trophic levels. This multi-species approach is particularly powerful considering that rockfish and seabird data independently reinforce one another. Pilot work shows that rockfish and seabird time series are strongly interrelated, and that these relationships are driven by shared sensitivities to wintertime ocean conditions, particularly February upwelling. Thus, the objectives of this study are to i) quantify the interrelationships among rockfish and seabird growth and reproduction time series, ii) identify the climatic variables, with an emphasis on the winter months, that correspond with covariability in rockfish and seabirds, and iii) evaluate the extent to which the abundance, distribution, and spatial organization of euphausiid crustaceans, a key prey item in the ecosystem, covary with seabirds, rockfish, and wintertime ocean conditions.This study will establish the times of year under which climate exerts the greatest influence on key upper-trophic level species, and provide leading biological and physical indicators of ecosystem productivity in the California Current Ecosystem. These biophysical indicators will be made available for integration into fisheries stock assessments and will also be of use for forecasting fisheries responses under various climatic scenarios. This information will also provide input to the California Current Integrated Ecosystem Assessment under development by NOAA-NMFS and others. In addition, the project will provide postdoctoral training in physical oceanography and undergraduate training in rockfish otolith growth-increment analysis.