2011: Multiscale influence of climate on estuarine forage fish: the role of coastal upwelling, river discharge and local water temperature and salinities. MEPS 425: 203–215.
Jonathan Reum, Tim Essington, Correigh Greene, Casey Rice, Kurt Fresh
We examined how local– and regional-scale environmental drivers affect patterns of abundance and recruitment in 2 abundant and ecologically significant forage fishes (Pacific herring Clupea pallasi and surf smelt Hypomesus pretiosus) in the Skagit River estuary (Puget Sound, Washington, USA). We identified associations between survey catch rates and environmental conditions at two scales: within-season distributional shifts in response to local environmental conditions, and interannual patterns of relative year class strength related to both local– and regional-scale drivers. Using monthly data that spanned a 9 yr period, we found that a small proportion (<2%) of the total deviance in catch rates for both species was related to within-estuary variation in surface water temperature and salinity but that a larger fraction (7 and 12% for Pacific herring and surf smelt, respectively) was explained by interannual variation in recruitment strength. Annual abundance indices for both species were uncorrelated with cumulative river discharge and regional sea surface temperature but positively correlated with an index of cumulative coastal upwelling, suggesting a linkage between regional-scale environmental conditions and age-0 recruitment. Moreover, our annual age-0 Pacific herring time series was positively correlated with a similar time series from the Strait of Georgia (~100 km north), further suggesting that age-0 recruitment in these populations is synchronized by regional upwelling as opposed to estuary-specific environmental forcing related to river flows. The present study isolates a potential key process governing age-0 forage fish abundance in this system and highlights the importance of simultaneously evaluating patterns of variability across multiple spatiotemporal scales in order to identify the primary pathways through which climate may impact estuarine populations.