UW Aquatic & Fishery Sciences Quantitative Seminar

Jon Ruem

UW-School of Aquatic and Fishery Sciences

Evaluating Intra and interannual responses of Pacific herring and surf smelt to environmental forcing in the Skagit River estuary (Washington, USA) using two-stage generalized additive models


Forage fish are key components of coastal marine food webs and play a major role in the Puget Sound ecosystem by linking zooplankton to predators higher in the food chain. Given their importance, evaluating how environmental variability influences the distribution and abundance of forage fish is critical for developing an understanding of system-level responses to future climate scenarios. Here, we evaluated intra and interannual patterns of abundance of Pacific herring and surf smelt in the Skagit River estuary using a nine year time series spanning 2001-2009. Specifically, we evaluated the response of forage fish to variation in water temperature and salinity and examined relationships between interannual abundance patterns and regional environmental drivers (cumulative river discharge, coastal upwelling indices, sea surface temperature). Our findings indicate that local water conditions explain only a small fraction (<3%) of the total variability in fish abundances. In contrast, interannual differences, or year effects, were the primary source of variation. Moderate correlations were observed between adult surf smelt and cumulative spring river discharge (Feb – May) and juvenile Pacific herring and surf smelt were correlated with cumulative spring upwelling. Furthermore, strong correlations between our juvenile Pacific herring index with a similar index for populations in the Strait of Georgia suggest that regional climate forcing may synchronize herring recruitment throughout the Salish Sea. Identifying the primary sources of variability in abundance patterns is a first step towards developing mechanistic models that link Puget Sound’s forage fish populations to climate and our work highlights areas of future research.

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