Long-term effects of local hydrology and regional climate on American shad and striped bass in the Hudson River estuary

It has been hypothesized that climate change is an underlying factor in determining fish abundances in the Hudson River estuary (HRE).  To study the effects of hydrology and climate on the HRE fish assemblage, we applied multivariate statistical methods to 20 species-life history stages collected from 1974 to 2005. Our results confirm that changes in the HRE fish assemblage are correlated with local hydrology (freshwater flow and water temperature) and regional climate (Atlantic Multidecadal Oscillation or AMO and North Atlantic Oscillation or NAO).  We found that abundances of striped bass larval stages are positively correlated with high freshwater flows and juvenile shad abundances are negatively correlated with the AMO. Because the AMO is based upon North Atlantic sea surface temperatures (SST) values, our results suggest that increases in juvenile shad abundances are negatively correlated with North Atlantic SSTs. A cross-correlation analysis showed a significant negative correlation between the AMO and HRE juvenile shad abundances at a 3-year positive lag which may reveal the mechanistic link between ocean climate and HRE juvenile American shad populations. Our findings suggest that climate-related variability affects HRE juvenile shad abundances and current management strategies for this declining species should include the implications of climate change.