Impact of Climate Variability on the Spawning Migrations of American Shad in the Connecticut River – a Multidecadal View

American shad, an anadromous species, exhibits latitudinal variation in parity. Temperatures in the south promote semelparity by favoring survival of first-year fish and mortality of adults; whereas more variable temperatures in the north promote iteroparity. Two in-river habitat variables – temperature and flow rates – have been associated with recruitment, indicating that temperature may also be a driver of population dynamics in general. The objective of this study was to determine if climate variability is affecting the spawning run of American shad in the Connecticut River from 1974 to 2015. Correlation and regression analysis test for a trend between temperature and flow habitat variables and proxies of spawning run timing. A statistical model examines how temperature and flow rates interact with stock size, lagged recruitment, and percentage of repeat spawners. Preliminary analyses reveal that mean temperatures have been increasing in the Connecticut River over the last few decades, with increasing fluctuations in shad between years. Shad have exhibited earlier spawning migrations as temperatures increase, which may be adaptive if it limits the impact of environmental variation on reproductive success; however, the declining numbers of repeat spawners suggest other dynamics that may reduce population stability.