Shifts in spawning phenology may impact the early life stages of small pelagic fishes, affecting their first-year survival and recruitment. In Prince William Sound, Pacific herring is a key forage species that once supported commercial and subsistence fisheries for many decades, but collapsed in 1993 and has yet to recover. Starting in 1980, spawn timing shifted earlier by approximately 2-4 wk over a 27 yr period, then abruptly shifted later by approximately 3 wk over the next 7 yr. We quantified the influence of 15 environmental and population-level covariates on these spawn timing shifts using generalized linear models. Earlier spawn timing was associated with higher biomass in the eastern sound and older mean age in the western sound. Across the entire sound, earlier spawning was associated with weaker downwelling, weaker meridional winds, and the positive phase of the Pacific-North American teleconnection pattern, which is characterized by warmer North Pacific waters. These results are a critical first step towards assessing how changes in spawning phenology impact first-year survival of herring offspring and potentially contribute to persistent poor recruitment that has inhibited the recovery of the Prince William Sound population.