Multi-decadal shifts in the distribution and timing of Pacific herring (Clupea pallasii) spawning in Prince William Sound, Alaska

The location and timing of spawning play a critical role in pelagic fish survival during early life stages and can affect subsequent recruitment. Spawning patterns of Pacific herring (Clupea pallasii) were examined in Prince William Sound (1973–2019) where the population has failed to recover since its collapse in 1993. Abrupt shifts in spawn distribution preceded the rapid increase in population size in the 1980s and later its collapse by one and two years, respectively. Following the population collapse, spawning contracted away from historical regions towards southeastern areas of the Sound, and the proportion of occupied spawning areas declined from 65% to <9%. Spatial differences in spawn timing variation were also apparent, as the median spawn date shifted earlier by 26 days in eastern and 15 days in western areas of Prince William Sound between 1980 and 2006, and then shifted later by 25 (eastern) and 19 (western) days over a 7-year period. Effects of contracted spawning areas and timing shifts on first-year survival and recruitment are uncertain and require future investigation.