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

David W Mcgowan,Mark D Scheuerell,Trevor A Branch,Stormy Haught

doi:10.1139/cjfas-2021-0047

Abstract

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.

Highlights

The location and time of spawning plays a critical role in the survival of pelagic fish during early life stages that subsequently affects recruitment
In the 1970s, survey coverage was primarily focused in the Northeast Shore region (11.6 days sampled per year versus < 4 d y-1 in other regions, Table 1)
Prince William Sound in the early 1980s (Table S1), with flights occurring over all regions within the Sound on more than 50% of the days sampled per year (Table 1), peaking at 30 d y-1 at the peak of population size (Fig. 1)

Summary

Introduction

The location and time of spawning plays a critical role in the survival of pelagic fish during early life stages that subsequently affects recruitment. Temporal shifts in spawning can affect the duration of egg and larval stages (Houde 2016), predation risk, and the availability of prey to larvae during the critical early feeding period (Cushing 1990). Individual herring spawn once per season, staggered spawning across the entire population in space and time has the effect of hedging against uncertainty in the timing and location of optimal conditions for egg and larval survival (Lambert 1990). Spatial and temporal diversity in spawning among metapopulations buffers the larger population from abundance fluctuations (i.e., the portfolio effect, Schindler et al 2010) -- herring spawning that is broadly distributed in space and time increases population resilience to perturbations in their environment (Hay 1985; Lambert 1987; Siple and Francis 2016). Changes in the number or spatial diversity of spawning locations, and temporal shifts in the onset or duration of spawning may impact long-term productivity of herring populations (Ruzzante et al 2006; Dragesund et al.2008)

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Conclusion