Local Watershed Properties Cannot Explain Divergent Dynamics of Pacific Herring in an Urbanizing Estuary Estuaries and Coasts

Pacific herring (Clupea pallasii) is a foundational species in Puget Sound (Washington State, U.S.A.) and is subject to many anthropogenic threats. We assessed the overall status of the Puget Sound Pacific herring sub-stock complex and asked whether watersheds with less urban or agricultural land cover, less impervious surface, and lower human density were associated with better stock status. To this end, we developed multiple metrics of sub-stock population status; characterized watershed properties with respect to land use/land cover, percent impervious surfaces, and human density; and used statistical model selection to evaluate the weight of evidence in support of our hypotheses. Overall, the status of sub-stocks was poor; metrics for most sub-stocks indicate a decline from 1996–2021. However, the status metrics of sub-stocks were not related to recent (2016) watershed characteristics or the rate of change in watershed characteristics from the mid-1990s to 2016. While the cumulative effects of local human land use throughout Puget Sound may be contributing to the deterioration of spawning biomass, these results also suggest that other drivers that operate at larger scales (e.g., predation, disease, climate) are likely important.

太平洋鲱（Pacific herring，学名Clupea pallasii）是美国华盛顿州普吉特海湾（Puget Sound）的关键建群物种，面临诸多人为活动带来的生存威胁。本研究评估了普吉特海湾太平洋鲱亚种群复合体的整体生存现状，并探讨了城市与农业用地占比更低、不透水面（impervious surface）占比更少、人类活动密度更低的流域，是否与更优的鲱鱼种群生存状态存在关联。为此，我们构建了多套亚种群生存状态评估指标；针对土地利用/土地覆被、不透水面占比及人类活动密度表征了流域属性特征；并通过统计模型选择（statistical model selection）方法，量化支持研究假说的证据权重。整体而言，多数亚种群的生存现状堪忧；1996年至2021年间，大部分亚种群的评估指标均呈现下降趋势。不过，亚种群的生存状态指标，与2016年的流域特征，以及1990年代中期至2016年的流域特征变化速率均无显著关联。尽管普吉特海湾全域的本地人类土地利用活动的累积效应，可能导致产卵生物量（spawning biomass）的下降，但本研究结果同时表明，其他更大尺度上的驱动因素（如捕食作用、疾病、气候变化）或同样发挥着关键作用。