Earth to Oceans Research Group, Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada.
Central Coast Indigenous Resource Alliance, Campbell River, British Columbia, Canada.
Glob Chang Biol. 2022 Jan;28(1):72-85. doi: 10.1111/gcb.15895. Epub 2021 Oct 20.
Marine and freshwater ecosystems are increasingly at risk of large and cascading changes from multiple human activities (termed "regime shifts"), which can impact population productivity, resilience, and ecosystem structure. Pacific salmon exhibit persistent and large fluctuations in their population dynamics driven by combinations of intrinsic (e.g., density dependence) and extrinsic factors (e.g., ecosystem changes, species interactions). In recent years, many Pacific salmon have declined due to regime shifts but clear understanding of the processes driving these changes remains elusive. Here, we unpacked the role of density dependence, ecosystem trends, and stochasticity on productivity regimes for a community of five anadromous Pacific salmonids (Steelhead, Coho Salmon, Pink Salmon, Dolly Varden, and Coastal Cutthroat Trout) across a rich 40-year time-series. We used a Bayesian multivariate state-space model to examine whether productivity shifts had similarly occurred across the community and explored marine or freshwater changes associated with those shifts. Overall, we identified three productivity regimes: an early regime (1976-1990), a compensatory regime (1991-2009), and a declining regime (since 2010) where large declines were observed for Steelhead, Dolly Varden, and Cutthroat Trout, intermediate declines in Coho and no change in Pink Salmon. These regime changes were associated with multiple cumulative effects across the salmon life cycle. For example, increased seal densities and ocean competition were associated with lower adult marine survival in Steelhead. Watershed logging also intensified over the past 40 years and was associated with (all else equal) ≥97% declines in freshwater productivity for Steelhead, Cutthroat, and Coho. For Steelhead, marine and freshwater dynamics played approximately equal roles in explaining trends in total productivity. Collectively, these changing environments limited juvenile production and lowered future adult returns. These results reveal how changes in freshwater and marine environments can jointly shape population dynamics among ecological communities, like Pacific salmon, with cascading consequences to their resilience.
海洋和淡水生态系统越来越受到多种人类活动（称为“生态系统状态转变”）的威胁，这些活动可能会影响种群生产力、恢复力和生态系统结构。太平洋鲑鱼的种群动态呈现出持久而巨大的波动，这是由内在因素（如密度依赖）和外在因素（如生态系统变化、物种相互作用）共同作用的结果。近年来，由于生态系统状态转变，许多太平洋鲑鱼的数量下降，但对于驱动这些变化的过程仍缺乏清晰的认识。在这里，我们剖析了密度依赖、生态系统趋势和随机性对 5 种洄游性太平洋鲑鱼（虹鳟、银鲑、粉鲑、多利鱒和沿海斑鳜）群落生产力模式的作用，该群落跨越了一个丰富的 40 年时间序列。我们使用贝叶斯多元状态空间模型来检验生产力是否在整个群落中发生了转变，并探讨了与这些转变相关的海洋或淡水变化。总体而言，我们确定了三种生产力模式：早期模式（1976-1990 年）、补偿模式（1991-2009 年）和下降模式（自 2010 年以来），在下降模式中，虹鳟、多利鱒和斑鳜的数量大幅下降，银鲑和粉鲑的数量中等下降。这些生态系统状态的转变与鲑鱼生命周期中的多种累积效应有关。例如，海豹密度的增加和海洋竞争与虹鳟成鱼的海洋存活率降低有关。过去 40 年来，流域采伐的强度也在加剧，与虹鳟、斑鳜和银鲑的淡水生产力下降≥97%有关。对于虹鳟来说，海洋和淡水动态在解释其总生产力趋势方面发挥了同等重要的作用。总的来说，这些不断变化的环境限制了幼鱼的生产，降低了未来成鱼的数量。这些结果揭示了淡水和海洋环境的变化如何共同塑造太平洋鲑鱼等生态群落的种群动态，对其恢复力产生级联影响。
