Abstract In Lake Michigan, the unintended introduction of invasive species (e.g., zebra mussel, Dreissena polymorpha; quagga mussel, D. rostriformis bugensis; round goby, Neogobius melanostomus) and reduced nutrient loading has altered nutrient dynamics, system productivity, and community composition over the past two decades. These factors, together with sustained predation pressure, have contributed to declines of several forage fish species, including alewife (Alosa pseudoharengus), which has dominated diets of the five primary salmonine species of Lake Michigan for the last 50 years. Salmonines that have inflexible, less complex diets may struggle if alewife declines continue. We analyzed stomach contents of salmonines collected throughout the main basin of Lake Michigan in 2015 and 2016 to investigate diet composition, diet diversity, and individual variation of alewife lengths consumed. Chinook salmon (Oncorhynchus tshawytscha) almost exclusively consumed alewife and had lower diet diversities compared to the other four species, which consumed relatively high frequencies of round goby (brown trout, Salmo trutta; lake trout, Salvelinus namaycush), aquatic invertebrates (coho salmon, Oncorhynchus kisutch) and terrestrial invertebrates (rainbow trout, Oncorhynchus mykiss) along with alewife. Although clear spatio-temporal feeding patterns existed, much of the variation in diet composition and diet diversity was expressed at the individual level. Salmonine populations consumed the entire size range of alewife that were available, whereas individual stomachs tended to contain a narrow range of alewife sizes. Due to their reliance on alewife, it is likely that Chinook salmon will be more negatively impacted than other salmonine species if alewife abundance continues to decline in Lake Michigan.

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密歇根湖鲑鱼的饮食复杂性：2015-2016

摘要 在密歇根湖，入侵物种（如斑马贻贝、Dreissena polymorpha；斑驴贻贝、D. rostriformis bugensis；圆虾虎鱼、Neogobius melanostomus）的意外引入和营养负荷的减少改变了营养动态、系统生产力和群落组成。过去的两个十年。这些因素加上持续的捕食压力，导致了几种饲料鱼的数量减少，其中包括在过去 50 年里一直主导着密歇根湖五种主要鲑鱼种类的饮食的 alewife (Alosa pseudoharengus)。如果 alewife 继续下降，具有不灵活、不太复杂的饮食的鲑鱼可能会挣扎。我们分析了 2015 年和 2016 年在密歇根湖主要流域收集的鲑鱼的胃内容物，以调查饮食成分、饮食多样性、和消耗的 alewife 长度的个体差异。奇努克鲑鱼 (Oncorhynchus tshawytscha) 几乎只吃 alewife 并且饮食多样性低于其他四种，后者消耗相对较高频率的圆形虾虎鱼（褐鳟、Salmo trutta；湖鳟、Salvelinus namaycush）、水生无脊椎动物（银鲑鱼、 Oncorhynchus kisutch）和陆生无脊椎动物（虹鳟鱼，Oncorhynchus mykiss）以及 alewife。尽管存在明确的时空喂养模式，但饮食组成和饮食多样性的大部分变化表现在个体水平。Salmonine 种群消耗了可用的整个大小范围的 alewife，而单个胃往往包含范围狭窄的 alewife 大小。由于他们对alewife的依赖，