Abstract Adequate densities of zooplankton prey are critical for growth and survival of larvae of many fish species. Little information exists on the density of zooplankton in Great Lakes inshore areas during early spring, when larvae of important fishes rely on zooplankton. Reduced age-0 walleye recruitment and the absence of data on zooplankton availability for larval walleyes in northern Green Bay, Lake Michigan, led us to assess zooplankton densities during this critical spring period. We conducted biweekly vertical plankton tows in 2014–2016 near reefs and river plumes used by spawning walleyes for periods when larval walleyes were expected to be relying on zooplankton prey. Densities of zooplankton were well below literature values identified for good growth and survival of larval walleyes, averaging 1.5 individuals L−1 for all taxa and 0.12 individuals L−1 for large-bodied taxa across all sites and sampling dates. Various factors could contribute to the low density of zooplankton observed. We found low but significantly higher densities of cyclopoid copepods, nauplii, Bosmina, and total zooplankton at river mouth sites compared to open water sites. These results suggest that food availability for larval walleye in our study area was severely limiting which is consistent with the paucity of strong year classes observed since 2000. We suspect northern Green Bay has limited potential for producing strong year classes of walleyes under such conditions. Fishery managers working in unproductive waters should consider assessing the zooplankton community during critical periods to identify potential bottlenecks to reproductive success and larval fish survival.

中文翻译：

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甲壳类浮游动物可用于密歇根湖海湾的幼虫角膜白斑

摘要 足够的浮游动物猎物密度对许多鱼类幼虫的生长和存活至关重要。在早春，重要鱼类的幼虫依赖浮游动物，关于五大湖沿岸地区浮游动物密度的信息很少。减少 0 岁的角膜白斑招募以及缺乏密歇根湖格林湾北部的浮游动物幼虫可用浮游动物的数据，导致我们在这个关键的春季期间评估了浮游动物的密度。我们在 2014 年至 2016 年间每两周进行一次垂直浮游生物拖曳，在珊瑚礁和河羽附近产卵角膜白斑鱼的时期预计幼虫大眼目鱼依赖浮游动物猎物。浮游动物的密度远低于确定幼虫角膜白斑良好生长和存活的文献值，所有分类群平均有 1.5 个个体 L-1 和 0。12 个个体 L-1，用于所有地点和采样日期的大型分类群。各种因素可能导致所观察到的浮游动物密度低。我们发现，与开阔水域相比，河口地点的旋足类桡足类、无节幼体、波斯米纳和总浮游动物的密度较低但显着更高。这些结果表明，我们研究区的角膜白斑幼虫的食物供应受到严重限制，这与自 2000 年以来观察到的强年级的缺乏是一致的。我们怀疑在这种条件下，格林湾北部生产强年级的角膜白斑的潜力有限。在非生产性水域工作的渔业管理者应考虑在关键时期评估浮游动物群落，以确定繁殖成功和幼鱼存活的潜在瓶颈。