Silver Carp Hypophthalmichthys molitrix and Bighead Carp H. nobilis, collectively known as bigheaded carps (BHC), are invasive fishes in the Mississippi River and surrounding basins. Increasing evidence suggests harmful impacts of BHC on native fisheries (e.g., competition). Monitoring the abundance of BHC is difficult with traditional fisheries gears, and few studies have evaluated early life stage sampling. Identifying the spawning locations of BHC through early life stage sampling has the ability to enhance management efforts by applying focus to areas that have potential to serve as population sources. We evaluated the performance of three gears in sampling larval BHC and native taxa within large-river tributaries in terms of abundance, community assemblage, and size structure. We sampled ichthyoplankton in tributaries with active (push net) and passive (drift net, light trap) gears from March through September 2016. Relative abundance of BHC was greatest in push nets followed by drift nets and was lowest in light traps. Native cyprinids and catostomids as well as BHC comprised a large portion of the total catch. Environmental and habitat characteristics (stream velocity, dissolved oxygen, and temperature) related to BHC reproduction influenced each gear’s ability to capture larval BHC, although relationships in final models were not significant. Taxonomic size selectivity existed among gears; in particular, larger BHC were collected in push nets relative to the other gears. Push nets were the most effective in sampling BHC, and remaining gears exhibited unique strengths. Although less effective than active push nets, drift nets proved useful for monitoring BHC in tributaries and may be advantageous in shallow systems with adequate flow. Light traps were ineffective at capturing BHC larvae in tributaries but may offer utility in lentic habitats or for native cyprinids. Our comparison serves as a guide for monitoring larval BHC in their invaded range and for detection in new areas, such as tributaries of the Great Lakes.

中文翻译：

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主动和被动幼体采样装置在大河流支流入侵鳙鱼繁殖监测中的比较

鲢鱼Hypophthalmichthys molitrix和鳙鱼H. nobilis统称为鳙鱼（BHC），是密西西比河及周边盆地的入侵鱼类。越来越多的证据表明六六六对本地渔业产生有害影响（例如，竞争）。使用传统的渔具很难监测 BHC 的丰度，而且很少有研究评估早期生命阶段的取样。通过早期生命阶段抽样确定 BHC 的产卵地点，能够通过将重点放在有可能成为种群来源的地区来加强管理工作。我们根据丰度、群落组合和大小结构评估了三个齿轮在大河流支流中采样幼虫 BHC 和本地类群的性能。我们用主动（推网）和被动（漂网，光阱）装置从 2016 年 3 月到 2016 年 9 月。BHC 的相对丰度在推网中最高，其次是流网，在光阱中最低。本地鲤鱼和鲶鱼以及六六六构成了总捕获量的很大一部分。与 BHC 繁殖相关的环境和栖息地特征（流速、溶解氧和温度）影响了每个装置捕获幼虫 BHC 的能力，尽管最终模型中的关系并不显着。齿轮之间存在分类尺寸选择性；特别是，相对于其他渔具，较大的六六六被收集在推网中。推网在对 BHC 进行采样时最有效，其余的齿轮表现出独特的优势。虽然不如主动推网有效，事实证明，流网对于监测支流中的 BHC 很有用，并且在流量充足的浅层系统中可能是有利的。光诱捕器在捕获支流中的 BHC 幼虫方面无效，但可能在静水生境或本地鲤鱼中提供实用性。我们的比较可作为在其入侵范围内监测幼虫 BHC 以及在新区域（例如五大湖的支流）进行检测的指南。