Delta smelt struggle to persist in a dramatically altered estuarine environment. Complex and incompletely understood relationships between food availability, environmental stressors, other components of the species’ habitat, and the abundance of delta smelt impede the effective management and recovery of the species. The empirical modeling presented in this study quantitatively describes spatial-temporal biomass values of calanoid copepods, a key prey item for delta smelt, in relation to multiple potential controlling factors. The results underscore the role that river flows through the estuary have in determining prey availability, and demonstrate contributions of water temperature, salinity, and macronutrients in determining copepod biomass. The analysis also shows the importance of non-native, invasive bivalves in determining copepod biomass. Importantly, the analysis describes spatial-temporal shifts in the relative importance of modeled covariates across sampling locations in the Delta. Model results indicate that increasing flows in the fall of wetter years adversely affected copepod biomass, while increases in flows in the spring of drier years provided regional increases in biomass. The results of this analysis can inform resource management decisions and contribute to a comprehensive model that can meaningfully guide efforts to recover the imperiled delta smelt.

中文翻译：

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旧金山河口上游类角足类生物量和分布的控制因素以及对管理危险三角洲冶炼（Hypomesus transpacificus）的影响

三角洲冶炼厂在急剧变化的河口环境中挣扎求生。食物供应、环境压力因素、物种栖息地的其他组成部分以及丰富的三角洲胡瓜之间的复杂和不完全了解的关系阻碍了该物种的有效管理和恢复。本研究中提出的经验模型定量描述了与多个潜在控制因素相关的角足类动物（三角洲冶炼的关键猎物）的时空生物量值。结果强调了河流流经河口在确定猎物可用性方面的作用，并证明了水温、盐度和常量营养素对确定桡足类生物量的贡献。该分析还显示了非本地入侵双壳类动物在确定桡足类生物量方面的重要性。重要的是，该分析描述了 Delta 中各个采样位置的建模协变量的相对重要性的时空变化。模型结果表明，在较湿润年份秋季增加流量对桡足类生物量产生不利影响，而在较干旱年份春季流量增加提供区域生物量增加。该分析的结果可以为资源管理决策提供信息，并有助于建立一个综合模型，该模型可以有意义地指导恢复受威胁的三角洲冶炼的努力。而在较干旱年份的春季流量的增加提供了区域生物量的增加。该分析的结果可以为资源管理决策提供信息，并有助于建立一个综合模型，该模型可以有意义地指导恢复受威胁的三角洲冶炼的努力。而在较干旱年份的春季流量的增加提供了区域生物量的增加。该分析的结果可以为资源管理决策提供信息，并有助于建立一个综合模型，该模型可以有意义地指导恢复受威胁的三角洲冶炼的努力。