Data from: Environmental context and contaminant biotransport by Pacific salmon interact to mediate the bioaccumulation of contaminants by stream-resident fish

1.The extent to which environmental context mediates the bioaccumulation of biotransported contaminants by stream-resident organisms is poorly understood. For example, it is unclear the extent to which contaminant type, instream characteristics, or resident fish identity interact to influence the uptake of contaminants deposited by Pacific salmon (Oncorhynchus spp.) during their spawning runs. 2.To address this uncertainty, we sampled four stream-resident fish species from 13 watersheds of the Laurentian Great Lakes in locations with and without salmon runs across a gradient of instream and watershed characteristics. We determined the polychlorinated biphenyl (PCB) and mercury (Hg) concentration along with the stable isotope ratios for salmon and stream-resident fish. 3.We found that stream-resident fish PCB concentrations were higher in reaches with salmon and were positively related to δ15N. In contrast, resident fish Hg concentrations were similar or lower in reaches with salmon compared to reaches lacking salmon and either exhibited a negative or no relationship with δ15N. 4.Based upon AICc, resident fish exhibited species-specific PCB concentrations that were positively related to salmon PCB flux. Hg burdens exhibited an interaction between fish length and salmon Hg flux – as salmon Hg inputs increased, Hg levels decreased with increasing resident fish length. Because salmon eggs are enriched in PCBs but depleted in Hg, contaminant loads of resident fish appear to be driven by consumption of salmon eggs. We found no support for models that included the mediating influence of instream or watershed factors. 5.Synthesis and applications. Our results highlight that contaminants bioaccumulate differently depending on contaminant type, species identity, and the trophic pathway to contamination. Consequently, consideration of the recipient food web and route of exposure is critical to understanding the fate of biotransported contaminants in ecosystems. The transfer of contaminants by migratory organisms represents an understudied stressor in ecology. Effective management of biotransported contaminants will require the delineation of hotspots of biotransport and implementation of best management practices to reduce inputs of salmon-derived pollutants.1. 目前学界对环境背景介导溪流栖息生物（stream-resident organisms）对生物转运污染物（biotransported contaminants）的生物富集（bioaccumulation）程度仍知之甚少。例如，尚不清楚污染物类型、溪流生境特征（instream characteristics）与栖息鱼类种类（resident fish identity）三者间的交互作用，会在多大程度上影响太平洋鲑（Oncorhynchus spp.）洄游产卵时所沉降污染物的摄取过程。 2. 为厘清这一认知空白，我们于劳伦琴五大湖（Laurentian Great Lakes）的13个流域内，选取存在鲑鱼洄游与不存在鲑鱼洄游的点位，覆盖不同梯度的溪流生境与流域特征，共采集了4种溪流栖息鱼类样本。同时测定了鲑鱼与溪流栖息鱼类体内的多氯联苯（polychlorinated biphenyl, PCB）、汞（mercury, Hg）浓度，以及稳定同位素比值（stable isotope ratios）。 3. 研究结果显示，存在鲑鱼洄游的河段内，溪流栖息鱼类的多氯联苯浓度更高，且与δ15N呈正相关关系。与之相反，相较于无鲑鱼洄游的河段，存在鲑鱼洄游的河段中栖息鱼类的汞浓度相近甚至更低，且其与δ15N要么呈负相关，要么无显著关联。 4. 基于AICc模型选择标准，栖息鱼类的多氯联苯浓度具有物种特异性，且与鲑鱼的多氯联苯通量呈正相关。而鱼类体内汞负荷则与鱼体长度及鲑鱼汞通量存在交互效应：随着鲑鱼汞输入量增加，栖息鱼类体内汞水平随其体长增长而降低。由于鲑鱼卵（salmon eggs）富集多氯联苯但汞含量相对匮乏，栖息鱼类的污染物负荷似乎由摄食鲑鱼卵所驱动。本研究未发现支持溪流生境或流域因素起到介导作用的模型证据。 5. 总结与应用。本研究结果表明，污染物的生物富集模式因污染物类型、物种种类以及污染营养通路的不同而存在差异。因此，要理解生态系统中生物转运污染物的归趋，需重点考量受纳食物网与暴露途径。由洄游生物（migratory organisms）介导的污染物迁移，在生态学领域仍是一个尚未得到充分研究的胁迫因子（stressor）。对生物转运污染物进行有效管理，需要明确生物转运热点区域，并实施最佳管理措施（best management practices）以减少鲑鱼来源污染物的输入。