Trophic structure and mercury transfer in the subarctic fish community of Great Slave Lake, Northwest Territories, Canada

In recent decades, mercury concentrations have increased in fish of Great Slave Lake (GSL), a subarctic great lake in northern Canada with important recreational, subsistence, and commercial fisheries. This study characterized habitat use and trophic position of common fish species in GSL near the City of Yellowknife (Northwest Territories, Canada), measured mercury concentrations in water and in taxa from lower trophic levels of the food web, and examined trophic and biological influences on mercury concentrations within and among fish species. Northern pike (Exos lucius) and lake whitefish (Coregonus clupeformis) fed predominantly nearshore, cisco (Coregonus artedi) and longnose sucker (Catostomus catostomus) fed predominantly offshore, and burbot (Lota lota) fed roughly equally in both habitats. Habitat-specific feeding did not influence mercury bioaccumulation in fish, in contrast with published studies of smaller lakes. Water concentrations of total mercury and methylmercury were low and showed little spatial variation among sites or depths. Zooplankton (>200 µm) had similarly low methylmercury concentrations to littoral and profundal amphipods, suggesting little habitat-variation of mercury exposure near the base of the food web. Age, size, and trophic position were significant explanatory variables for muscle total mercury concentrations within populations of fish species. Among fish species, size and trophic position explained 80% of the variation in muscle total mercury concentrations. This study generated the most comprehensive dataset to date on mercury bioaccumulation in the food web of GSL, which will serve as a baseline for future studies of this great lake.

近几十年来，加拿大北部亚寒带大型湖泊大奴湖（Great Slave Lake, GSL）内鱼类的汞浓度呈上升趋势，该湖泊兼具重要的休闲、生计与商业渔业价值。本研究针对加拿大西北地区耶洛奈夫市附近大奴湖内常见鱼类的栖息地利用模式与营养位特征展开解析，测定了水体及食物网低营养级类群的汞浓度，并探究了鱼类物种内部及物种间汞浓度受营养与生物因素的影响情况。研究发现，白斑狗鱼（*Exos lucius*）与湖白鲑（*Coregonus clupeformis*）主要在近岸区域觅食，西斯科白鲑（*Coregonus artedi*）与长鼻吸口鱼（*Catostomus catostomus*）主要活动于远岸生境，而江鳕（*Lota lota*）在两种生境中的觅食比例大致相当。与已发表的小型湖泊研究结果不同，基于特定栖息地的觅食模式并未对鱼类体内的汞生物富集产生影响。水体总汞与甲基汞浓度处于较低水平，且在不同采样点位与水深间几乎无空间差异。粒径>200μm的浮游动物其甲基汞浓度与沿岸及深底端足类相近，表明食物网基部附近的汞暴露生境差异极小。对于各鱼类种群而言，年龄、体长及营养位是解释其肌肉组织总汞浓度的显著变量。跨物种层面，体长与营养位可解释肌肉总汞浓度80%的变异量。本研究构建了目前针对大奴湖食物网汞生物富集最为全面的数据集，将为该大型湖泊的后续相关研究提供基准参照。