Data from: Marine foraging ecology influences mercury bioaccumulation in deep-diving northern elephant seals

Mercury contamination of oceans is prevalent worldwide and methylmercury concentrations in the mesopelagic zone (200–1000 m) are increasing more rapidly than in surface waters. Yet mercury bioaccumulation in mesopelagic predators has been understudied. Northern elephant seals (Mirounga angustirostris) biannually travel thousands of kilometres to forage within coastal and open-ocean regions of the northeast Pacific Ocean. We coupled satellite telemetry, diving behaviour and stable isotopes (carbon and nitrogen) from 77 adult females, and showed that variability among individuals in foraging location, diving depth and δ13C values were correlated with mercury concentrations in blood and muscle. We identified three clusters of foraging strategies, and these resulted in substantially different mercury concentrations: (i) deeper-diving and offshore-foraging seals had the greatest mercury concentrations, (ii) shallower-diving and offshore-foraging seals had intermediate levels, and (iii) coastal and more northerly foraging seals had the lowest mercury concentrations. Additionally, mercury concentrations were lower at the end of the seven-month-long foraging trip (n = 31) than after the two-month- long post-breeding trip (n = 46). Our results indicate that foraging behaviour influences mercury exposure and mesopelagic predators foraging in the northeast Pacific Ocean may be at high risk for mercury bioaccumulation.全球海洋普遍存在汞污染，中层带（mesopelagic zone，200–1000米）的甲基汞（methylmercury）浓度增长速率较表层海水更快。然而学界对中层带捕食者体内的汞生物累积（mercury bioaccumulation）现象研究不足。北象海豹（Mirounga angustirostris）每半年会跋涉数千公里，前往东北太平洋的近岸与远洋海域觅食。本研究整合了77头成年雌性北象海豹的卫星遥测（satellite telemetry）数据、潜水行为数据以及稳定同位素（stable isotopes，碳、氮）数据，结果显示：个体间觅食位置、潜水深度以及δ13C值的差异，与其血液和肌肉中的汞浓度显著相关。我们识别出三类不同的觅食策略集群，三者对应的汞浓度差异显著：（i）深潜远洋觅食的海豹体内汞浓度最高；（ii）浅潜远洋觅食的海豹体内汞浓度处于中等水平；（iii）近岸且更偏北觅食的海豹体内汞浓度最低。此外，在为期7个月的觅食旅程结束时（n=31），海豹体内的汞浓度要低于为期2个月的繁殖后觅食旅程结束后（n=46）的汞浓度。本研究结果表明，觅食行为会影响汞暴露（mercury exposure）水平，东北太平洋中层带捕食者可能面临较高的汞生物累积风险。