Peterson Sarah H, Ackerman Joshua T, Costa Daniel P
Department of Ecology and Evolutionary Biology, University of California, 100 Shaffer Road, Santa Cruz, CA 95060, USA
US Geological Survey, Western Ecological Research Center, Dixon Field Station, 800 Business Park Drive, Suite D, Dixon, CA 95620, USA.
Proc Biol Sci. 2015 Jul 7;282(1810). doi: 10.1098/rspb.2015.0710.
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 δ(13)C 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.
海洋汞污染在全球范围内普遍存在，海洋中层带（200 - 1000米）的甲基汞浓度比表层水增长得更快。然而，海洋中层带捕食者体内汞的生物积累情况却鲜有研究。北方海象（Mirounga angustirostris）每年两次跋涉数千公里，在东北太平洋的沿海和公海区域觅食。我们结合了77只成年雌性海象的卫星遥测、潜水行为和稳定同位素（碳和氮）数据，结果表明，个体在觅食地点、潜水深度和δ(13)C值方面的差异与血液和肌肉中的汞浓度相关。我们确定了三种觅食策略集群，这些集群导致汞浓度有显著差异：（i）潜水更深且在近海觅食的海象汞浓度最高，（ii）潜水较浅且在近海觅食的海象汞浓度处于中等水平，（iii）在沿海和更靠北区域觅食的海象汞浓度最低。此外，在为期七个月的觅食之旅结束时（n = 31），汞浓度低于为期两个月的繁殖后之旅结束时（n = 46）。我们的研究结果表明，觅食行为会影响汞暴露，在东北太平洋觅食的海洋中层带捕食者可能面临汞生物积累的高风险。
