Steingass Sheanna, Horning Markus
Department of Fisheries and Wildlife, Marine Mammal Institute, Oregon State University, Hatfield Marine Science Center, 2030 SE Marine Science Drive, Newport, OR, USA.
Department of Fisheries and Wildlife, Marine Mammal Institute, Oregon State University, Hatfield Marine Science Center, 2030 SE Marine Science Drive, Newport, OR, USA; Alaska SeaLife Center, 301 Railway Ave, Seward, AK 99644, USA.
J Theor Biol. 2017 Mar 7;416:190-198. doi: 10.1016/j.jtbi.2017.01.006. Epub 2017 Jan 9.
Wind-driven coastal hypoxia represents an environmental stressor that has the potential to drive redistribution of gilled marine organisms, and thereby indirectly affect the foraging characteristics of air-breathing upper trophic-level predators. We used a conceptual individual-based model to simulate effects of coastal hypoxia on the spatial foraging behavior and efficiency of a marine mammal, the Pacific harbor seal (Phoca vitulina richardii) on the Oregon coast. Habitat compression of fish was simulated at varying intensities of hypoxia. Modeled hypoxia affected up to 80% of the water column and half of prey species' horizontal habitat. Pacific sand lance (Ammodytes hexapterus), Pacific herring (Clupea pallasii), and English sole (Parophrys vetulus) were selected as representative harbor seal prey species. Model outputs most affected by coastal hypoxia were seal travel distance to foraging sites, time spent at depth during foraging dives, and daily energy balance. For larger seals, English sole was the most optimal prey during normoxia, however during moderate to severe hypoxia Pacific sand lance was the most beneficial prey. For smaller seals, Pacific herring was the most efficient prey species during normoxia, but sand lance became more efficient as hypoxia increased. Sand lance represented the highest increase in foraging efficiency during severe hypoxic events for all seals. Results suggest that during increasing hypoxia, smaller adult harbor seals could benefit by shifting from foraging on larger neritic schooling fishes to foraging closer inshore on less energetically-dense forage fish. Larger adult seals may benefit by shifting from foraging on groundfish to smaller, schooling neritic fishes as hypoxia increases. The model suggests a mechanism by which hypoxia may result in increased foraging efficiency of Pacific harbor seals, and therefore increased rates of predation on coastal fishes on the continental shelf during hypoxic events.
风生沿岸低氧是一种环境压力源，有可能促使有鳃海洋生物重新分布，从而间接影响空气呼吸的高营养级捕食者的觅食特性。我们使用了一个基于个体的概念模型，来模拟沿岸低氧对俄勒冈海岸的一种海洋哺乳动物——太平洋港海豹（Phoca vitulina richardii）的空间觅食行为和效率的影响。在不同强度的低氧条件下模拟了鱼类栖息地的压缩情况。模拟的低氧影响了高达80%的水柱和一半的猎物物种水平栖息地。太平洋沙鳗（Ammodytes hexapterus）、太平洋鲱鱼（Clupea pallasii）和星斑川鲽（Parophrys vetulus）被选为港海豹的代表性猎物物种。受沿岸低氧影响最大的模型输出是海豹前往觅食地点的行进距离、觅食潜水时在深处停留的时间以及每日能量平衡。对于较大的海豹，在正常氧含量条件下，星斑川鲽是最理想的猎物，然而在中度至重度低氧期间，太平洋沙鳗是最有益的猎物。对于较小的海豹，在正常氧含量条件下，太平洋鲱鱼是最有效的猎物物种，但随着低氧程度增加，沙鳗变得更有效。在严重低氧事件期间，沙鳗对所有海豹来说觅食效率提高幅度最大。结果表明，在低氧加剧期间，较小的成年港海豹可能会受益于从在较大的近岸集群鱼类觅食转向在能量密度较低的沿岸小型饵料鱼近岸觅食。随着低氧增加，较大的成年海豹可能会受益于从底栖鱼类觅食转向较小的近岸集群鱼类。该模型提出了一种机制，通过这种机制低氧可能导致太平洋港海豹觅食效率提高，从而在低氧事件期间增加对大陆架沿岸鱼类的捕食率。
