An ocean habitat trap? Impacts of global oxygen-minimum zone expansions on threatened apex predator ecology

由于气候驱动的溶解氧(DO)的减少，延伸到超过1000万千米的海洋(约占海洋体积的8%)的永久性最低含氧区(OMZ)在地理和垂直方向上都在扩大。对海洋动物分布和丰度的潜在影响可能对海洋中上层捕食者等高需氧量的顶端捕食者特别重要，因为它们通过OMZ浅滩活动减少了栖息地的数量，并将其进一步集中在更容易受到渔业影响的表层水域。但是，对被开发的海洋鱼类对OMZ扩展的实际反应的预测并不是建立在机械理解的基础上，主要是因为还没有确定在公开海洋中大型捕食性鱼类在正常行为期间的氧耐量的直接测量。这项拟议的研究将通过应用我们在动物运动研究方面的现有专业知识，并通过部署新的遥测技术来测量自由生活的海洋鲨鱼在OMZ上方/内部移动时实际遇到的氧气环境，从而改变我们对OMZ对海洋生态影响的理解。这将使关于海洋鲨鱼如何对OMZ做出生理和行为反应、海洋鲨鱼栖息地如何随着预测的OMZ扩大而变化以及这是否会增加鲨鱼对渔具的脆弱性等重大未知问题得到解决。该项目将通过对两个列入《红色名单》的物种--暖体(吸热性)短鳍金枪鱼和温性蓝鲨Prionace gluca通过深入研究鲨鱼就地反应的关键过程，我们的新建模方法将确定未来变暖和OMZ浅滩对鱼类生态位的影响，并确定这些转移分布和改变渔业捕捞风险的方式。该项目代表了一种将生理学与生态学和海洋学联系起来的跨学科方法，在了解全球生物对气候变暖和海洋除氧的反应与可持续渔业和物种养护直接相关方面取得了广泛的成果。

Permanent oxygen minimum zones (OMZs) that extend to over 10 million km3 of ocean (ca. 8% of ocean volume) are expanding geographically and vertically due to climate-driven reductions in dissolved oxygen (DO). Potential impacts on marine animal distributions and abundance may be particularly significant for high-oxygen-demand apex predators, such as oceanic pelagic sharks, by reducing habitat volumes through OMZ shoaling and concentrating them further in surface waters where they become more vulnerable to fisheries. But predictions of how exploited oceanic fish actually respond to OMZ expansions are not based on mechanistic understandings, principally because direct measurements of oxygen tolerances during normal behaviour have not been determined for large predatory fish in the open ocean. The proposed research will bring about a step change in our understanding of OMZ impacts on oceanic ecology by applying our existing expertise in animal movement studies and by deploying new telemetry technologies for measuring oxygen environments actually encountered by free-living oceanic sharks moving above/within OMZs. This will enable major unknowns to be addressed concerning how oceanic sharks respond physiologically and behaviourally to OMZs, how oceanic shark habitats change with predicted OMZ expansion, and whether this will increase shark vulnerability to fishing gear. The project will achieve its objectives through linked field and modelling studies on two Red-Listed species, the warm-bodied (endothermic) shortfin mako, Isurus oxyrinchus, and the ectothermic blue shark, Prionace glauca, that are the two pelagic shark species most frequently caught in high seas fisheries. By focusing in depth on key processes underlying shark responses to DO in situ, our new modelling approaches will establish effects of future warming and OMZ shoaling on fish niches and determine how these shift distributions and alter capture risk by fisheries. The project represents a discipline-spanning approach linking physiology to ecology and oceanography, with wide-ranging outcomes for understanding global biotic responses to warming and ocean deoxygenation with direct relevance to sustainable fisheries and species conservation.