Fishery along the west coast of India largely depends on pelagic fish such as oil sardines, which are dominant during the south‐west monsoon. However, the response of sardine population to the warming caused by the climatic events such as El Niño/Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) is poorly studied. Here, we hypothesize that the ENSO‐related changes in biogeochemistry can adversely affect the oil sardines. We have used biogeochemical data collected along the Kerala coast during September 2015 (ENSO year) and September 2017 (a normal year) supported by catch per unit effort (CPUE) and fishery landing data to show the ENSO‐related bio‐physical dynamics and its impact on the oil sardine population along the south‐west coast of India. During the 2015 ENSO year, upwelling velocity decreased minimizing cooling of surface waters and resulted with an increase in sea surface temperature (SST) (~1.8°C). Consequent decrease in nutrient levels favoured nano‐phytoplankton and pico‐phytoplankton. On the other hand, during September 2017 when the ENSO effect was nullified, the decreased SST and availability of nutrients in the euphotic zone resulted in the dominance of micro‐phytoplankton. The hydrographic conditions (reduction in upwelling intensity), and reduction in micro‐phytoplankton abundance and zooplankton density in turn perhaps affected the fishery potential of the region. Oil sardines population (along the west coast) collapsed from 1.55 lakh tones (2014) to 0.46 lakh tones during 2015–2016 ENSO event, while in 2017 the conditions become favorable and their population was back to normal (1.27 lakh tones). Our results are in close agreement with our hypothesis and suggest that ENSO events could reduce phytoplankton productivity and disrupt the food chain, which in turn can affect the oil sardine population along the west coast of India.

中文翻译：

---

2015–16年ENSO有助于减少印度西南部喀拉拉邦沿岸的沙丁鱼油

印度西海岸的渔业在很大程度上依赖上层鱼类，例如沙丁鱼，它们在西南季风中占主导地位。然而，沙丁鱼种群对诸如厄尔尼诺现象/南方涛动（ENSO）和印度洋偶极子（IOD）等气候事件引起的变暖的响应研究很少。在这里，我们假设ENSO相关的生物地球化学变化可能会对沙丁鱼油产生不利影响。我们使用了2015年9月（ENSO年）和2017年9月（正常年）沿喀拉拉海岸收集的生物地球化学数据，并结合每单位捕捞量（CPUE）和渔业着陆数据，显示了ENSO相关的生物物理动力学及其变化。对印度西南沿海沙丁鱼种群的影响。在2015 ENSO年，上升流速度降低，使地表水冷却降到最低，并导致海表温度（SST）（〜1.8°C）升高。因此，营养水平的下降有利于纳米浮游植物和微型浮游植物。另一方面，在ENSO效应消失的2017年9月，富营养区SST的降低和养分的可利用性导致了微浮游植物的优势。水文条件（上升流强度的降低）以及微浮游植物的丰度和浮游动物密度的降低可能反过来影响了该地区的渔业潜力。在2015年至2016年ENSO事件中，沙丁鱼种群（沿西海岸）从15.5亿吨（2014年）下降至0.46亿吨，而2017年情况变得有利，其种群恢复了正常（1。270万音）。我们的结果与我们的假设非常吻合，表明ENSO事件可能会降低浮游植物的生产力并破坏食物链，进而影响印度西海岸的沙丁鱼种群。